Merge release-20200518.0-45-g0bc022b7 (automated)

644 files changed, 5566 insertions, 321 deletions

diff --git a/pkg/abi/abi_linux_state_autogen.go b/pkg/abi/abi_linux_state_autogen.go
index 327ef0e5c..327ef0e5c 100755..100644
--- a/pkg/abi/abi_linux_state_autogen.go
+++ b/pkg/abi/abi_linux_state_autogen.go
diff --git a/pkg/abi/abi_state_autogen.go b/pkg/abi/abi_state_autogen.go
index d54002c3b..d54002c3b 100755..100644
--- a/pkg/abi/abi_state_autogen.go
+++ b/pkg/abi/abi_state_autogen.go
diff --git a/pkg/abi/linux/arch_amd64.go b/pkg/abi/linux/arch_amd64.go
index 0be31e755..0be31e755 100755..100644
--- a/pkg/abi/linux/arch_amd64.go
+++ b/pkg/abi/linux/arch_amd64.go
diff --git a/pkg/abi/linux/epoll_amd64.go b/pkg/abi/linux/epoll_amd64.go
index 7e74b1143..7e74b1143 100755..100644
--- a/pkg/abi/linux/epoll_amd64.go
+++ b/pkg/abi/linux/epoll_amd64.go
diff --git a/pkg/abi/linux/epoll_arm64.go b/pkg/abi/linux/epoll_arm64.go
index a35939cc9..a35939cc9 100755..100644
--- a/pkg/abi/linux/epoll_arm64.go
+++ b/pkg/abi/linux/epoll_arm64.go
diff --git a/pkg/abi/linux/file_amd64.go b/pkg/abi/linux/file_amd64.go
index 6b72364ea..6b72364ea 100755..100644
--- a/pkg/abi/linux/file_amd64.go
+++ b/pkg/abi/linux/file_amd64.go
diff --git a/pkg/abi/linux/file_arm64.go b/pkg/abi/linux/file_arm64.go
index 6492c9038..6492c9038 100755..100644
--- a/pkg/abi/linux/file_arm64.go
+++ b/pkg/abi/linux/file_arm64.go
diff --git a/pkg/abi/linux/ioctl_tun.go b/pkg/abi/linux/ioctl_tun.go
index c59c9c136..c59c9c136 100755..100644
--- a/pkg/abi/linux/ioctl_tun.go
+++ b/pkg/abi/linux/ioctl_tun.go
diff --git a/pkg/abi/linux/linux_abi_autogen_unsafe.go b/pkg/abi/linux/linux_abi_autogen_unsafe.go
index 6d0ae0409..d351e2186 100755..100644
--- a/pkg/abi/linux/linux_abi_autogen_unsafe.go
+++ b/pkg/abi/linux/linux_abi_autogen_unsafe.go
@@ -129,7 +129,7 @@ func (s *Statx) Packed() bool {
 
 // MarshalUnsafe implements marshal.Marshallable.MarshalUnsafe.
 func (s *Statx) MarshalUnsafe(dst []byte) {
-    if s.Atime.Packed() && s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() {
+    if s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() && s.Atime.Packed() {
         safecopy.CopyIn(dst, unsafe.Pointer(s))
     } else {
         s.MarshalBytes(dst)
@@ -138,7 +138,7 @@ func (s *Statx) MarshalUnsafe(dst []byte) {
 
 // UnmarshalUnsafe implements marshal.Marshallable.UnmarshalUnsafe.
 func (s *Statx) UnmarshalUnsafe(src []byte) {
-    if s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() && s.Atime.Packed() {
+    if s.Ctime.Packed() && s.Mtime.Packed() && s.Atime.Packed() && s.Btime.Packed() {
         safecopy.CopyOut(unsafe.Pointer(s), src)
     } else {
         s.UnmarshalBytes(src)
@@ -148,7 +148,7 @@ func (s *Statx) UnmarshalUnsafe(src []byte) {
 // CopyOutN implements marshal.Marshallable.CopyOutN.
 //go:nosplit
 func (s *Statx) CopyOutN(task marshal.Task, addr usermem.Addr, limit int) (int, error) {
-    if !s.Mtime.Packed() && s.Atime.Packed() && s.Btime.Packed() && s.Ctime.Packed() {
+    if !s.Atime.Packed() && s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() {
         // Type Statx doesn't have a packed layout in memory, fall back to MarshalBytes.
         buf := task.CopyScratchBuffer(s.SizeBytes()) // escapes: okay.
         s.MarshalBytes(buf) // escapes: fallback.
@@ -178,7 +178,7 @@ func (s *Statx) CopyOut(task marshal.Task, addr usermem.Addr) (int, error) {
 // CopyIn implements marshal.Marshallable.CopyIn.
 //go:nosplit
 func (s *Statx) CopyIn(task marshal.Task, addr usermem.Addr) (int, error) {
-    if !s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() && s.Atime.Packed() {
+    if !s.Atime.Packed() && s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() {
         // Type Statx doesn't have a packed layout in memory, fall back to UnmarshalBytes.
         buf := task.CopyScratchBuffer(s.SizeBytes()) // escapes: okay.
         length, err := task.CopyInBytes(addr, buf) // escapes: okay.
@@ -204,7 +204,7 @@ func (s *Statx) CopyIn(task marshal.Task, addr usermem.Addr) (int, error) {
 
 // WriteTo implements io.WriterTo.WriteTo.
 func (s *Statx) WriteTo(w io.Writer) (int64, error) {
-    if !s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() && s.Atime.Packed() {
+    if !s.Atime.Packed() && s.Btime.Packed() && s.Ctime.Packed() && s.Mtime.Packed() {
         // Type Statx doesn't have a packed layout in memory, fall back to MarshalBytes.
         buf := make([]byte, s.SizeBytes())
         s.MarshalBytes(buf)
diff --git a/pkg/abi/linux/linux_amd64_abi_autogen_unsafe.go b/pkg/abi/linux/linux_amd64_abi_autogen_unsafe.go
index 1ab6ec3f5..ad674f6de 100755..100644
--- a/pkg/abi/linux/linux_amd64_abi_autogen_unsafe.go
+++ b/pkg/abi/linux/linux_amd64_abi_autogen_unsafe.go
@@ -293,7 +293,7 @@ func (s *Stat) Packed() bool {
 
 // MarshalUnsafe implements marshal.Marshallable.MarshalUnsafe.
 func (s *Stat) MarshalUnsafe(dst []byte) {
-    if s.CTime.Packed() && s.ATime.Packed() && s.MTime.Packed() {
+    if s.MTime.Packed() && s.CTime.Packed() && s.ATime.Packed() {
         safecopy.CopyIn(dst, unsafe.Pointer(s))
     } else {
         s.MarshalBytes(dst)
@@ -302,7 +302,7 @@ func (s *Stat) MarshalUnsafe(dst []byte) {
 
 // UnmarshalUnsafe implements marshal.Marshallable.UnmarshalUnsafe.
 func (s *Stat) UnmarshalUnsafe(src []byte) {
-    if s.MTime.Packed() && s.CTime.Packed() && s.ATime.Packed() {
+    if s.ATime.Packed() && s.MTime.Packed() && s.CTime.Packed() {
         safecopy.CopyOut(unsafe.Pointer(s), src)
     } else {
         s.UnmarshalBytes(src)
@@ -342,7 +342,7 @@ func (s *Stat) CopyOut(task marshal.Task, addr usermem.Addr) (int, error) {
 // CopyIn implements marshal.Marshallable.CopyIn.
 //go:nosplit
 func (s *Stat) CopyIn(task marshal.Task, addr usermem.Addr) (int, error) {
-    if !s.ATime.Packed() && s.MTime.Packed() && s.CTime.Packed() {
+    if !s.MTime.Packed() && s.CTime.Packed() && s.ATime.Packed() {
         // Type Stat doesn't have a packed layout in memory, fall back to UnmarshalBytes.
         buf := task.CopyScratchBuffer(s.SizeBytes()) // escapes: okay.
         length, err := task.CopyInBytes(addr, buf) // escapes: okay.
diff --git a/pkg/abi/linux/linux_amd64_state_autogen.go b/pkg/abi/linux/linux_amd64_state_autogen.go
index 58cabce4c..58cabce4c 100755..100644
--- a/pkg/abi/linux/linux_amd64_state_autogen.go
+++ b/pkg/abi/linux/linux_amd64_state_autogen.go
diff --git a/pkg/abi/linux/linux_arm64_abi_autogen_unsafe.go b/pkg/abi/linux/linux_arm64_abi_autogen_unsafe.go
index a5a5f78aa..69d75f6bc 100755..100644
--- a/pkg/abi/linux/linux_arm64_abi_autogen_unsafe.go
+++ b/pkg/abi/linux/linux_arm64_abi_autogen_unsafe.go
@@ -309,7 +309,7 @@ func (s *Stat) MarshalUnsafe(dst []byte) {
 
 // UnmarshalUnsafe implements marshal.Marshallable.UnmarshalUnsafe.
 func (s *Stat) UnmarshalUnsafe(src []byte) {
-    if s.CTime.Packed() && s.ATime.Packed() && s.MTime.Packed() {
+    if s.ATime.Packed() && s.MTime.Packed() && s.CTime.Packed() {
         safecopy.CopyOut(unsafe.Pointer(s), src)
     } else {
         s.UnmarshalBytes(src)
@@ -375,7 +375,7 @@ func (s *Stat) CopyIn(task marshal.Task, addr usermem.Addr) (int, error) {
 
 // WriteTo implements io.WriterTo.WriteTo.
 func (s *Stat) WriteTo(w io.Writer) (int64, error) {
-    if !s.CTime.Packed() && s.ATime.Packed() && s.MTime.Packed() {
+    if !s.ATime.Packed() && s.MTime.Packed() && s.CTime.Packed() {
         // Type Stat doesn't have a packed layout in memory, fall back to MarshalBytes.
         buf := make([]byte, s.SizeBytes())
         s.MarshalBytes(buf)
diff --git a/pkg/abi/linux/linux_arm64_state_autogen.go b/pkg/abi/linux/linux_arm64_state_autogen.go
index 301a5cb76..301a5cb76 100755..100644
--- a/pkg/abi/linux/linux_arm64_state_autogen.go
+++ b/pkg/abi/linux/linux_arm64_state_autogen.go
diff --git a/pkg/abi/linux/linux_state_autogen.go b/pkg/abi/linux/linux_state_autogen.go
index b8e488a11..b8e488a11 100755..100644
--- a/pkg/abi/linux/linux_state_autogen.go
+++ b/pkg/abi/linux/linux_state_autogen.go
diff --git a/pkg/abi/linux/ptrace_amd64.go b/pkg/abi/linux/ptrace_amd64.go
index ed3881e27..ed3881e27 100755..100644
--- a/pkg/abi/linux/ptrace_amd64.go
+++ b/pkg/abi/linux/ptrace_amd64.go
diff --git a/pkg/abi/linux/ptrace_arm64.go b/pkg/abi/linux/ptrace_arm64.go
index 6147738b3..6147738b3 100755..100644
--- a/pkg/abi/linux/ptrace_arm64.go
+++ b/pkg/abi/linux/ptrace_arm64.go
diff --git a/pkg/abi/linux/rseq.go b/pkg/abi/linux/rseq.go
index 76253ba30..76253ba30 100755..100644
--- a/pkg/abi/linux/rseq.go
+++ b/pkg/abi/linux/rseq.go
diff --git a/pkg/abi/linux/signalfd.go b/pkg/abi/linux/signalfd.go
index 85fad9956..85fad9956 100755..100644
--- a/pkg/abi/linux/signalfd.go
+++ b/pkg/abi/linux/signalfd.go
diff --git a/pkg/abi/linux/xattr.go b/pkg/abi/linux/xattr.go
index 99180b208..99180b208 100755..100644
--- a/pkg/abi/linux/xattr.go
+++ b/pkg/abi/linux/xattr.go
diff --git a/pkg/amutex/amutex_state_autogen.go b/pkg/amutex/amutex_state_autogen.go
index 5a09c71ed..5a09c71ed 100755..100644
--- a/pkg/amutex/amutex_state_autogen.go
+++ b/pkg/amutex/amutex_state_autogen.go
diff --git a/pkg/atomicbitops/atomicbitops.go b/pkg/atomicbitops/atomicbitops.go
index 1be081719..1be081719 100755..100644
--- a/pkg/atomicbitops/atomicbitops.go
+++ b/pkg/atomicbitops/atomicbitops.go
diff --git a/pkg/atomicbitops/atomicbitops_amd64.s b/pkg/atomicbitops/atomicbitops_amd64.s
index 54c887ee5..54c887ee5 100755..100644
--- a/pkg/atomicbitops/atomicbitops_amd64.s
+++ b/pkg/atomicbitops/atomicbitops_amd64.s
diff --git a/pkg/atomicbitops/atomicbitops_arm64.s b/pkg/atomicbitops/atomicbitops_arm64.s
index 5c780851b..5c780851b 100755..100644
--- a/pkg/atomicbitops/atomicbitops_arm64.s
+++ b/pkg/atomicbitops/atomicbitops_arm64.s
diff --git a/pkg/atomicbitops/atomicbitops_noasm.go b/pkg/atomicbitops/atomicbitops_noasm.go
index 3b2898256..3b2898256 100755..100644
--- a/pkg/atomicbitops/atomicbitops_noasm.go
+++ b/pkg/atomicbitops/atomicbitops_noasm.go
diff --git a/pkg/atomicbitops/atomicbitops_state_autogen.go b/pkg/atomicbitops/atomicbitops_state_autogen.go
index 06fcf712a..06fcf712a 100755..100644
--- a/pkg/atomicbitops/atomicbitops_state_autogen.go
+++ b/pkg/atomicbitops/atomicbitops_state_autogen.go
diff --git a/pkg/binary/binary_state_autogen.go b/pkg/binary/binary_state_autogen.go
index 4661a5982..4661a5982 100755..100644
--- a/pkg/binary/binary_state_autogen.go
+++ b/pkg/binary/binary_state_autogen.go
diff --git a/pkg/bits/bits32.go b/pkg/bits/bits32.go
index 28134a9e7..28134a9e7 100755..100644
--- a/pkg/bits/bits32.go
+++ b/pkg/bits/bits32.go
diff --git a/pkg/bits/bits64.go b/pkg/bits/bits64.go
index 73117b19b..73117b19b 100755..100644
--- a/pkg/bits/bits64.go
+++ b/pkg/bits/bits64.go
diff --git a/pkg/bits/bits_state_autogen.go b/pkg/bits/bits_state_autogen.go
index 22b8250c6..22b8250c6 100755..100644
--- a/pkg/bits/bits_state_autogen.go
+++ b/pkg/bits/bits_state_autogen.go
diff --git a/pkg/bits/uint64_arch.go b/pkg/bits/uint64_arch.go
index 9f23eff77..9f23eff77 100755..100644
--- a/pkg/bits/uint64_arch.go
+++ b/pkg/bits/uint64_arch.go
diff --git a/pkg/bits/uint64_arch_arm64_asm.s b/pkg/bits/uint64_arch_arm64_asm.s
index 814ba562d..814ba562d 100755..100644
--- a/pkg/bits/uint64_arch_arm64_asm.s
+++ b/pkg/bits/uint64_arch_arm64_asm.s
diff --git a/pkg/bpf/bpf_state_autogen.go b/pkg/bpf/bpf_state_autogen.go
index ae8a36d57..ae8a36d57 100755..100644
--- a/pkg/bpf/bpf_state_autogen.go
+++ b/pkg/bpf/bpf_state_autogen.go
diff --git a/pkg/buffer/buffer.go b/pkg/buffer/buffer.go
index c6d089fd9..c6d089fd9 100755..100644
--- a/pkg/buffer/buffer.go
+++ b/pkg/buffer/buffer.go
diff --git a/pkg/buffer/buffer_list.go b/pkg/buffer/buffer_list.go
index 15c7a74cc..15c7a74cc 100755..100644
--- a/pkg/buffer/buffer_list.go
+++ b/pkg/buffer/buffer_list.go
diff --git a/pkg/buffer/buffer_state_autogen.go b/pkg/buffer/buffer_state_autogen.go
index 2e6299f81..2e6299f81 100755..100644
--- a/pkg/buffer/buffer_state_autogen.go
+++ b/pkg/buffer/buffer_state_autogen.go
diff --git a/pkg/buffer/buffer_unsafe_state_autogen.go b/pkg/buffer/buffer_unsafe_state_autogen.go
index 5a5c40722..5a5c40722 100755..100644
--- a/pkg/buffer/buffer_unsafe_state_autogen.go
+++ b/pkg/buffer/buffer_unsafe_state_autogen.go
diff --git a/pkg/buffer/safemem.go b/pkg/buffer/safemem.go
index 0e5b86344..b789e56e9 100755..100644
--- a/pkg/buffer/safemem.go
+++ b/pkg/buffer/safemem.go
@@ -28,12 +28,11 @@ func (b *buffer) ReadBlock() safemem.Block {
 	return safemem.BlockFromSafeSlice(b.ReadSlice())
 }
 
-// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
-//
-// This will advance the write index.
-func (v *View) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
-	need := int(srcs.NumBytes())
-	if need == 0 {
+// WriteFromSafememReader writes up to count bytes from r to v and advances the
+// write index by the number of bytes written. It calls r.ReadToBlocks() at
+// most once.
+func (v *View) WriteFromSafememReader(r safemem.Reader, count uint64) (uint64, error) {
+	if count == 0 {
 		return 0, nil
 	}
 
@@ -50,32 +49,33 @@ func (v *View) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
 	}
 
 	// Does the last block have sufficient capacity alone?
-	if l := firstBuf.WriteSize(); l >= need {
-		dst = safemem.BlockSeqOf(firstBuf.WriteBlock())
+	if l := uint64(firstBuf.WriteSize()); l >= count {
+		dst = safemem.BlockSeqOf(firstBuf.WriteBlock().TakeFirst64(count))
 	} else {
 		// Append blocks until sufficient.
-		need -= l
+		count -= l
 		blocks = append(blocks, firstBuf.WriteBlock())
-		for need > 0 {
+		for count > 0 {
 			emptyBuf := bufferPool.Get().(*buffer)
 			v.data.PushBack(emptyBuf)
-			need -= emptyBuf.WriteSize()
-			blocks = append(blocks, emptyBuf.WriteBlock())
+			block := emptyBuf.WriteBlock().TakeFirst64(count)
+			count -= uint64(block.Len())
+			blocks = append(blocks, block)
 		}
 		dst = safemem.BlockSeqFromSlice(blocks)
 	}
 
-	// Perform the copy.
-	n, err := safemem.CopySeq(dst, srcs)
+	// Perform I/O.
+	n, err := r.ReadToBlocks(dst)
 	v.size += int64(n)
 
 	// Update all indices.
-	for left := int(n); left > 0; firstBuf = firstBuf.Next() {
-		if l := firstBuf.WriteSize(); left >= l {
+	for left := n; left > 0; firstBuf = firstBuf.Next() {
+		if l := firstBuf.WriteSize(); left >= uint64(l) {
 			firstBuf.WriteMove(l) // Whole block.
-			left -= l
+			left -= uint64(l)
 		} else {
-			firstBuf.WriteMove(left) // Partial block.
+			firstBuf.WriteMove(int(left)) // Partial block.
 			left = 0
 		}
 	}
@@ -83,14 +83,16 @@ func (v *View) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
 	return n, err
 }
 
-// ReadToBlocks implements safemem.Reader.ReadToBlocks.
-//
-// This will not advance the read index; the caller should follow
-// this call with a call to TrimFront in order to remove the read
-// data from the buffer. This is done to support pipe sematics.
-func (v *View) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
-	need := int(dsts.NumBytes())
-	if need == 0 {
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks. It advances the
+// write index by the number of bytes written.
+func (v *View) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
+	return v.WriteFromSafememReader(&safemem.BlockSeqReader{srcs}, srcs.NumBytes())
+}
+
+// ReadToSafememWriter reads up to count bytes from v to w. It does not advance
+// the read index. It calls w.WriteFromBlocks() at most once.
+func (v *View) ReadToSafememWriter(w safemem.Writer, count uint64) (uint64, error) {
+	if count == 0 {
 		return 0, nil
 	}
 
@@ -105,25 +107,27 @@ func (v *View) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
 	}
 
 	// Is all the data in a single block?
-	if l := firstBuf.ReadSize(); l >= need {
-		src = safemem.BlockSeqOf(firstBuf.ReadBlock())
+	if l := uint64(firstBuf.ReadSize()); l >= count {
+		src = safemem.BlockSeqOf(firstBuf.ReadBlock().TakeFirst64(count))
 	} else {
 		// Build a list of all the buffers.
-		need -= l
+		count -= l
 		blocks = append(blocks, firstBuf.ReadBlock())
-		for buf := firstBuf.Next(); buf != nil && need > 0; buf = buf.Next() {
-			need -= buf.ReadSize()
-			blocks = append(blocks, buf.ReadBlock())
+		for buf := firstBuf.Next(); buf != nil && count > 0; buf = buf.Next() {
+			block := buf.ReadBlock().TakeFirst64(count)
+			count -= uint64(block.Len())
+			blocks = append(blocks, block)
 		}
 		src = safemem.BlockSeqFromSlice(blocks)
 	}
 
-	// Perform the copy.
-	n, err := safemem.CopySeq(dsts, src)
-
-	// See above: we would normally advance the read index here, but we
-	// don't do that in order to support pipe semantics. We rely on a
-	// separate call to TrimFront() in this case.
+	// Perform I/O. As documented, we don't advance the read index.
+	return w.WriteFromBlocks(src)
+}
 
-	return n, err
+// ReadToBlocks implements safemem.Reader.ReadToBlocks. It does not advance the
+// read index by the number of bytes read, such that it's only safe to call if
+// the caller guarantees that ReadToBlocks will only be called once.
+func (v *View) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
+	return v.ReadToSafememWriter(&safemem.BlockSeqWriter{dsts}, dsts.NumBytes())
 }
diff --git a/pkg/buffer/view.go b/pkg/buffer/view.go
index e6901eadb..e6901eadb 100755..100644
--- a/pkg/buffer/view.go
+++ b/pkg/buffer/view.go
diff --git a/pkg/buffer/view_unsafe.go b/pkg/buffer/view_unsafe.go
index d1ef39b26..d1ef39b26 100755..100644
--- a/pkg/buffer/view_unsafe.go
+++ b/pkg/buffer/view_unsafe.go
diff --git a/pkg/compressio/compressio_state_autogen.go b/pkg/compressio/compressio_state_autogen.go
index c47e0dd17..c47e0dd17 100755..100644
--- a/pkg/compressio/compressio_state_autogen.go
+++ b/pkg/compressio/compressio_state_autogen.go
diff --git a/pkg/context/context.go b/pkg/context/context.go
index 5319b6d8d..5319b6d8d 100755..100644
--- a/pkg/context/context.go
+++ b/pkg/context/context.go
diff --git a/pkg/context/context_state_autogen.go b/pkg/context/context_state_autogen.go
index fdc3c9fbb..fdc3c9fbb 100755..100644
--- a/pkg/context/context_state_autogen.go
+++ b/pkg/context/context_state_autogen.go
diff --git a/pkg/control/client/client_state_autogen.go b/pkg/control/client/client_state_autogen.go
index 9872f1107..9872f1107 100755..100644
--- a/pkg/control/client/client_state_autogen.go
+++ b/pkg/control/client/client_state_autogen.go
diff --git a/pkg/control/server/server_state_autogen.go b/pkg/control/server/server_state_autogen.go
index c236b8da5..c236b8da5 100755..100644
--- a/pkg/control/server/server_state_autogen.go
+++ b/pkg/control/server/server_state_autogen.go
diff --git a/pkg/cpuid/cpuid_arm64.go b/pkg/cpuid/cpuid_arm64.go
index 08381c1c0..08381c1c0 100755..100644
--- a/pkg/cpuid/cpuid_arm64.go
+++ b/pkg/cpuid/cpuid_arm64.go
diff --git a/pkg/cpuid/cpuid_arm64_state_autogen.go b/pkg/cpuid/cpuid_arm64_state_autogen.go
index 0e671d441..0e671d441 100755..100644
--- a/pkg/cpuid/cpuid_arm64_state_autogen.go
+++ b/pkg/cpuid/cpuid_arm64_state_autogen.go
diff --git a/pkg/cpuid/cpuid_state_autogen.go b/pkg/cpuid/cpuid_state_autogen.go
index 86206a6bf..86206a6bf 100755..100644
--- a/pkg/cpuid/cpuid_state_autogen.go
+++ b/pkg/cpuid/cpuid_state_autogen.go
diff --git a/pkg/cpuid/cpuid_x86.go b/pkg/cpuid/cpuid_x86.go
index 562f8f405..562f8f405 100755..100644
--- a/pkg/cpuid/cpuid_x86.go
+++ b/pkg/cpuid/cpuid_x86.go
diff --git a/pkg/cpuid/cpuid_x86_state_autogen.go b/pkg/cpuid/cpuid_x86_state_autogen.go
index 591868c88..591868c88 100755..100644
--- a/pkg/cpuid/cpuid_x86_state_autogen.go
+++ b/pkg/cpuid/cpuid_x86_state_autogen.go
diff --git a/pkg/eventchannel/eventchannel_go_proto/event.pb.go b/pkg/eventchannel/eventchannel_go_proto/event.pb.go
index bb71ed3e6..bb71ed3e6 100755..100644
--- a/pkg/eventchannel/eventchannel_go_proto/event.pb.go
+++ b/pkg/eventchannel/eventchannel_go_proto/event.pb.go
diff --git a/pkg/eventchannel/eventchannel_state_autogen.go b/pkg/eventchannel/eventchannel_state_autogen.go
index 50b9c54b3..50b9c54b3 100755..100644
--- a/pkg/eventchannel/eventchannel_state_autogen.go
+++ b/pkg/eventchannel/eventchannel_state_autogen.go
diff --git a/pkg/fd/fd_state_autogen.go b/pkg/fd/fd_state_autogen.go
index 5ad412976..5ad412976 100755..100644
--- a/pkg/fd/fd_state_autogen.go
+++ b/pkg/fd/fd_state_autogen.go
diff --git a/pkg/fdchannel/fdchannel_unsafe.go b/pkg/fdchannel/fdchannel_unsafe.go
index 367235be5..367235be5 100755..100644
--- a/pkg/fdchannel/fdchannel_unsafe.go
+++ b/pkg/fdchannel/fdchannel_unsafe.go
diff --git a/pkg/fdchannel/fdchannel_unsafe_state_autogen.go b/pkg/fdchannel/fdchannel_unsafe_state_autogen.go
index 61447d773..61447d773 100755..100644
--- a/pkg/fdchannel/fdchannel_unsafe_state_autogen.go
+++ b/pkg/fdchannel/fdchannel_unsafe_state_autogen.go
diff --git a/pkg/fdnotifier/fdnotifier_state_autogen.go b/pkg/fdnotifier/fdnotifier_state_autogen.go
index 527d44091..527d44091 100755..100644
--- a/pkg/fdnotifier/fdnotifier_state_autogen.go
+++ b/pkg/fdnotifier/fdnotifier_state_autogen.go
diff --git a/pkg/fdnotifier/fdnotifier_unsafe_state_autogen.go b/pkg/fdnotifier/fdnotifier_unsafe_state_autogen.go
index 527d44091..527d44091 100755..100644
--- a/pkg/fdnotifier/fdnotifier_unsafe_state_autogen.go
+++ b/pkg/fdnotifier/fdnotifier_unsafe_state_autogen.go
diff --git a/pkg/flipcall/ctrl_futex.go b/pkg/flipcall/ctrl_futex.go
index e7c3a3a0b..e7c3a3a0b 100755..100644
--- a/pkg/flipcall/ctrl_futex.go
+++ b/pkg/flipcall/ctrl_futex.go
diff --git a/pkg/flipcall/flipcall.go b/pkg/flipcall/flipcall.go
index 3cdb576e1..3cdb576e1 100755..100644
--- a/pkg/flipcall/flipcall.go
+++ b/pkg/flipcall/flipcall.go
diff --git a/pkg/flipcall/flipcall_linux_state_autogen.go b/pkg/flipcall/flipcall_linux_state_autogen.go
index ce37ac4e1..ce37ac4e1 100755..100644
--- a/pkg/flipcall/flipcall_linux_state_autogen.go
+++ b/pkg/flipcall/flipcall_linux_state_autogen.go
diff --git a/pkg/flipcall/flipcall_state_autogen.go b/pkg/flipcall/flipcall_state_autogen.go
index 0e03c2a65..0e03c2a65 100755..100644
--- a/pkg/flipcall/flipcall_state_autogen.go
+++ b/pkg/flipcall/flipcall_state_autogen.go
diff --git a/pkg/flipcall/flipcall_unsafe.go b/pkg/flipcall/flipcall_unsafe.go
index ac974b232..ac974b232 100755..100644
--- a/pkg/flipcall/flipcall_unsafe.go
+++ b/pkg/flipcall/flipcall_unsafe.go
diff --git a/pkg/flipcall/flipcall_unsafe_state_autogen.go b/pkg/flipcall/flipcall_unsafe_state_autogen.go
index 0e03c2a65..0e03c2a65 100755..100644
--- a/pkg/flipcall/flipcall_unsafe_state_autogen.go
+++ b/pkg/flipcall/flipcall_unsafe_state_autogen.go
diff --git a/pkg/flipcall/futex_linux.go b/pkg/flipcall/futex_linux.go
index 168c1ccff..168c1ccff 100755..100644
--- a/pkg/flipcall/futex_linux.go
+++ b/pkg/flipcall/futex_linux.go
diff --git a/pkg/flipcall/io.go b/pkg/flipcall/io.go
index 85e40b932..85e40b932 100755..100644
--- a/pkg/flipcall/io.go
+++ b/pkg/flipcall/io.go
diff --git a/pkg/flipcall/packet_window_allocator.go b/pkg/flipcall/packet_window_allocator.go
index af9cc3d21..af9cc3d21 100755..100644
--- a/pkg/flipcall/packet_window_allocator.go
+++ b/pkg/flipcall/packet_window_allocator.go
diff --git a/pkg/fspath/builder.go b/pkg/fspath/builder.go
index 6318d3874..6318d3874 100755..100644
--- a/pkg/fspath/builder.go
+++ b/pkg/fspath/builder.go
diff --git a/pkg/fspath/fspath.go b/pkg/fspath/fspath.go
index 4c983d5fd..4c983d5fd 100755..100644
--- a/pkg/fspath/fspath.go
+++ b/pkg/fspath/fspath.go
diff --git a/pkg/fspath/fspath_state_autogen.go b/pkg/fspath/fspath_state_autogen.go
index 6ceea8003..6ceea8003 100755..100644
--- a/pkg/fspath/fspath_state_autogen.go
+++ b/pkg/fspath/fspath_state_autogen.go
diff --git a/pkg/gate/gate_state_autogen.go b/pkg/gate/gate_state_autogen.go
index 221af659e..221af659e 100755..100644
--- a/pkg/gate/gate_state_autogen.go
+++ b/pkg/gate/gate_state_autogen.go
diff --git a/pkg/gohacks/gohacks_unsafe.go b/pkg/gohacks/gohacks_unsafe.go
index aad675172..aad675172 100755..100644
--- a/pkg/gohacks/gohacks_unsafe.go
+++ b/pkg/gohacks/gohacks_unsafe.go
diff --git a/pkg/gohacks/gohacks_unsafe_state_autogen.go b/pkg/gohacks/gohacks_unsafe_state_autogen.go
index c651ff01e..c651ff01e 100755..100644
--- a/pkg/gohacks/gohacks_unsafe_state_autogen.go
+++ b/pkg/gohacks/gohacks_unsafe_state_autogen.go
diff --git a/pkg/ilist/ilist_state_autogen.go b/pkg/ilist/ilist_state_autogen.go
index 4294bcb90..4294bcb90 100755..100644
--- a/pkg/ilist/ilist_state_autogen.go
+++ b/pkg/ilist/ilist_state_autogen.go
diff --git a/pkg/ilist/interface_list.go b/pkg/ilist/interface_list.go
index cabf46e3f..cabf46e3f 100755..100644
--- a/pkg/ilist/interface_list.go
+++ b/pkg/ilist/interface_list.go
diff --git a/pkg/linewriter/linewriter_state_autogen.go b/pkg/linewriter/linewriter_state_autogen.go
deleted file mode 100755
index 1cd1df9b8..000000000
--- a/pkg/linewriter/linewriter_state_autogen.go
+++ /dev/null
@@ -1,3 +0,0 @@
-// automatically generated by stateify.
-
-package linewriter
diff --git a/pkg/memutil/memutil_unsafe_state_autogen.go b/pkg/memutil/memutil_unsafe_state_autogen.go
index 173297149..173297149 100755..100644
--- a/pkg/memutil/memutil_unsafe_state_autogen.go
+++ b/pkg/memutil/memutil_unsafe_state_autogen.go
diff --git a/pkg/metric/metric_go_proto/metric.pb.go b/pkg/metric/metric_go_proto/metric.pb.go
index 13f41a80d..13f41a80d 100755..100644
--- a/pkg/metric/metric_go_proto/metric.pb.go
+++ b/pkg/metric/metric_go_proto/metric.pb.go
diff --git a/pkg/metric/metric_state_autogen.go b/pkg/metric/metric_state_autogen.go
index 36e5ed81b..36e5ed81b 100755..100644
--- a/pkg/metric/metric_state_autogen.go
+++ b/pkg/metric/metric_state_autogen.go
diff --git a/pkg/p9/p9_state_autogen.go b/pkg/p9/p9_state_autogen.go
index bc9b1bd57..bc9b1bd57 100755..100644
--- a/pkg/p9/p9_state_autogen.go
+++ b/pkg/p9/p9_state_autogen.go
diff --git a/pkg/p9/transport_flipcall.go b/pkg/p9/transport_flipcall.go
index 38038abdf..38038abdf 100755..100644
--- a/pkg/p9/transport_flipcall.go
+++ b/pkg/p9/transport_flipcall.go
diff --git a/pkg/pool/pool.go b/pkg/pool/pool.go
index a1b2e0cfe..a1b2e0cfe 100755..100644
--- a/pkg/pool/pool.go
+++ b/pkg/pool/pool.go
diff --git a/pkg/pool/pool_state_autogen.go b/pkg/pool/pool_state_autogen.go
index 1f4164c00..1f4164c00 100755..100644
--- a/pkg/pool/pool_state_autogen.go
+++ b/pkg/pool/pool_state_autogen.go
diff --git a/pkg/procid/procid_state_autogen.go b/pkg/procid/procid_state_autogen.go
index 662988d79..662988d79 100755..100644
--- a/pkg/procid/procid_state_autogen.go
+++ b/pkg/procid/procid_state_autogen.go
diff --git a/pkg/rand/rand_linux_state_autogen.go b/pkg/rand/rand_linux_state_autogen.go
index f727c9314..f727c9314 100755..100644
--- a/pkg/rand/rand_linux_state_autogen.go
+++ b/pkg/rand/rand_linux_state_autogen.go
diff --git a/pkg/rand/rand_state_autogen.go b/pkg/rand/rand_state_autogen.go
index e0a5cd184..e0a5cd184 100755..100644
--- a/pkg/rand/rand_state_autogen.go
+++ b/pkg/rand/rand_state_autogen.go
diff --git a/pkg/refs/refs_state_autogen.go b/pkg/refs/refs_state_autogen.go
index 4c5591d30..4c5591d30 100755..100644
--- a/pkg/refs/refs_state_autogen.go
+++ b/pkg/refs/refs_state_autogen.go
diff --git a/pkg/refs/weak_ref_list.go b/pkg/refs/weak_ref_list.go
index 90433fb28..90433fb28 100755..100644
--- a/pkg/refs/weak_ref_list.go
+++ b/pkg/refs/weak_ref_list.go
diff --git a/pkg/safecopy/atomic_amd64.s b/pkg/safecopy/atomic_amd64.s
index a0cd78f33..a0cd78f33 100755..100644
--- a/pkg/safecopy/atomic_amd64.s
+++ b/pkg/safecopy/atomic_amd64.s
diff --git a/pkg/safecopy/atomic_arm64.s b/pkg/safecopy/atomic_arm64.s
index d58ed71f7..d58ed71f7 100755..100644
--- a/pkg/safecopy/atomic_arm64.s
+++ b/pkg/safecopy/atomic_arm64.s
diff --git a/pkg/safecopy/memclr_amd64.s b/pkg/safecopy/memclr_amd64.s
index 64cf32f05..64cf32f05 100755..100644
--- a/pkg/safecopy/memclr_amd64.s
+++ b/pkg/safecopy/memclr_amd64.s
diff --git a/pkg/safecopy/memclr_arm64.s b/pkg/safecopy/memclr_arm64.s
index 7361b9067..7361b9067 100755..100644
--- a/pkg/safecopy/memclr_arm64.s
+++ b/pkg/safecopy/memclr_arm64.s
diff --git a/pkg/safecopy/memcpy_amd64.s b/pkg/safecopy/memcpy_amd64.s
index 00b46c18f..00b46c18f 100755..100644
--- a/pkg/safecopy/memcpy_amd64.s
+++ b/pkg/safecopy/memcpy_amd64.s
diff --git a/pkg/safecopy/memcpy_arm64.s b/pkg/safecopy/memcpy_arm64.s
index e7e541565..e7e541565 100755..100644
--- a/pkg/safecopy/memcpy_arm64.s
+++ b/pkg/safecopy/memcpy_arm64.s
diff --git a/pkg/safecopy/safecopy.go b/pkg/safecopy/safecopy.go
index 2fb7e5809..2fb7e5809 100755..100644
--- a/pkg/safecopy/safecopy.go
+++ b/pkg/safecopy/safecopy.go
diff --git a/pkg/safecopy/safecopy_state_autogen.go b/pkg/safecopy/safecopy_state_autogen.go
index 791eef959..791eef959 100755..100644
--- a/pkg/safecopy/safecopy_state_autogen.go
+++ b/pkg/safecopy/safecopy_state_autogen.go
diff --git a/pkg/safecopy/safecopy_unsafe.go b/pkg/safecopy/safecopy_unsafe.go
index 41dd567f3..41dd567f3 100755..100644
--- a/pkg/safecopy/safecopy_unsafe.go
+++ b/pkg/safecopy/safecopy_unsafe.go
diff --git a/pkg/safecopy/safecopy_unsafe_state_autogen.go b/pkg/safecopy/safecopy_unsafe_state_autogen.go
index 791eef959..791eef959 100755..100644
--- a/pkg/safecopy/safecopy_unsafe_state_autogen.go
+++ b/pkg/safecopy/safecopy_unsafe_state_autogen.go
diff --git a/pkg/safecopy/sighandler_amd64.s b/pkg/safecopy/sighandler_amd64.s
index 475ae48e9..475ae48e9 100755..100644
--- a/pkg/safecopy/sighandler_amd64.s
+++ b/pkg/safecopy/sighandler_amd64.s
diff --git a/pkg/safecopy/sighandler_arm64.s b/pkg/safecopy/sighandler_arm64.s
index 53e4ac2c1..53e4ac2c1 100755..100644
--- a/pkg/safecopy/sighandler_arm64.s
+++ b/pkg/safecopy/sighandler_arm64.s
diff --git a/pkg/safemem/block_unsafe.go b/pkg/safemem/block_unsafe.go
index e7fd30743..e7fd30743 100755..100644
--- a/pkg/safemem/block_unsafe.go
+++ b/pkg/safemem/block_unsafe.go
diff --git a/pkg/safemem/io.go b/pkg/safemem/io.go
index f039a5c34..f039a5c34 100755..100644
--- a/pkg/safemem/io.go
+++ b/pkg/safemem/io.go
diff --git a/pkg/safemem/safemem.go b/pkg/safemem/safemem.go
index 3e70d33a2..3e70d33a2 100755..100644
--- a/pkg/safemem/safemem.go
+++ b/pkg/safemem/safemem.go
diff --git a/pkg/safemem/safemem_state_autogen.go b/pkg/safemem/safemem_state_autogen.go
index 66d53f22d..66d53f22d 100755..100644
--- a/pkg/safemem/safemem_state_autogen.go
+++ b/pkg/safemem/safemem_state_autogen.go
diff --git a/pkg/safemem/safemem_unsafe_state_autogen.go b/pkg/safemem/safemem_unsafe_state_autogen.go
index 66d53f22d..66d53f22d 100755..100644
--- a/pkg/safemem/safemem_unsafe_state_autogen.go
+++ b/pkg/safemem/safemem_unsafe_state_autogen.go
diff --git a/pkg/safemem/seq_unsafe.go b/pkg/safemem/seq_unsafe.go
index f5f0574f8..f5f0574f8 100755..100644
--- a/pkg/safemem/seq_unsafe.go
+++ b/pkg/safemem/seq_unsafe.go
diff --git a/pkg/seccomp/seccomp_amd64_state_autogen.go b/pkg/seccomp/seccomp_amd64_state_autogen.go
index 27a96018b..27a96018b 100755..100644
--- a/pkg/seccomp/seccomp_amd64_state_autogen.go
+++ b/pkg/seccomp/seccomp_amd64_state_autogen.go
diff --git a/pkg/seccomp/seccomp_arm64_state_autogen.go b/pkg/seccomp/seccomp_arm64_state_autogen.go
index 96c64c23d..96c64c23d 100755..100644
--- a/pkg/seccomp/seccomp_arm64_state_autogen.go
+++ b/pkg/seccomp/seccomp_arm64_state_autogen.go
diff --git a/pkg/seccomp/seccomp_state_autogen.go b/pkg/seccomp/seccomp_state_autogen.go
index e16b5d7c2..e16b5d7c2 100755..100644
--- a/pkg/seccomp/seccomp_state_autogen.go
+++ b/pkg/seccomp/seccomp_state_autogen.go
diff --git a/pkg/seccomp/seccomp_unsafe_state_autogen.go b/pkg/seccomp/seccomp_unsafe_state_autogen.go
index e16b5d7c2..e16b5d7c2 100755..100644
--- a/pkg/seccomp/seccomp_unsafe_state_autogen.go
+++ b/pkg/seccomp/seccomp_unsafe_state_autogen.go
diff --git a/pkg/secio/secio_state_autogen.go b/pkg/secio/secio_state_autogen.go
index 372ac4b92..372ac4b92 100755..100644
--- a/pkg/secio/secio_state_autogen.go
+++ b/pkg/secio/secio_state_autogen.go
diff --git a/pkg/sentry/arch/arch_aarch64.go b/pkg/sentry/arch/arch_aarch64.go
index 343f81f59..343f81f59 100755..100644
--- a/pkg/sentry/arch/arch_aarch64.go
+++ b/pkg/sentry/arch/arch_aarch64.go
diff --git a/pkg/sentry/arch/arch_aarch64_abi_autogen_unsafe.go b/pkg/sentry/arch/arch_aarch64_abi_autogen_unsafe.go
index f7a3597d4..f7a3597d4 100755..100644
--- a/pkg/sentry/arch/arch_aarch64_abi_autogen_unsafe.go
+++ b/pkg/sentry/arch/arch_aarch64_abi_autogen_unsafe.go
diff --git a/pkg/sentry/arch/arch_aarch64_state_autogen.go b/pkg/sentry/arch/arch_aarch64_state_autogen.go
index 49f2e3d67..49f2e3d67 100755..100644
--- a/pkg/sentry/arch/arch_aarch64_state_autogen.go
+++ b/pkg/sentry/arch/arch_aarch64_state_autogen.go
diff --git a/pkg/sentry/arch/arch_abi_autogen_unsafe.go b/pkg/sentry/arch/arch_abi_autogen_unsafe.go
index 98cc11f75..98cc11f75 100755..100644
--- a/pkg/sentry/arch/arch_abi_autogen_unsafe.go
+++ b/pkg/sentry/arch/arch_abi_autogen_unsafe.go
diff --git a/pkg/sentry/arch/arch_amd64_abi_autogen_unsafe.go b/pkg/sentry/arch/arch_amd64_abi_autogen_unsafe.go
index 8eadb6e22..8eadb6e22 100755..100644
--- a/pkg/sentry/arch/arch_amd64_abi_autogen_unsafe.go
+++ b/pkg/sentry/arch/arch_amd64_abi_autogen_unsafe.go
diff --git a/pkg/sentry/arch/arch_amd64_state_autogen.go b/pkg/sentry/arch/arch_amd64_state_autogen.go
index 73c523c90..73c523c90 100755..100644
--- a/pkg/sentry/arch/arch_amd64_state_autogen.go
+++ b/pkg/sentry/arch/arch_amd64_state_autogen.go
diff --git a/pkg/sentry/arch/arch_arm64.go b/pkg/sentry/arch/arch_arm64.go
index ada7ac7b8..ada7ac7b8 100755..100644
--- a/pkg/sentry/arch/arch_arm64.go
+++ b/pkg/sentry/arch/arch_arm64.go
diff --git a/pkg/sentry/arch/arch_arm64_abi_autogen_unsafe.go b/pkg/sentry/arch/arch_arm64_abi_autogen_unsafe.go
index c8e4c7c24..c8e4c7c24 100755..100644
--- a/pkg/sentry/arch/arch_arm64_abi_autogen_unsafe.go
+++ b/pkg/sentry/arch/arch_arm64_abi_autogen_unsafe.go
diff --git a/pkg/sentry/arch/arch_arm64_state_autogen.go b/pkg/sentry/arch/arch_arm64_state_autogen.go
index 9c6dfdf2e..9c6dfdf2e 100755..100644
--- a/pkg/sentry/arch/arch_arm64_state_autogen.go
+++ b/pkg/sentry/arch/arch_arm64_state_autogen.go
diff --git a/pkg/sentry/arch/arch_state_autogen.go b/pkg/sentry/arch/arch_state_autogen.go
index 82f4d9d73..82f4d9d73 100755..100644
--- a/pkg/sentry/arch/arch_state_autogen.go
+++ b/pkg/sentry/arch/arch_state_autogen.go
diff --git a/pkg/sentry/arch/arch_x86_abi_autogen_unsafe.go b/pkg/sentry/arch/arch_x86_abi_autogen_unsafe.go
index 521dcbb06..521dcbb06 100755..100644
--- a/pkg/sentry/arch/arch_x86_abi_autogen_unsafe.go
+++ b/pkg/sentry/arch/arch_x86_abi_autogen_unsafe.go
diff --git a/pkg/sentry/arch/arch_x86_impl.go b/pkg/sentry/arch/arch_x86_impl.go
index 0c73fcbfb..0c73fcbfb 100755..100644
--- a/pkg/sentry/arch/arch_x86_impl.go
+++ b/pkg/sentry/arch/arch_x86_impl.go
diff --git a/pkg/sentry/arch/arch_x86_impl_abi_autogen_unsafe.go b/pkg/sentry/arch/arch_x86_impl_abi_autogen_unsafe.go
index 4357dc093..4357dc093 100755..100644
--- a/pkg/sentry/arch/arch_x86_impl_abi_autogen_unsafe.go
+++ b/pkg/sentry/arch/arch_x86_impl_abi_autogen_unsafe.go
diff --git a/pkg/sentry/arch/arch_x86_impl_state_autogen.go b/pkg/sentry/arch/arch_x86_impl_state_autogen.go
index 7303bb17f..7303bb17f 100755..100644
--- a/pkg/sentry/arch/arch_x86_impl_state_autogen.go
+++ b/pkg/sentry/arch/arch_x86_impl_state_autogen.go
diff --git a/pkg/sentry/arch/arch_x86_state_autogen.go b/pkg/sentry/arch/arch_x86_state_autogen.go
index 20eaa99a6..20eaa99a6 100755..100644
--- a/pkg/sentry/arch/arch_x86_state_autogen.go
+++ b/pkg/sentry/arch/arch_x86_state_autogen.go
diff --git a/pkg/sentry/arch/registers_go_proto/registers.pb.go b/pkg/sentry/arch/registers_go_proto/registers.pb.go
index c4e9584b5..c4e9584b5 100755..100644
--- a/pkg/sentry/arch/registers_go_proto/registers.pb.go
+++ b/pkg/sentry/arch/registers_go_proto/registers.pb.go
diff --git a/pkg/sentry/arch/signal.go b/pkg/sentry/arch/signal.go
index c9fb55d00..c9fb55d00 100755..100644
--- a/pkg/sentry/arch/signal.go
+++ b/pkg/sentry/arch/signal.go
diff --git a/pkg/sentry/arch/signal_arm64.go b/pkg/sentry/arch/signal_arm64.go
index 642c79dda..642c79dda 100755..100644
--- a/pkg/sentry/arch/signal_arm64.go
+++ b/pkg/sentry/arch/signal_arm64.go
diff --git a/pkg/sentry/arch/syscalls_arm64.go b/pkg/sentry/arch/syscalls_arm64.go
index 95dfd1e90..95dfd1e90 100755..100644
--- a/pkg/sentry/arch/syscalls_arm64.go
+++ b/pkg/sentry/arch/syscalls_arm64.go
diff --git a/pkg/sentry/control/control_state_autogen.go b/pkg/sentry/control/control_state_autogen.go
index bd5797221..bd5797221 100755..100644
--- a/pkg/sentry/control/control_state_autogen.go
+++ b/pkg/sentry/control/control_state_autogen.go
diff --git a/pkg/sentry/device/device_state_autogen.go b/pkg/sentry/device/device_state_autogen.go
index dd41a5659..dd41a5659 100755..100644
--- a/pkg/sentry/device/device_state_autogen.go
+++ b/pkg/sentry/device/device_state_autogen.go
diff --git a/pkg/sentry/devices/memdev/full.go b/pkg/sentry/devices/memdev/full.go
index c7e197691..c7e197691 100755..100644
--- a/pkg/sentry/devices/memdev/full.go
+++ b/pkg/sentry/devices/memdev/full.go
diff --git a/pkg/sentry/devices/memdev/memdev.go b/pkg/sentry/devices/memdev/memdev.go
index 5759900c4..5759900c4 100755..100644
--- a/pkg/sentry/devices/memdev/memdev.go
+++ b/pkg/sentry/devices/memdev/memdev.go
diff --git a/pkg/sentry/devices/memdev/memdev_state_autogen.go b/pkg/sentry/devices/memdev/memdev_state_autogen.go
index 2676fbbe5..2676fbbe5 100755..100644
--- a/pkg/sentry/devices/memdev/memdev_state_autogen.go
+++ b/pkg/sentry/devices/memdev/memdev_state_autogen.go
diff --git a/pkg/sentry/devices/memdev/null.go b/pkg/sentry/devices/memdev/null.go
index 33d060d02..33d060d02 100755..100644
--- a/pkg/sentry/devices/memdev/null.go
+++ b/pkg/sentry/devices/memdev/null.go
diff --git a/pkg/sentry/devices/memdev/random.go b/pkg/sentry/devices/memdev/random.go
index acfa23149..acfa23149 100755..100644
--- a/pkg/sentry/devices/memdev/random.go
+++ b/pkg/sentry/devices/memdev/random.go
diff --git a/pkg/sentry/devices/memdev/zero.go b/pkg/sentry/devices/memdev/zero.go
index 3b1372b9e..3b1372b9e 100755..100644
--- a/pkg/sentry/devices/memdev/zero.go
+++ b/pkg/sentry/devices/memdev/zero.go
diff --git a/pkg/sentry/fdimport/fdimport.go b/pkg/sentry/fdimport/fdimport.go
index a4199f9e9..a4199f9e9 100755..100644
--- a/pkg/sentry/fdimport/fdimport.go
+++ b/pkg/sentry/fdimport/fdimport.go
diff --git a/pkg/sentry/fdimport/fdimport_state_autogen.go b/pkg/sentry/fdimport/fdimport_state_autogen.go
index fbb89b276..fbb89b276 100755..100644
--- a/pkg/sentry/fdimport/fdimport_state_autogen.go
+++ b/pkg/sentry/fdimport/fdimport_state_autogen.go
diff --git a/pkg/sentry/fs/anon/anon_state_autogen.go b/pkg/sentry/fs/anon/anon_state_autogen.go
index b2b1a466e..b2b1a466e 100755..100644
--- a/pkg/sentry/fs/anon/anon_state_autogen.go
+++ b/pkg/sentry/fs/anon/anon_state_autogen.go
diff --git a/pkg/sentry/fs/dev/dev_state_autogen.go b/pkg/sentry/fs/dev/dev_state_autogen.go
index 272f02672..272f02672 100755..100644
--- a/pkg/sentry/fs/dev/dev_state_autogen.go
+++ b/pkg/sentry/fs/dev/dev_state_autogen.go
diff --git a/pkg/sentry/fs/dev/net_tun.go b/pkg/sentry/fs/dev/net_tun.go
index dc7ad075a..dc7ad075a 100755..100644
--- a/pkg/sentry/fs/dev/net_tun.go
+++ b/pkg/sentry/fs/dev/net_tun.go
diff --git a/pkg/sentry/fs/dirent_list.go b/pkg/sentry/fs/dirent_list.go
index ecbbd7883..ecbbd7883 100755..100644
--- a/pkg/sentry/fs/dirent_list.go
+++ b/pkg/sentry/fs/dirent_list.go
diff --git a/pkg/sentry/fs/event_list.go b/pkg/sentry/fs/event_list.go
index 167fdf906..167fdf906 100755..100644
--- a/pkg/sentry/fs/event_list.go
+++ b/pkg/sentry/fs/event_list.go
diff --git a/pkg/sentry/fs/fdpipe/fdpipe_state_autogen.go b/pkg/sentry/fs/fdpipe/fdpipe_state_autogen.go
index 9ed7a3d41..9ed7a3d41 100755..100644
--- a/pkg/sentry/fs/fdpipe/fdpipe_state_autogen.go
+++ b/pkg/sentry/fs/fdpipe/fdpipe_state_autogen.go
diff --git a/pkg/sentry/fs/fs_state_autogen.go b/pkg/sentry/fs/fs_state_autogen.go
index 502a90d71..502a90d71 100755..100644
--- a/pkg/sentry/fs/fs_state_autogen.go
+++ b/pkg/sentry/fs/fs_state_autogen.go
diff --git a/pkg/sentry/fs/fsutil/dirty_set_impl.go b/pkg/sentry/fs/fsutil/dirty_set_impl.go
index 2510b81b3..8d462c412 100755..100644
--- a/pkg/sentry/fs/fsutil/dirty_set_impl.go
+++ b/pkg/sentry/fs/fsutil/dirty_set_impl.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const DirtytrackGaps = 0
+
+var _ = uint8(DirtytrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type DirtydynamicGap [DirtytrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *DirtydynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *DirtydynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *DirtySet) Insert(gap DirtyGapIterator, r __generics_imported0.MappableR
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (dirtySetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := DirtytrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (dirtySetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *DirtySet) Insert(gap DirtyGapIterator, r __generics_imported0.MappableR
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (dirtySetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := DirtytrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *DirtySet) InsertWithoutMerging(gap DirtyGapIterator, r __generics_impor
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *DirtySet) InsertWithoutMergingUnchecked(gap DirtyGapIterator, r __generics_imported0.MappableRange, val DirtyInfo) DirtyIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := DirtytrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return DirtyIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *DirtySet) Remove(seg DirtyIterator) DirtyGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if DirtytrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	dirtySetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if DirtytrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(DirtyGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *DirtySet) MergeUnchecked(first, second DirtyIterator) DirtyIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type Dirtynode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap DirtydynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [DirtymaxDegree - 1]__generics_imported0.MappableRange
@@ -607,12 +663,12 @@ func (n *Dirtynode) nextSibling() *Dirtynode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *Dirtynode) rebalanceBeforeInsert(gap DirtyGapIterator) DirtyGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < DirtymaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &Dirtynode{
@@ -648,6 +704,11 @@ func (n *Dirtynode) rebalanceBeforeInsert(gap DirtyGapIterator) DirtyGapIterator
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if DirtytrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *Dirtynode) rebalanceBeforeInsert(gap DirtyGapIterator) DirtyGapIterator
 	}
 	n.nrSegments = DirtyminDegree - 1
 
+	if DirtytrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *Dirtynode) rebalanceAfterRemove(gap DirtyGapIterator) DirtyGapIterator
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if DirtytrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return DirtyGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *Dirtynode) rebalanceAfterRemove(gap DirtyGapIterator) DirtyGapIterator
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if DirtytrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return DirtyGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *Dirtynode) rebalanceAfterRemove(gap DirtyGapIterator) DirtyGapIterator
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return DirtyGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *Dirtynode) rebalanceAfterRemove(gap DirtyGapIterator) DirtyGapIterator
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if DirtytrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *Dirtynode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *Dirtynode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *Dirtynode) calculateMaxGapLeaf() uint64 {
+	max := DirtyGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (DirtyGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *Dirtynode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *Dirtynode) searchFirstLargeEnoughGap(minSize uint64) DirtyGapIterator {
+	if n.maxGap.Get() < minSize {
+		return DirtyGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := DirtyGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *Dirtynode) searchLastLargeEnoughGap(minSize uint64) DirtyGapIterator {
+	if n.maxGap.Get() < minSize {
+		return DirtyGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := DirtyGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap DirtyGapIterator) NextGap() DirtyGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap DirtyGapIterator) NextLargeEnoughGap(minSize uint64) DirtyGapIterator {
+	if DirtytrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap DirtyGapIterator) nextLargeEnoughGapHelper(minSize uint64) DirtyGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return DirtyGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap DirtyGapIterator) PrevLargeEnoughGap(minSize uint64) DirtyGapIterator {
+	if DirtytrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap DirtyGapIterator) prevLargeEnoughGapHelper(minSize uint64) DirtyGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return DirtyGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *Dirtynode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if DirtytrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *DirtySet) ImportSortedSlices(sds *DirtySegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *DirtySet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.MappableRange, DirtyInfo) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *DirtySet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *DirtySet) saveRoot() *DirtySegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/fs/fsutil/file_range_set_impl.go b/pkg/sentry/fs/fsutil/file_range_set_impl.go
index 01e7a2401..e5b6d1041 100755..100644
--- a/pkg/sentry/fs/fsutil/file_range_set_impl.go
+++ b/pkg/sentry/fs/fsutil/file_range_set_impl.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const FileRangetrackGaps = 0
+
+var _ = uint8(FileRangetrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type FileRangedynamicGap [FileRangetrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *FileRangedynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *FileRangedynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *FileRangeSet) Insert(gap FileRangeGapIterator, r __generics_imported0.M
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (FileRangeSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := FileRangetrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (FileRangeSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *FileRangeSet) Insert(gap FileRangeGapIterator, r __generics_imported0.M
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (FileRangeSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := FileRangetrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *FileRangeSet) InsertWithoutMerging(gap FileRangeGapIterator, r __generi
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *FileRangeSet) InsertWithoutMergingUnchecked(gap FileRangeGapIterator, r __generics_imported0.MappableRange, val uint64) FileRangeIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := FileRangetrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return FileRangeIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *FileRangeSet) Remove(seg FileRangeIterator) FileRangeGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if FileRangetrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	FileRangeSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if FileRangetrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(FileRangeGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *FileRangeSet) MergeUnchecked(first, second FileRangeIterator) FileRange
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type FileRangenode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap FileRangedynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [FileRangemaxDegree - 1]__generics_imported0.MappableRange
@@ -607,12 +663,12 @@ func (n *FileRangenode) nextSibling() *FileRangenode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *FileRangenode) rebalanceBeforeInsert(gap FileRangeGapIterator) FileRangeGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < FileRangemaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &FileRangenode{
@@ -648,6 +704,11 @@ func (n *FileRangenode) rebalanceBeforeInsert(gap FileRangeGapIterator) FileRang
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if FileRangetrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *FileRangenode) rebalanceBeforeInsert(gap FileRangeGapIterator) FileRang
 	}
 	n.nrSegments = FileRangeminDegree - 1
 
+	if FileRangetrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *FileRangenode) rebalanceAfterRemove(gap FileRangeGapIterator) FileRange
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if FileRangetrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return FileRangeGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *FileRangenode) rebalanceAfterRemove(gap FileRangeGapIterator) FileRange
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if FileRangetrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return FileRangeGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *FileRangenode) rebalanceAfterRemove(gap FileRangeGapIterator) FileRange
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return FileRangeGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *FileRangenode) rebalanceAfterRemove(gap FileRangeGapIterator) FileRange
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if FileRangetrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *FileRangenode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *FileRangenode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *FileRangenode) calculateMaxGapLeaf() uint64 {
+	max := FileRangeGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (FileRangeGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *FileRangenode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *FileRangenode) searchFirstLargeEnoughGap(minSize uint64) FileRangeGapIterator {
+	if n.maxGap.Get() < minSize {
+		return FileRangeGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := FileRangeGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *FileRangenode) searchLastLargeEnoughGap(minSize uint64) FileRangeGapIterator {
+	if n.maxGap.Get() < minSize {
+		return FileRangeGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := FileRangeGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap FileRangeGapIterator) NextGap() FileRangeGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap FileRangeGapIterator) NextLargeEnoughGap(minSize uint64) FileRangeGapIterator {
+	if FileRangetrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap FileRangeGapIterator) nextLargeEnoughGapHelper(minSize uint64) FileRangeGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return FileRangeGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap FileRangeGapIterator) PrevLargeEnoughGap(minSize uint64) FileRangeGapIterator {
+	if FileRangetrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap FileRangeGapIterator) prevLargeEnoughGapHelper(minSize uint64) FileRangeGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return FileRangeGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *FileRangenode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if FileRangetrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *FileRangeSet) ImportSortedSlices(sds *FileRangeSegmentDataSlices) error
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *FileRangeSet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.MappableRange, uint64) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *FileRangeSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *FileRangeSet) saveRoot() *FileRangeSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/fs/fsutil/frame_ref_set.go b/pkg/sentry/fs/fsutil/frame_ref_set.go
index 6564fd0c6..dd6f5aba6 100644
--- a/pkg/sentry/fs/fsutil/frame_ref_set.go
+++ b/pkg/sentry/fs/fsutil/frame_ref_set.go
@@ -18,6 +18,7 @@ import (
 	"math"
 
 	"gvisor.dev/gvisor/pkg/sentry/platform"
+	"gvisor.dev/gvisor/pkg/sentry/usage"
 )
 
 // FrameRefSetFunctions implements segment.Functions for FrameRefSet.
@@ -49,3 +50,42 @@ func (FrameRefSetFunctions) Merge(_ platform.FileRange, val1 uint64, _ platform.
 func (FrameRefSetFunctions) Split(_ platform.FileRange, val uint64, _ uint64) (uint64, uint64) {
 	return val, val
 }
+
+// IncRefAndAccount adds a reference on the range fr. All newly inserted segments
+// are accounted as host page cache memory mappings.
+func (refs *FrameRefSet) IncRefAndAccount(fr platform.FileRange) {
+	seg, gap := refs.Find(fr.Start)
+	for {
+		switch {
+		case seg.Ok() && seg.Start() < fr.End:
+			seg = refs.Isolate(seg, fr)
+			seg.SetValue(seg.Value() + 1)
+			seg, gap = seg.NextNonEmpty()
+		case gap.Ok() && gap.Start() < fr.End:
+			newRange := gap.Range().Intersect(fr)
+			usage.MemoryAccounting.Inc(newRange.Length(), usage.Mapped)
+			seg, gap = refs.InsertWithoutMerging(gap, newRange, 1).NextNonEmpty()
+		default:
+			refs.MergeAdjacent(fr)
+			return
+		}
+	}
+}
+
+// DecRefAndAccount removes a reference on the range fr and untracks segments
+// that are removed from memory accounting.
+func (refs *FrameRefSet) DecRefAndAccount(fr platform.FileRange) {
+	seg := refs.FindSegment(fr.Start)
+
+	for seg.Ok() && seg.Start() < fr.End {
+		seg = refs.Isolate(seg, fr)
+		if old := seg.Value(); old == 1 {
+			usage.MemoryAccounting.Dec(seg.Range().Length(), usage.Mapped)
+			seg = refs.Remove(seg).NextSegment()
+		} else {
+			seg.SetValue(old - 1)
+			seg = seg.NextSegment()
+		}
+	}
+	refs.MergeAdjacent(fr)
+}
diff --git a/pkg/sentry/fs/fsutil/frame_ref_set_impl.go b/pkg/sentry/fs/fsutil/frame_ref_set_impl.go
index 88695dbd1..413b037d1 100755..100644
--- a/pkg/sentry/fs/fsutil/frame_ref_set_impl.go
+++ b/pkg/sentry/fs/fsutil/frame_ref_set_impl.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const FrameReftrackGaps = 0
+
+var _ = uint8(FrameReftrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type FrameRefdynamicGap [FrameReftrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *FrameRefdynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *FrameRefdynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *FrameRefSet) Insert(gap FrameRefGapIterator, r __generics_imported0.Fil
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (FrameRefSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := FrameReftrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (FrameRefSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *FrameRefSet) Insert(gap FrameRefGapIterator, r __generics_imported0.Fil
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (FrameRefSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := FrameReftrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *FrameRefSet) InsertWithoutMerging(gap FrameRefGapIterator, r __generics
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *FrameRefSet) InsertWithoutMergingUnchecked(gap FrameRefGapIterator, r __generics_imported0.FileRange, val uint64) FrameRefIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := FrameReftrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return FrameRefIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *FrameRefSet) Remove(seg FrameRefIterator) FrameRefGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if FrameReftrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	FrameRefSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if FrameReftrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(FrameRefGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *FrameRefSet) MergeUnchecked(first, second FrameRefIterator) FrameRefIte
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type FrameRefnode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap FrameRefdynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [FrameRefmaxDegree - 1]__generics_imported0.FileRange
@@ -607,12 +663,12 @@ func (n *FrameRefnode) nextSibling() *FrameRefnode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *FrameRefnode) rebalanceBeforeInsert(gap FrameRefGapIterator) FrameRefGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < FrameRefmaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &FrameRefnode{
@@ -648,6 +704,11 @@ func (n *FrameRefnode) rebalanceBeforeInsert(gap FrameRefGapIterator) FrameRefGa
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if FrameReftrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *FrameRefnode) rebalanceBeforeInsert(gap FrameRefGapIterator) FrameRefGa
 	}
 	n.nrSegments = FrameRefminDegree - 1
 
+	if FrameReftrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *FrameRefnode) rebalanceAfterRemove(gap FrameRefGapIterator) FrameRefGap
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if FrameReftrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return FrameRefGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *FrameRefnode) rebalanceAfterRemove(gap FrameRefGapIterator) FrameRefGap
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if FrameReftrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return FrameRefGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *FrameRefnode) rebalanceAfterRemove(gap FrameRefGapIterator) FrameRefGap
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return FrameRefGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *FrameRefnode) rebalanceAfterRemove(gap FrameRefGapIterator) FrameRefGap
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if FrameReftrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *FrameRefnode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *FrameRefnode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *FrameRefnode) calculateMaxGapLeaf() uint64 {
+	max := FrameRefGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (FrameRefGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *FrameRefnode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *FrameRefnode) searchFirstLargeEnoughGap(minSize uint64) FrameRefGapIterator {
+	if n.maxGap.Get() < minSize {
+		return FrameRefGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := FrameRefGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *FrameRefnode) searchLastLargeEnoughGap(minSize uint64) FrameRefGapIterator {
+	if n.maxGap.Get() < minSize {
+		return FrameRefGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := FrameRefGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap FrameRefGapIterator) NextGap() FrameRefGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap FrameRefGapIterator) NextLargeEnoughGap(minSize uint64) FrameRefGapIterator {
+	if FrameReftrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap FrameRefGapIterator) nextLargeEnoughGapHelper(minSize uint64) FrameRefGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return FrameRefGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap FrameRefGapIterator) PrevLargeEnoughGap(minSize uint64) FrameRefGapIterator {
+	if FrameReftrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap FrameRefGapIterator) prevLargeEnoughGapHelper(minSize uint64) FrameRefGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return FrameRefGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *FrameRefnode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if FrameReftrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *FrameRefSet) ImportSortedSlices(sds *FrameRefSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *FrameRefSet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.FileRange, uint64) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *FrameRefSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *FrameRefSet) saveRoot() *FrameRefSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/fs/fsutil/fsutil_impl_state_autogen.go b/pkg/sentry/fs/fsutil/fsutil_impl_state_autogen.go
index a0baca0c5..79d4610f0 100755..100644
--- a/pkg/sentry/fs/fsutil/fsutil_impl_state_autogen.go
+++ b/pkg/sentry/fs/fsutil/fsutil_impl_state_autogen.go
@@ -25,6 +25,7 @@ func (x *Dirtynode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -36,6 +37,7 @@ func (x *Dirtynode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
@@ -75,6 +77,7 @@ func (x *FileRangenode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -86,6 +89,7 @@ func (x *FileRangenode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
@@ -125,6 +129,7 @@ func (x *FrameRefnode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -136,6 +141,7 @@ func (x *FrameRefnode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
diff --git a/pkg/sentry/fs/fsutil/fsutil_state_autogen.go b/pkg/sentry/fs/fsutil/fsutil_state_autogen.go
index 80b93ad25..80b93ad25 100755..100644
--- a/pkg/sentry/fs/fsutil/fsutil_state_autogen.go
+++ b/pkg/sentry/fs/fsutil/fsutil_state_autogen.go
diff --git a/pkg/sentry/fs/fsutil/fsutil_unsafe_state_autogen.go b/pkg/sentry/fs/fsutil/fsutil_unsafe_state_autogen.go
index 00b0994f6..00b0994f6 100755..100644
--- a/pkg/sentry/fs/fsutil/fsutil_unsafe_state_autogen.go
+++ b/pkg/sentry/fs/fsutil/fsutil_unsafe_state_autogen.go
diff --git a/pkg/sentry/fs/gofer/fifo.go b/pkg/sentry/fs/gofer/fifo.go
index 456557058..456557058 100755..100644
--- a/pkg/sentry/fs/gofer/fifo.go
+++ b/pkg/sentry/fs/gofer/fifo.go
diff --git a/pkg/sentry/fs/gofer/gofer_state_autogen.go b/pkg/sentry/fs/gofer/gofer_state_autogen.go
index 7db9211b4..7db9211b4 100755..100644
--- a/pkg/sentry/fs/gofer/gofer_state_autogen.go
+++ b/pkg/sentry/fs/gofer/gofer_state_autogen.go
diff --git a/pkg/sentry/fs/host/host.go b/pkg/sentry/fs/host/host.go
index 081ba1dd8..081ba1dd8 100755..100644
--- a/pkg/sentry/fs/host/host.go
+++ b/pkg/sentry/fs/host/host.go
diff --git a/pkg/sentry/fs/host/host_amd64_unsafe_state_autogen.go b/pkg/sentry/fs/host/host_amd64_unsafe_state_autogen.go
index 488cbdfcf..488cbdfcf 100755..100644
--- a/pkg/sentry/fs/host/host_amd64_unsafe_state_autogen.go
+++ b/pkg/sentry/fs/host/host_amd64_unsafe_state_autogen.go
diff --git a/pkg/sentry/fs/host/host_arm64_unsafe_state_autogen.go b/pkg/sentry/fs/host/host_arm64_unsafe_state_autogen.go
index 7371b44db..7371b44db 100755..100644
--- a/pkg/sentry/fs/host/host_arm64_unsafe_state_autogen.go
+++ b/pkg/sentry/fs/host/host_arm64_unsafe_state_autogen.go
diff --git a/pkg/sentry/fs/host/host_state_autogen.go b/pkg/sentry/fs/host/host_state_autogen.go
index a6b97a154..a6b97a154 100755..100644
--- a/pkg/sentry/fs/host/host_state_autogen.go
+++ b/pkg/sentry/fs/host/host_state_autogen.go
diff --git a/pkg/sentry/fs/host/host_unsafe_state_autogen.go b/pkg/sentry/fs/host/host_unsafe_state_autogen.go
index b2d8c661f..b2d8c661f 100755..100644
--- a/pkg/sentry/fs/host/host_unsafe_state_autogen.go
+++ b/pkg/sentry/fs/host/host_unsafe_state_autogen.go
diff --git a/pkg/sentry/fs/host/util_amd64_unsafe.go b/pkg/sentry/fs/host/util_amd64_unsafe.go
index 66da6e9f5..66da6e9f5 100755..100644
--- a/pkg/sentry/fs/host/util_amd64_unsafe.go
+++ b/pkg/sentry/fs/host/util_amd64_unsafe.go
diff --git a/pkg/sentry/fs/host/util_arm64_unsafe.go b/pkg/sentry/fs/host/util_arm64_unsafe.go
index e8cb94aeb..e8cb94aeb 100755..100644
--- a/pkg/sentry/fs/host/util_arm64_unsafe.go
+++ b/pkg/sentry/fs/host/util_arm64_unsafe.go
diff --git a/pkg/sentry/fs/lock/lock_range.go b/pkg/sentry/fs/lock/lock_range.go
index 7a6f77640..7a6f77640 100755..100644
--- a/pkg/sentry/fs/lock/lock_range.go
+++ b/pkg/sentry/fs/lock/lock_range.go
diff --git a/pkg/sentry/fs/lock/lock_set.go b/pkg/sentry/fs/lock/lock_set.go
index 2343ca0b4..5356f5791 100755..100644
--- a/pkg/sentry/fs/lock/lock_set.go
+++ b/pkg/sentry/fs/lock/lock_set.go
@@ -5,6 +5,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const LocktrackGaps = 0
+
+var _ = uint8(LocktrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type LockdynamicGap [LocktrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *LockdynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *LockdynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -263,8 +291,12 @@ func (s *LockSet) Insert(gap LockGapIterator, r LockRange, val Lock) LockIterato
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (lockSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := LocktrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (lockSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -278,11 +310,16 @@ func (s *LockSet) Insert(gap LockGapIterator, r LockRange, val Lock) LockIterato
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (lockSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := LocktrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -309,11 +346,15 @@ func (s *LockSet) InsertWithoutMerging(gap LockGapIterator, r LockRange, val Loc
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *LockSet) InsertWithoutMergingUnchecked(gap LockGapIterator, r LockRange, val Lock) LockIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := LocktrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return LockIterator{gap.node, gap.index}
 }
 
@@ -328,12 +369,20 @@ func (s *LockSet) Remove(seg LockIterator) LockGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if LocktrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	lockSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if LocktrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(LockGapIterator{seg.node, seg.index})
 }
 
@@ -383,6 +432,7 @@ func (s *LockSet) MergeUnchecked(first, second LockIterator) LockIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -558,6 +608,12 @@ type Locknode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap LockdynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [LockmaxDegree - 1]LockRange
@@ -603,12 +659,12 @@ func (n *Locknode) nextSibling() *Locknode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *Locknode) rebalanceBeforeInsert(gap LockGapIterator) LockGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < LockmaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &Locknode{
@@ -644,6 +700,11 @@ func (n *Locknode) rebalanceBeforeInsert(gap LockGapIterator) LockGapIterator {
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if LocktrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -681,6 +742,11 @@ func (n *Locknode) rebalanceBeforeInsert(gap LockGapIterator) LockGapIterator {
 	}
 	n.nrSegments = LockminDegree - 1
 
+	if LocktrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -726,6 +792,11 @@ func (n *Locknode) rebalanceAfterRemove(gap LockGapIterator) LockGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if LocktrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return LockGapIterator{n, 0}
 			}
@@ -754,6 +825,11 @@ func (n *Locknode) rebalanceAfterRemove(gap LockGapIterator) LockGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if LocktrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return LockGapIterator{n, n.nrSegments}
@@ -786,6 +862,7 @@ func (n *Locknode) rebalanceAfterRemove(gap LockGapIterator) LockGapIterator {
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return LockGapIterator{p, gap.index}
 			}
@@ -832,10 +909,146 @@ func (n *Locknode) rebalanceAfterRemove(gap LockGapIterator) LockGapIterator {
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if LocktrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *Locknode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *Locknode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *Locknode) calculateMaxGapLeaf() uint64 {
+	max := LockGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (LockGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *Locknode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *Locknode) searchFirstLargeEnoughGap(minSize uint64) LockGapIterator {
+	if n.maxGap.Get() < minSize {
+		return LockGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := LockGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *Locknode) searchLastLargeEnoughGap(minSize uint64) LockGapIterator {
+	if n.maxGap.Get() < minSize {
+		return LockGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := LockGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1141,6 +1354,114 @@ func (gap LockGapIterator) NextGap() LockGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap LockGapIterator) NextLargeEnoughGap(minSize uint64) LockGapIterator {
+	if LocktrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap LockGapIterator) nextLargeEnoughGapHelper(minSize uint64) LockGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return LockGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap LockGapIterator) PrevLargeEnoughGap(minSize uint64) LockGapIterator {
+	if LocktrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap LockGapIterator) prevLargeEnoughGapHelper(minSize uint64) LockGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return LockGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1207,7 +1528,15 @@ func (n *Locknode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if LocktrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1259,6 +1588,46 @@ func (s *LockSet) ImportSortedSlices(sds *LockSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *LockSet) segmentTestCheck(expectedSegments int, segFunc func(int, LockRange, Lock) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *LockSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *LockSet) saveRoot() *LockSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/fs/lock/lock_state_autogen.go b/pkg/sentry/fs/lock/lock_state_autogen.go
index a5db62814..d5ea98366 100755..100644
--- a/pkg/sentry/fs/lock/lock_state_autogen.go
+++ b/pkg/sentry/fs/lock/lock_state_autogen.go
@@ -67,6 +67,7 @@ func (x *Locknode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -78,6 +79,7 @@ func (x *Locknode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
diff --git a/pkg/sentry/fs/proc/device/device_state_autogen.go b/pkg/sentry/fs/proc/device/device_state_autogen.go
index 4a5e3cc88..4a5e3cc88 100755..100644
--- a/pkg/sentry/fs/proc/device/device_state_autogen.go
+++ b/pkg/sentry/fs/proc/device/device_state_autogen.go
diff --git a/pkg/sentry/fs/proc/proc_state_autogen.go b/pkg/sentry/fs/proc/proc_state_autogen.go
index baf7cd42b..baf7cd42b 100755..100644
--- a/pkg/sentry/fs/proc/proc_state_autogen.go
+++ b/pkg/sentry/fs/proc/proc_state_autogen.go
diff --git a/pkg/sentry/fs/proc/seqfile/seqfile_state_autogen.go b/pkg/sentry/fs/proc/seqfile/seqfile_state_autogen.go
index cfd3a40b4..cfd3a40b4 100755..100644
--- a/pkg/sentry/fs/proc/seqfile/seqfile_state_autogen.go
+++ b/pkg/sentry/fs/proc/seqfile/seqfile_state_autogen.go
diff --git a/pkg/sentry/fs/ramfs/ramfs_state_autogen.go b/pkg/sentry/fs/ramfs/ramfs_state_autogen.go
index 0a001e0b6..0a001e0b6 100755..100644
--- a/pkg/sentry/fs/ramfs/ramfs_state_autogen.go
+++ b/pkg/sentry/fs/ramfs/ramfs_state_autogen.go
diff --git a/pkg/sentry/fs/sys/sys_state_autogen.go b/pkg/sentry/fs/sys/sys_state_autogen.go
index 733c504b1..733c504b1 100755..100644
--- a/pkg/sentry/fs/sys/sys_state_autogen.go
+++ b/pkg/sentry/fs/sys/sys_state_autogen.go
diff --git a/pkg/sentry/fs/timerfd/timerfd_state_autogen.go b/pkg/sentry/fs/timerfd/timerfd_state_autogen.go
index 955cf1d38..955cf1d38 100755..100644
--- a/pkg/sentry/fs/timerfd/timerfd_state_autogen.go
+++ b/pkg/sentry/fs/timerfd/timerfd_state_autogen.go
diff --git a/pkg/sentry/fs/tmpfs/tmpfs_state_autogen.go b/pkg/sentry/fs/tmpfs/tmpfs_state_autogen.go
index e4d2584fd..e4d2584fd 100755..100644
--- a/pkg/sentry/fs/tmpfs/tmpfs_state_autogen.go
+++ b/pkg/sentry/fs/tmpfs/tmpfs_state_autogen.go
diff --git a/pkg/sentry/fs/tty/tty_state_autogen.go b/pkg/sentry/fs/tty/tty_state_autogen.go
index 25d601072..25d601072 100755..100644
--- a/pkg/sentry/fs/tty/tty_state_autogen.go
+++ b/pkg/sentry/fs/tty/tty_state_autogen.go
diff --git a/pkg/sentry/fs/user/user.go b/pkg/sentry/fs/user/user.go
index fe7f67c00..fe7f67c00 100755..100644
--- a/pkg/sentry/fs/user/user.go
+++ b/pkg/sentry/fs/user/user.go
diff --git a/pkg/sentry/fs/user/user_state_autogen.go b/pkg/sentry/fs/user/user_state_autogen.go
index 8083e036c..8083e036c 100755..100644
--- a/pkg/sentry/fs/user/user_state_autogen.go
+++ b/pkg/sentry/fs/user/user_state_autogen.go
diff --git a/pkg/sentry/fsbridge/bridge.go b/pkg/sentry/fsbridge/bridge.go
index 8e7590721..8e7590721 100755..100644
--- a/pkg/sentry/fsbridge/bridge.go
+++ b/pkg/sentry/fsbridge/bridge.go
diff --git a/pkg/sentry/fsbridge/fs.go b/pkg/sentry/fsbridge/fs.go
index 093ce1fb3..093ce1fb3 100755..100644
--- a/pkg/sentry/fsbridge/fs.go
+++ b/pkg/sentry/fsbridge/fs.go
diff --git a/pkg/sentry/fsbridge/fsbridge_state_autogen.go b/pkg/sentry/fsbridge/fsbridge_state_autogen.go
index d370b2d47..d370b2d47 100755..100644
--- a/pkg/sentry/fsbridge/fsbridge_state_autogen.go
+++ b/pkg/sentry/fsbridge/fsbridge_state_autogen.go
diff --git a/pkg/sentry/fsbridge/vfs.go b/pkg/sentry/fsbridge/vfs.go
index 89168220a..89168220a 100755..100644
--- a/pkg/sentry/fsbridge/vfs.go
+++ b/pkg/sentry/fsbridge/vfs.go
diff --git a/pkg/sentry/fsimpl/devpts/devpts.go b/pkg/sentry/fsimpl/devpts/devpts.go
index c03c65445..c03c65445 100755..100644
--- a/pkg/sentry/fsimpl/devpts/devpts.go
+++ b/pkg/sentry/fsimpl/devpts/devpts.go
diff --git a/pkg/sentry/fsimpl/devpts/devpts_state_autogen.go b/pkg/sentry/fsimpl/devpts/devpts_state_autogen.go
index 90cd7937c..90cd7937c 100755..100644
--- a/pkg/sentry/fsimpl/devpts/devpts_state_autogen.go
+++ b/pkg/sentry/fsimpl/devpts/devpts_state_autogen.go
diff --git a/pkg/sentry/fsimpl/devpts/line_discipline.go b/pkg/sentry/fsimpl/devpts/line_discipline.go
index f7bc325d1..f7bc325d1 100755..100644
--- a/pkg/sentry/fsimpl/devpts/line_discipline.go
+++ b/pkg/sentry/fsimpl/devpts/line_discipline.go
diff --git a/pkg/sentry/fsimpl/devpts/master.go b/pkg/sentry/fsimpl/devpts/master.go
index 7a7ce5d81..7a7ce5d81 100755..100644
--- a/pkg/sentry/fsimpl/devpts/master.go
+++ b/pkg/sentry/fsimpl/devpts/master.go
diff --git a/pkg/sentry/fsimpl/devpts/queue.go b/pkg/sentry/fsimpl/devpts/queue.go
index dffb4232c..dffb4232c 100755..100644
--- a/pkg/sentry/fsimpl/devpts/queue.go
+++ b/pkg/sentry/fsimpl/devpts/queue.go
diff --git a/pkg/sentry/fsimpl/devpts/slave.go b/pkg/sentry/fsimpl/devpts/slave.go
index 526cd406c..526cd406c 100755..100644
--- a/pkg/sentry/fsimpl/devpts/slave.go
+++ b/pkg/sentry/fsimpl/devpts/slave.go
diff --git a/pkg/sentry/fsimpl/devpts/terminal.go b/pkg/sentry/fsimpl/devpts/terminal.go
index 7d2781c54..7d2781c54 100755..100644
--- a/pkg/sentry/fsimpl/devpts/terminal.go
+++ b/pkg/sentry/fsimpl/devpts/terminal.go
diff --git a/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go b/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
index 142ee53b0..142ee53b0 100755..100644
--- a/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
+++ b/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
diff --git a/pkg/sentry/fsimpl/devtmpfs/devtmpfs_state_autogen.go b/pkg/sentry/fsimpl/devtmpfs/devtmpfs_state_autogen.go
index ac054eb77..ac054eb77 100755..100644
--- a/pkg/sentry/fsimpl/devtmpfs/devtmpfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/devtmpfs/devtmpfs_state_autogen.go
diff --git a/pkg/sentry/fsimpl/eventfd/eventfd.go b/pkg/sentry/fsimpl/eventfd/eventfd.go
index c573d7935..c573d7935 100755..100644
--- a/pkg/sentry/fsimpl/eventfd/eventfd.go
+++ b/pkg/sentry/fsimpl/eventfd/eventfd.go
diff --git a/pkg/sentry/fsimpl/eventfd/eventfd_state_autogen.go b/pkg/sentry/fsimpl/eventfd/eventfd_state_autogen.go
index e83f6aed8..e83f6aed8 100755..100644
--- a/pkg/sentry/fsimpl/eventfd/eventfd_state_autogen.go
+++ b/pkg/sentry/fsimpl/eventfd/eventfd_state_autogen.go
diff --git a/pkg/sentry/fsimpl/gofer/dentry_list.go b/pkg/sentry/fsimpl/gofer/dentry_list.go
index fa03e2501..fa03e2501 100755..100644
--- a/pkg/sentry/fsimpl/gofer/dentry_list.go
+++ b/pkg/sentry/fsimpl/gofer/dentry_list.go
diff --git a/pkg/sentry/fsimpl/gofer/directory.go b/pkg/sentry/fsimpl/gofer/directory.go
index b98218753..b98218753 100755..100644
--- a/pkg/sentry/fsimpl/gofer/directory.go
+++ b/pkg/sentry/fsimpl/gofer/directory.go
diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 7f2181216..7f2181216 100755..100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
diff --git a/pkg/sentry/fsimpl/gofer/fstree.go b/pkg/sentry/fsimpl/gofer/fstree.go
index 9ef0dd8c8..9ef0dd8c8 100755..100644
--- a/pkg/sentry/fsimpl/gofer/fstree.go
+++ b/pkg/sentry/fsimpl/gofer/fstree.go
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index ebf063a58..131da332f 100755..100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -84,12 +84,6 @@ type filesystem struct {
 	// devMinor is the filesystem's minor device number. devMinor is immutable.
 	devMinor uint32
 
-	// uid and gid are the effective KUID and KGID of the filesystem's creator,
-	// and are used as the owner and group for files that don't specify one.
-	// uid and gid are immutable.
-	uid auth.KUID
-	gid auth.KGID
-
 	// renameMu serves two purposes:
 	//
 	// - It synchronizes path resolution with renaming initiated by this
@@ -122,6 +116,8 @@ type filesystemOptions struct {
 	fd      int
 	aname   string
 	interop InteropMode // derived from the "cache" mount option
+	dfltuid auth.KUID
+	dfltgid auth.KGID
 	msize   uint32
 	version string
 
@@ -230,6 +226,15 @@ type InternalFilesystemOptions struct {
 	OpenSocketsByConnecting bool
 }
 
+// _V9FS_DEFUID and _V9FS_DEFGID (from Linux's fs/9p/v9fs.h) are the default
+// UIDs and GIDs used for files that do not provide a specific owner or group
+// respectively.
+const (
+	// uint32(-2) doesn't work in Go.
+	_V9FS_DEFUID = auth.KUID(4294967294)
+	_V9FS_DEFGID = auth.KGID(4294967294)
+)
+
 // Name implements vfs.FilesystemType.Name.
 func (FilesystemType) Name() string {
 	return Name
@@ -315,6 +320,31 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		}
 	}
 
+	// Parse the default UID and GID.
+	fsopts.dfltuid = _V9FS_DEFUID
+	if dfltuidstr, ok := mopts["dfltuid"]; ok {
+		delete(mopts, "dfltuid")
+		dfltuid, err := strconv.ParseUint(dfltuidstr, 10, 32)
+		if err != nil {
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid default UID: dfltuid=%s", dfltuidstr)
+			return nil, nil, syserror.EINVAL
+		}
+		// In Linux, dfltuid is interpreted as a UID and is converted to a KUID
+		// in the caller's user namespace, but goferfs isn't
+		// application-mountable.
+		fsopts.dfltuid = auth.KUID(dfltuid)
+	}
+	fsopts.dfltgid = _V9FS_DEFGID
+	if dfltgidstr, ok := mopts["dfltgid"]; ok {
+		delete(mopts, "dfltgid")
+		dfltgid, err := strconv.ParseUint(dfltgidstr, 10, 32)
+		if err != nil {
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid default UID: dfltgid=%s", dfltgidstr)
+			return nil, nil, syserror.EINVAL
+		}
+		fsopts.dfltgid = auth.KGID(dfltgid)
+	}
+
 	// Parse the 9P message size.
 	fsopts.msize = 1024 * 1024 // 1M, tested to give good enough performance up to 64M
 	if msizestr, ok := mopts["msize"]; ok {
@@ -422,8 +452,6 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		client:           client,
 		clock:            ktime.RealtimeClockFromContext(ctx),
 		devMinor:         devMinor,
-		uid:              creds.EffectiveKUID,
-		gid:              creds.EffectiveKGID,
 		syncableDentries: make(map[*dentry]struct{}),
 		specialFileFDs:   make(map[*specialFileFD]struct{}),
 	}
@@ -672,8 +700,8 @@ func (fs *filesystem) newDentry(ctx context.Context, file p9file, qid p9.QID, ma
 		file:      file,
 		ino:       qid.Path,
 		mode:      uint32(attr.Mode),
-		uid:       uint32(fs.uid),
-		gid:       uint32(fs.gid),
+		uid:       uint32(fs.opts.dfltuid),
+		gid:       uint32(fs.opts.dfltgid),
 		blockSize: usermem.PageSize,
 		handle: handle{
 			fd: -1,
@@ -928,8 +956,8 @@ func (d *dentry) setStat(ctx context.Context, creds *auth.Credentials, stat *lin
 		// so we can't race with Write or another truncate.)
 		d.dataMu.Unlock()
 		if d.size < oldSize {
-			oldpgend := pageRoundUp(oldSize)
-			newpgend := pageRoundUp(d.size)
+			oldpgend, _ := usermem.PageRoundUp(oldSize)
+			newpgend, _ := usermem.PageRoundUp(d.size)
 			if oldpgend != newpgend {
 				d.mapsMu.Lock()
 				d.mappings.Invalidate(memmap.MappableRange{newpgend, oldpgend}, memmap.InvalidateOpts{
diff --git a/pkg/sentry/fsimpl/gofer/gofer_state_autogen.go b/pkg/sentry/fsimpl/gofer/gofer_state_autogen.go
index 546d432c9..546d432c9 100755..100644
--- a/pkg/sentry/fsimpl/gofer/gofer_state_autogen.go
+++ b/pkg/sentry/fsimpl/gofer/gofer_state_autogen.go
diff --git a/pkg/sentry/fsimpl/gofer/handle.go b/pkg/sentry/fsimpl/gofer/handle.go
index 724a3f1f7..724a3f1f7 100755..100644
--- a/pkg/sentry/fsimpl/gofer/handle.go
+++ b/pkg/sentry/fsimpl/gofer/handle.go
diff --git a/pkg/sentry/fsimpl/gofer/p9file.go b/pkg/sentry/fsimpl/gofer/p9file.go
index 87f0b877f..87f0b877f 100755..100644
--- a/pkg/sentry/fsimpl/gofer/p9file.go
+++ b/pkg/sentry/fsimpl/gofer/p9file.go
diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index 857f7c74e..0d10cf7ac 100755..100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -148,9 +148,9 @@ func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, off
 			return 0, err
 		}
 		// Remove touched pages from the cache.
-		pgstart := pageRoundDown(uint64(offset))
-		pgend := pageRoundUp(uint64(offset + src.NumBytes()))
-		if pgend < pgstart {
+		pgstart := usermem.PageRoundDown(uint64(offset))
+		pgend, ok := usermem.PageRoundUp(uint64(offset + src.NumBytes()))
+		if !ok {
 			return 0, syserror.EINVAL
 		}
 		mr := memmap.MappableRange{pgstart, pgend}
@@ -306,9 +306,10 @@ func (rw *dentryReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error)
 			if fillCache {
 				// Read into the cache, then re-enter the loop to read from the
 				// cache.
+				gapEnd, _ := usermem.PageRoundUp(gapMR.End)
 				reqMR := memmap.MappableRange{
-					Start: pageRoundDown(gapMR.Start),
-					End:   pageRoundUp(gapMR.End),
+					Start: usermem.PageRoundDown(gapMR.Start),
+					End:   gapEnd,
 				}
 				optMR := gap.Range()
 				err := rw.d.cache.Fill(rw.ctx, reqMR, maxFillRange(reqMR, optMR), mf, usage.PageCache, rw.d.handle.readToBlocksAt)
@@ -671,7 +672,7 @@ func (d *dentry) Translate(ctx context.Context, required, optional memmap.Mappab
 
 	// Constrain translations to d.size (rounded up) to prevent translation to
 	// pages that may be concurrently truncated.
-	pgend := pageRoundUp(d.size)
+	pgend, _ := usermem.PageRoundUp(d.size)
 	var beyondEOF bool
 	if required.End > pgend {
 		if required.Start >= pgend {
@@ -818,43 +819,15 @@ type dentryPlatformFile struct {
 // IncRef implements platform.File.IncRef.
 func (d *dentryPlatformFile) IncRef(fr platform.FileRange) {
 	d.dataMu.Lock()
-	seg, gap := d.fdRefs.Find(fr.Start)
-	for {
-		switch {
-		case seg.Ok() && seg.Start() < fr.End:
-			seg = d.fdRefs.Isolate(seg, fr)
-			seg.SetValue(seg.Value() + 1)
-			seg, gap = seg.NextNonEmpty()
-		case gap.Ok() && gap.Start() < fr.End:
-			newRange := gap.Range().Intersect(fr)
-			usage.MemoryAccounting.Inc(newRange.Length(), usage.Mapped)
-			seg, gap = d.fdRefs.InsertWithoutMerging(gap, newRange, 1).NextNonEmpty()
-		default:
-			d.fdRefs.MergeAdjacent(fr)
-			d.dataMu.Unlock()
-			return
-		}
-	}
+	d.fdRefs.IncRefAndAccount(fr)
+	d.dataMu.Unlock()
 }
 
 // DecRef implements platform.File.DecRef.
 func (d *dentryPlatformFile) DecRef(fr platform.FileRange) {
 	d.dataMu.Lock()
-	seg := d.fdRefs.FindSegment(fr.Start)
-
-	for seg.Ok() && seg.Start() < fr.End {
-		seg = d.fdRefs.Isolate(seg, fr)
-		if old := seg.Value(); old == 1 {
-			usage.MemoryAccounting.Dec(seg.Range().Length(), usage.Mapped)
-			seg = d.fdRefs.Remove(seg).NextSegment()
-		} else {
-			seg.SetValue(old - 1)
-			seg = seg.NextSegment()
-		}
-	}
-	d.fdRefs.MergeAdjacent(fr)
+	d.fdRefs.DecRefAndAccount(fr)
 	d.dataMu.Unlock()
-
 }
 
 // MapInternal implements platform.File.MapInternal.
diff --git a/pkg/sentry/fsimpl/gofer/socket.go b/pkg/sentry/fsimpl/gofer/socket.go
index d6dbe9092..d6dbe9092 100755..100644
--- a/pkg/sentry/fsimpl/gofer/socket.go
+++ b/pkg/sentry/fsimpl/gofer/socket.go
diff --git a/pkg/sentry/fsimpl/gofer/special_file.go b/pkg/sentry/fsimpl/gofer/special_file.go
index a464e6a94..a464e6a94 100755..100644
--- a/pkg/sentry/fsimpl/gofer/special_file.go
+++ b/pkg/sentry/fsimpl/gofer/special_file.go
diff --git a/pkg/sentry/fsimpl/gofer/symlink.go b/pkg/sentry/fsimpl/gofer/symlink.go
index 2ec819f86..2ec819f86 100755..100644
--- a/pkg/sentry/fsimpl/gofer/symlink.go
+++ b/pkg/sentry/fsimpl/gofer/symlink.go
diff --git a/pkg/sentry/fsimpl/gofer/time.go b/pkg/sentry/fsimpl/gofer/time.go
index 2608e7e1d..2608e7e1d 100755..100644
--- a/pkg/sentry/fsimpl/gofer/time.go
+++ b/pkg/sentry/fsimpl/gofer/time.go
diff --git a/pkg/sentry/fsimpl/host/control.go b/pkg/sentry/fsimpl/host/control.go
index b9082a20f..b9082a20f 100755..100644
--- a/pkg/sentry/fsimpl/host/control.go
+++ b/pkg/sentry/fsimpl/host/control.go
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index 8caf55a1b..18b127521 100755..100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -86,15 +86,13 @@ func NewFD(ctx context.Context, mnt *vfs.Mount, hostFD int, opts *NewFDOptions)
 
 	i := &inode{
 		hostFD:     hostFD,
-		seekable:   seekable,
+		ino:        fs.NextIno(),
 		isTTY:      opts.IsTTY,
-		canMap:     canMap(uint32(fileType)),
 		wouldBlock: wouldBlock(uint32(fileType)),
-		ino:        fs.NextIno(),
-		// For simplicity, set offset to 0. Technically, we should use the existing
-		// offset on the host if the file is seekable.
-		offset: 0,
+		seekable:   seekable,
+		canMap:     canMap(uint32(fileType)),
 	}
+	i.pf.inode = i
 
 	// Non-seekable files can't be memory mapped, assert this.
 	if !i.seekable && i.canMap {
@@ -117,6 +115,10 @@ func NewFD(ctx context.Context, mnt *vfs.Mount, hostFD int, opts *NewFDOptions)
 
 	// i.open will take a reference on d.
 	defer d.DecRef()
+
+	// For simplicity, fileDescription.offset is set to 0. Technically, we
+	// should only set to 0 on files that are not seekable (sockets, pipes,
+	// etc.), and use the offset from the host fd otherwise when importing.
 	return i.open(ctx, d.VFSDentry(), mnt, flags)
 }
 
@@ -189,11 +191,15 @@ type inode struct {
 	// This field is initialized at creation time and is immutable.
 	hostFD int
 
-	// wouldBlock is true if the host FD would return EWOULDBLOCK for
-	// operations that would block.
+	// ino is an inode number unique within this filesystem.
 	//
 	// This field is initialized at creation time and is immutable.
-	wouldBlock bool
+	ino uint64
+
+	// isTTY is true if this file represents a TTY.
+	//
+	// This field is initialized at creation time and is immutable.
+	isTTY bool
 
 	// seekable is false if the host fd points to a file representing a stream,
 	// e.g. a socket or a pipe. Such files are not seekable and can return
@@ -202,29 +208,29 @@ type inode struct {
 	// This field is initialized at creation time and is immutable.
 	seekable bool
 
-	// isTTY is true if this file represents a TTY.
+	// wouldBlock is true if the host FD would return EWOULDBLOCK for
+	// operations that would block.
 	//
 	// This field is initialized at creation time and is immutable.
-	isTTY bool
+	wouldBlock bool
+
+	// Event queue for blocking operations.
+	queue waiter.Queue
 
 	// canMap specifies whether we allow the file to be memory mapped.
 	//
 	// This field is initialized at creation time and is immutable.
 	canMap bool
 
-	// ino is an inode number unique within this filesystem.
-	//
-	// This field is initialized at creation time and is immutable.
-	ino uint64
+	// mapsMu protects mappings.
+	mapsMu sync.Mutex
 
-	// offsetMu protects offset.
-	offsetMu sync.Mutex
-
-	// offset specifies the current file offset.
-	offset int64
+	// If canMap is true, mappings tracks mappings of hostFD into
+	// memmap.MappingSpaces.
+	mappings memmap.MappingSet
 
-	// Event queue for blocking operations.
-	queue waiter.Queue
+	// pf implements platform.File for mappings of hostFD.
+	pf inodePlatformFile
 }
 
 // CheckPermissions implements kernfs.Inode.
@@ -388,6 +394,21 @@ func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Cre
 		if err := syscall.Ftruncate(i.hostFD, int64(s.Size)); err != nil {
 			return err
 		}
+		oldSize := uint64(hostStat.Size)
+		if s.Size < oldSize {
+			oldpgend, _ := usermem.PageRoundUp(oldSize)
+			newpgend, _ := usermem.PageRoundUp(s.Size)
+			if oldpgend != newpgend {
+				i.mapsMu.Lock()
+				i.mappings.Invalidate(memmap.MappableRange{newpgend, oldpgend}, memmap.InvalidateOpts{
+					// Compare Linux's mm/truncate.c:truncate_setsize() =>
+					// truncate_pagecache() =>
+					// mm/memory.c:unmap_mapping_range(evencows=1).
+					InvalidatePrivate: true,
+				})
+				i.mapsMu.Unlock()
+			}
+		}
 	}
 	if m&(linux.STATX_ATIME|linux.STATX_MTIME) != 0 {
 		ts := [2]syscall.Timespec{
@@ -464,9 +485,6 @@ func (i *inode) open(ctx context.Context, d *vfs.Dentry, mnt *vfs.Mount, flags u
 		return vfsfd, nil
 	}
 
-	// For simplicity, set offset to 0. Technically, we should
-	// only set to 0 on files that are not seekable (sockets, pipes, etc.),
-	// and use the offset from the host fd otherwise.
 	fd := &fileDescription{inode: i}
 	vfsfd := &fd.vfsfd
 	if err := vfsfd.Init(fd, flags, mnt, d, &vfs.FileDescriptionOptions{}); err != nil {
@@ -487,6 +505,13 @@ type fileDescription struct {
 	//
 	// inode is immutable after fileDescription creation.
 	inode *inode
+
+	// offsetMu protects offset.
+	offsetMu sync.Mutex
+
+	// offset specifies the current file offset. It is only meaningful when
+	// inode.seekable is true.
+	offset int64
 }
 
 // SetStat implements vfs.FileDescriptionImpl.
@@ -532,10 +557,10 @@ func (f *fileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts
 		return n, err
 	}
 	// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
-	i.offsetMu.Lock()
-	n, err := readFromHostFD(ctx, i.hostFD, dst, i.offset, opts.Flags)
-	i.offset += n
-	i.offsetMu.Unlock()
+	f.offsetMu.Lock()
+	n, err := readFromHostFD(ctx, i.hostFD, dst, f.offset, opts.Flags)
+	f.offset += n
+	f.offsetMu.Unlock()
 	return n, err
 }
 
@@ -572,10 +597,10 @@ func (f *fileDescription) Write(ctx context.Context, src usermem.IOSequence, opt
 	}
 	// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
 	// TODO(gvisor.dev/issue/1672): Write to end of file and update offset if O_APPEND is set on this file.
-	i.offsetMu.Lock()
-	n, err := writeToHostFD(ctx, i.hostFD, src, i.offset, opts.Flags)
-	i.offset += n
-	i.offsetMu.Unlock()
+	f.offsetMu.Lock()
+	n, err := writeToHostFD(ctx, i.hostFD, src, f.offset, opts.Flags)
+	f.offset += n
+	f.offsetMu.Unlock()
 	return n, err
 }
 
@@ -600,41 +625,41 @@ func (f *fileDescription) Seek(_ context.Context, offset int64, whence int32) (i
 		return 0, syserror.ESPIPE
 	}
 
-	i.offsetMu.Lock()
-	defer i.offsetMu.Unlock()
+	f.offsetMu.Lock()
+	defer f.offsetMu.Unlock()
 
 	switch whence {
 	case linux.SEEK_SET:
 		if offset < 0 {
-			return i.offset, syserror.EINVAL
+			return f.offset, syserror.EINVAL
 		}
-		i.offset = offset
+		f.offset = offset
 
 	case linux.SEEK_CUR:
-		// Check for overflow. Note that underflow cannot occur, since i.offset >= 0.
-		if offset > math.MaxInt64-i.offset {
-			return i.offset, syserror.EOVERFLOW
+		// Check for overflow. Note that underflow cannot occur, since f.offset >= 0.
+		if offset > math.MaxInt64-f.offset {
+			return f.offset, syserror.EOVERFLOW
 		}
-		if i.offset+offset < 0 {
-			return i.offset, syserror.EINVAL
+		if f.offset+offset < 0 {
+			return f.offset, syserror.EINVAL
 		}
-		i.offset += offset
+		f.offset += offset
 
 	case linux.SEEK_END:
 		var s syscall.Stat_t
 		if err := syscall.Fstat(i.hostFD, &s); err != nil {
-			return i.offset, err
+			return f.offset, err
 		}
 		size := s.Size
 
 		// Check for overflow. Note that underflow cannot occur, since size >= 0.
 		if offset > math.MaxInt64-size {
-			return i.offset, syserror.EOVERFLOW
+			return f.offset, syserror.EOVERFLOW
 		}
 		if size+offset < 0 {
-			return i.offset, syserror.EINVAL
+			return f.offset, syserror.EINVAL
 		}
-		i.offset = size + offset
+		f.offset = size + offset
 
 	case linux.SEEK_DATA, linux.SEEK_HOLE:
 		// Modifying the offset in the host file table should not matter, since
@@ -643,16 +668,16 @@ func (f *fileDescription) Seek(_ context.Context, offset int64, whence int32) (i
 		// For reading and writing, we always rely on our internal offset.
 		n, err := unix.Seek(i.hostFD, offset, int(whence))
 		if err != nil {
-			return i.offset, err
+			return f.offset, err
 		}
-		i.offset = n
+		f.offset = n
 
 	default:
 		// Invalid whence.
-		return i.offset, syserror.EINVAL
+		return f.offset, syserror.EINVAL
 	}
 
-	return i.offset, nil
+	return f.offset, nil
 }
 
 // Sync implements FileDescriptionImpl.
@@ -666,8 +691,9 @@ func (f *fileDescription) ConfigureMMap(_ context.Context, opts *memmap.MMapOpts
 	if !f.inode.canMap {
 		return syserror.ENODEV
 	}
-	// TODO(gvisor.dev/issue/1672): Implement ConfigureMMap and Mappable interface.
-	return syserror.ENODEV
+	i := f.inode
+	i.pf.fileMapperInitOnce.Do(i.pf.fileMapper.Init)
+	return vfs.GenericConfigureMMap(&f.vfsfd, i, opts)
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
diff --git a/pkg/sentry/fsimpl/host/host_state_autogen.go b/pkg/sentry/fsimpl/host/host_state_autogen.go
index 28bc79d04..28bc79d04 100755..100644
--- a/pkg/sentry/fsimpl/host/host_state_autogen.go
+++ b/pkg/sentry/fsimpl/host/host_state_autogen.go
diff --git a/pkg/sentry/fsimpl/host/host_unsafe_state_autogen.go b/pkg/sentry/fsimpl/host/host_unsafe_state_autogen.go
index b2d8c661f..b2d8c661f 100755..100644
--- a/pkg/sentry/fsimpl/host/host_unsafe_state_autogen.go
+++ b/pkg/sentry/fsimpl/host/host_unsafe_state_autogen.go
diff --git a/pkg/sentry/fsimpl/host/ioctl_unsafe.go b/pkg/sentry/fsimpl/host/ioctl_unsafe.go
index 0983bf7d8..0983bf7d8 100755..100644
--- a/pkg/sentry/fsimpl/host/ioctl_unsafe.go
+++ b/pkg/sentry/fsimpl/host/ioctl_unsafe.go
diff --git a/pkg/sentry/fsimpl/host/mmap.go b/pkg/sentry/fsimpl/host/mmap.go
new file mode 100644
index 000000000..8545a82f0
--- /dev/null
+++ b/pkg/sentry/fsimpl/host/mmap.go
@@ -0,0 +1,132 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package host
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/platform"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// inodePlatformFile implements platform.File. It exists solely because inode
+// cannot implement both kernfs.Inode.IncRef and platform.File.IncRef.
+//
+// inodePlatformFile should only be used if inode.canMap is true.
+type inodePlatformFile struct {
+	*inode
+
+	// fdRefsMu protects fdRefs.
+	fdRefsMu sync.Mutex
+
+	// fdRefs counts references on platform.File offsets. It is used solely for
+	// memory accounting.
+	fdRefs fsutil.FrameRefSet
+
+	// fileMapper caches mappings of the host file represented by this inode.
+	fileMapper fsutil.HostFileMapper
+
+	// fileMapperInitOnce is used to lazily initialize fileMapper.
+	fileMapperInitOnce sync.Once
+}
+
+// IncRef implements platform.File.IncRef.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inodePlatformFile) IncRef(fr platform.FileRange) {
+	i.fdRefsMu.Lock()
+	i.fdRefs.IncRefAndAccount(fr)
+	i.fdRefsMu.Unlock()
+}
+
+// DecRef implements platform.File.DecRef.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inodePlatformFile) DecRef(fr platform.FileRange) {
+	i.fdRefsMu.Lock()
+	i.fdRefs.DecRefAndAccount(fr)
+	i.fdRefsMu.Unlock()
+}
+
+// MapInternal implements platform.File.MapInternal.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inodePlatformFile) MapInternal(fr platform.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
+	return i.fileMapper.MapInternal(fr, i.hostFD, at.Write)
+}
+
+// FD implements platform.File.FD.
+func (i *inodePlatformFile) FD() int {
+	return i.hostFD
+}
+
+// AddMapping implements memmap.Mappable.AddMapping.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inode) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
+	i.mapsMu.Lock()
+	mapped := i.mappings.AddMapping(ms, ar, offset, writable)
+	for _, r := range mapped {
+		i.pf.fileMapper.IncRefOn(r)
+	}
+	i.mapsMu.Unlock()
+	return nil
+}
+
+// RemoveMapping implements memmap.Mappable.RemoveMapping.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inode) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) {
+	i.mapsMu.Lock()
+	unmapped := i.mappings.RemoveMapping(ms, ar, offset, writable)
+	for _, r := range unmapped {
+		i.pf.fileMapper.DecRefOn(r)
+	}
+	i.mapsMu.Unlock()
+}
+
+// CopyMapping implements memmap.Mappable.CopyMapping.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inode) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, writable bool) error {
+	return i.AddMapping(ctx, ms, dstAR, offset, writable)
+}
+
+// Translate implements memmap.Mappable.Translate.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inode) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
+	mr := optional
+	return []memmap.Translation{
+		{
+			Source: mr,
+			File:   &i.pf,
+			Offset: mr.Start,
+			Perms:  usermem.AnyAccess,
+		},
+	}, nil
+}
+
+// InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
+//
+// Precondition: i.inode.canMap must be true.
+func (i *inode) InvalidateUnsavable(ctx context.Context) error {
+	// We expect the same host fd across save/restore, so all translations
+	// should be valid.
+	return nil
+}
diff --git a/pkg/sentry/fsimpl/host/socket.go b/pkg/sentry/fsimpl/host/socket.go
index 38f1fbfba..38f1fbfba 100755..100644
--- a/pkg/sentry/fsimpl/host/socket.go
+++ b/pkg/sentry/fsimpl/host/socket.go
diff --git a/pkg/sentry/fsimpl/host/socket_iovec.go b/pkg/sentry/fsimpl/host/socket_iovec.go
index 584c247d2..584c247d2 100755..100644
--- a/pkg/sentry/fsimpl/host/socket_iovec.go
+++ b/pkg/sentry/fsimpl/host/socket_iovec.go
diff --git a/pkg/sentry/fsimpl/host/socket_unsafe.go b/pkg/sentry/fsimpl/host/socket_unsafe.go
index 35ded24bc..35ded24bc 100755..100644
--- a/pkg/sentry/fsimpl/host/socket_unsafe.go
+++ b/pkg/sentry/fsimpl/host/socket_unsafe.go
diff --git a/pkg/sentry/fsimpl/host/tty.go b/pkg/sentry/fsimpl/host/tty.go
index 68af6e5af..68af6e5af 100755..100644
--- a/pkg/sentry/fsimpl/host/tty.go
+++ b/pkg/sentry/fsimpl/host/tty.go
diff --git a/pkg/sentry/fsimpl/host/util.go b/pkg/sentry/fsimpl/host/util.go
index 2bc757b1a..2bc757b1a 100755..100644
--- a/pkg/sentry/fsimpl/host/util.go
+++ b/pkg/sentry/fsimpl/host/util.go
diff --git a/pkg/sentry/fsimpl/host/util_unsafe.go b/pkg/sentry/fsimpl/host/util_unsafe.go
index 5136ac844..5136ac844 100755..100644
--- a/pkg/sentry/fsimpl/host/util_unsafe.go
+++ b/pkg/sentry/fsimpl/host/util_unsafe.go
diff --git a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
index 1568a9d49..1568a9d49 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
+++ b/pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go
diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
index 8284e76a7..8284e76a7 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 4a12ae245..4a12ae245 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
diff --git a/pkg/sentry/fsimpl/kernfs/fstree.go b/pkg/sentry/fsimpl/kernfs/fstree.go
index 4c4033462..4c4033462 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/fstree.go
+++ b/pkg/sentry/fsimpl/kernfs/fstree.go
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index 982daa2e6..982daa2e6 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index a83151ad3..a83151ad3 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go b/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
index 299ad87fa..299ad87fa 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_state_autogen.go
diff --git a/pkg/sentry/fsimpl/kernfs/slot_list.go b/pkg/sentry/fsimpl/kernfs/slot_list.go
index 09c30bca7..09c30bca7 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/slot_list.go
+++ b/pkg/sentry/fsimpl/kernfs/slot_list.go
diff --git a/pkg/sentry/fsimpl/kernfs/symlink.go b/pkg/sentry/fsimpl/kernfs/symlink.go
index 2ab3f53fd..2ab3f53fd 100755..100644
--- a/pkg/sentry/fsimpl/kernfs/symlink.go
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go
diff --git a/pkg/sentry/fsimpl/pipefs/pipefs.go b/pkg/sentry/fsimpl/pipefs/pipefs.go
index cab771211..cab771211 100755..100644
--- a/pkg/sentry/fsimpl/pipefs/pipefs.go
+++ b/pkg/sentry/fsimpl/pipefs/pipefs.go
diff --git a/pkg/sentry/fsimpl/pipefs/pipefs_state_autogen.go b/pkg/sentry/fsimpl/pipefs/pipefs_state_autogen.go
index e3e3887cd..e3e3887cd 100755..100644
--- a/pkg/sentry/fsimpl/pipefs/pipefs_state_autogen.go
+++ b/pkg/sentry/fsimpl/pipefs/pipefs_state_autogen.go
diff --git a/pkg/sentry/fsimpl/proc/filesystem.go b/pkg/sentry/fsimpl/proc/filesystem.go
index 609210253..609210253 100755..100644
--- a/pkg/sentry/fsimpl/proc/filesystem.go
+++ b/pkg/sentry/fsimpl/proc/filesystem.go
diff --git a/pkg/sentry/fsimpl/proc/proc_state_autogen.go b/pkg/sentry/fsimpl/proc/proc_state_autogen.go
index 168e61390..168e61390 100755..100644
--- a/pkg/sentry/fsimpl/proc/proc_state_autogen.go
+++ b/pkg/sentry/fsimpl/proc/proc_state_autogen.go
diff --git a/pkg/sentry/fsimpl/proc/subtasks.go b/pkg/sentry/fsimpl/proc/subtasks.go
index 36a911db4..36a911db4 100755..100644
--- a/pkg/sentry/fsimpl/proc/subtasks.go
+++ b/pkg/sentry/fsimpl/proc/subtasks.go
diff --git a/pkg/sentry/fsimpl/proc/task.go b/pkg/sentry/fsimpl/proc/task.go
index 482055db1..482055db1 100755..100644
--- a/pkg/sentry/fsimpl/proc/task.go
+++ b/pkg/sentry/fsimpl/proc/task.go
diff --git a/pkg/sentry/fsimpl/proc/task_fds.go b/pkg/sentry/fsimpl/proc/task_fds.go
index 44ccc9e4a..44ccc9e4a 100755..100644
--- a/pkg/sentry/fsimpl/proc/task_fds.go
+++ b/pkg/sentry/fsimpl/proc/task_fds.go
diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index 2f297e48a..2f297e48a 100755..100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
diff --git a/pkg/sentry/fsimpl/proc/task_net.go b/pkg/sentry/fsimpl/proc/task_net.go
index 6bde27376..6bde27376 100755..100644
--- a/pkg/sentry/fsimpl/proc/task_net.go
+++ b/pkg/sentry/fsimpl/proc/task_net.go
diff --git a/pkg/sentry/fsimpl/proc/tasks.go b/pkg/sentry/fsimpl/proc/tasks.go
index b51d43954..b51d43954 100755..100644
--- a/pkg/sentry/fsimpl/proc/tasks.go
+++ b/pkg/sentry/fsimpl/proc/tasks.go
diff --git a/pkg/sentry/fsimpl/proc/tasks_files.go b/pkg/sentry/fsimpl/proc/tasks_files.go
index 7d8983aa5..7d8983aa5 100755..100644
--- a/pkg/sentry/fsimpl/proc/tasks_files.go
+++ b/pkg/sentry/fsimpl/proc/tasks_files.go
diff --git a/pkg/sentry/fsimpl/proc/tasks_sys.go b/pkg/sentry/fsimpl/proc/tasks_sys.go
index 6dac2afa4..6dac2afa4 100755..100644
--- a/pkg/sentry/fsimpl/proc/tasks_sys.go
+++ b/pkg/sentry/fsimpl/proc/tasks_sys.go
diff --git a/pkg/sentry/fsimpl/signalfd/signalfd.go b/pkg/sentry/fsimpl/signalfd/signalfd.go
index d29ef3f83..d29ef3f83 100755..100644
--- a/pkg/sentry/fsimpl/signalfd/signalfd.go
+++ b/pkg/sentry/fsimpl/signalfd/signalfd.go
diff --git a/pkg/sentry/fsimpl/signalfd/signalfd_state_autogen.go b/pkg/sentry/fsimpl/signalfd/signalfd_state_autogen.go
index c3d9b2ffb..c3d9b2ffb 100755..100644
--- a/pkg/sentry/fsimpl/signalfd/signalfd_state_autogen.go
+++ b/pkg/sentry/fsimpl/signalfd/signalfd_state_autogen.go
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
index ee0828a15..ee0828a15 100755..100644
--- a/pkg/sentry/fsimpl/sockfs/sockfs.go
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go b/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go
index 8d5b85e2c..8d5b85e2c 100755..100644
--- a/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/sockfs/sockfs_state_autogen.go
diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index 0af373604..0af373604 100755..100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
diff --git a/pkg/sentry/fsimpl/sys/sys_state_autogen.go b/pkg/sentry/fsimpl/sys/sys_state_autogen.go
index 8866ddff9..8866ddff9 100755..100644
--- a/pkg/sentry/fsimpl/sys/sys_state_autogen.go
+++ b/pkg/sentry/fsimpl/sys/sys_state_autogen.go
diff --git a/pkg/sentry/fsimpl/timerfd/timerfd.go b/pkg/sentry/fsimpl/timerfd/timerfd.go
index 60c92d626..60c92d626 100755..100644
--- a/pkg/sentry/fsimpl/timerfd/timerfd.go
+++ b/pkg/sentry/fsimpl/timerfd/timerfd.go
diff --git a/pkg/sentry/fsimpl/timerfd/timerfd_state_autogen.go b/pkg/sentry/fsimpl/timerfd/timerfd_state_autogen.go
index 4e5976369..4e5976369 100755..100644
--- a/pkg/sentry/fsimpl/timerfd/timerfd_state_autogen.go
+++ b/pkg/sentry/fsimpl/timerfd/timerfd_state_autogen.go
diff --git a/pkg/sentry/fsimpl/tmpfs/dentry_list.go b/pkg/sentry/fsimpl/tmpfs/dentry_list.go
index 9af621dd3..9af621dd3 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/dentry_list.go
+++ b/pkg/sentry/fsimpl/tmpfs/dentry_list.go
diff --git a/pkg/sentry/fsimpl/tmpfs/device_file.go b/pkg/sentry/fsimpl/tmpfs/device_file.go
index 83bf885ee..83bf885ee 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/device_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/device_file.go
diff --git a/pkg/sentry/fsimpl/tmpfs/directory.go b/pkg/sentry/fsimpl/tmpfs/directory.go
index f2399981b..f2399981b 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/directory.go
+++ b/pkg/sentry/fsimpl/tmpfs/directory.go
diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index 80fa7b29d..80fa7b29d 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
diff --git a/pkg/sentry/fsimpl/tmpfs/fstree.go b/pkg/sentry/fsimpl/tmpfs/fstree.go
index fab366345..fab366345 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/fstree.go
+++ b/pkg/sentry/fsimpl/tmpfs/fstree.go
diff --git a/pkg/sentry/fsimpl/tmpfs/named_pipe.go b/pkg/sentry/fsimpl/tmpfs/named_pipe.go
index 8d77b3fa8..8d77b3fa8 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/named_pipe.go
+++ b/pkg/sentry/fsimpl/tmpfs/named_pipe.go
diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
index 3f433d666..fee174375 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/regular_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -312,7 +312,7 @@ func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, off
 	f := fd.inode().impl.(*regularFile)
 	if end := offset + srclen; end < offset {
 		// Overflow.
-		return 0, syserror.EFBIG
+		return 0, syserror.EINVAL
 	}
 
 	var err error
diff --git a/pkg/sentry/fsimpl/tmpfs/socket_file.go b/pkg/sentry/fsimpl/tmpfs/socket_file.go
index 25c2321af..25c2321af 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/socket_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/socket_file.go
diff --git a/pkg/sentry/fsimpl/tmpfs/symlink.go b/pkg/sentry/fsimpl/tmpfs/symlink.go
index 47e075ed4..47e075ed4 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/symlink.go
+++ b/pkg/sentry/fsimpl/tmpfs/symlink.go
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index 1e781aecd..1e781aecd 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go b/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
index 10d8b49a6..10d8b49a6 100755..100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
diff --git a/pkg/sentry/hostcpu/getcpu_arm64.s b/pkg/sentry/hostcpu/getcpu_arm64.s
index caf9abb89..caf9abb89 100755..100644
--- a/pkg/sentry/hostcpu/getcpu_arm64.s
+++ b/pkg/sentry/hostcpu/getcpu_arm64.s
diff --git a/pkg/sentry/hostcpu/hostcpu_state_autogen.go b/pkg/sentry/hostcpu/hostcpu_state_autogen.go
index 97d33d8bf..97d33d8bf 100755..100644
--- a/pkg/sentry/hostcpu/hostcpu_state_autogen.go
+++ b/pkg/sentry/hostcpu/hostcpu_state_autogen.go
diff --git a/pkg/sentry/hostfd/hostfd.go b/pkg/sentry/hostfd/hostfd.go
index 70dd9cafb..70dd9cafb 100755..100644
--- a/pkg/sentry/hostfd/hostfd.go
+++ b/pkg/sentry/hostfd/hostfd.go
diff --git a/pkg/sentry/hostfd/hostfd_state_autogen.go b/pkg/sentry/hostfd/hostfd_state_autogen.go
index 9033424d5..9033424d5 100755..100644
--- a/pkg/sentry/hostfd/hostfd_state_autogen.go
+++ b/pkg/sentry/hostfd/hostfd_state_autogen.go
diff --git a/pkg/sentry/hostfd/hostfd_unsafe.go b/pkg/sentry/hostfd/hostfd_unsafe.go
index cd4dc67fb..cd4dc67fb 100755..100644
--- a/pkg/sentry/hostfd/hostfd_unsafe.go
+++ b/pkg/sentry/hostfd/hostfd_unsafe.go
diff --git a/pkg/sentry/hostfd/hostfd_unsafe_state_autogen.go b/pkg/sentry/hostfd/hostfd_unsafe_state_autogen.go
index 9033424d5..9033424d5 100755..100644
--- a/pkg/sentry/hostfd/hostfd_unsafe_state_autogen.go
+++ b/pkg/sentry/hostfd/hostfd_unsafe_state_autogen.go
diff --git a/pkg/sentry/hostmm/hostmm_state_autogen.go b/pkg/sentry/hostmm/hostmm_state_autogen.go
index 925c56e14..925c56e14 100755..100644
--- a/pkg/sentry/hostmm/hostmm_state_autogen.go
+++ b/pkg/sentry/hostmm/hostmm_state_autogen.go
diff --git a/pkg/sentry/inet/inet_state_autogen.go b/pkg/sentry/inet/inet_state_autogen.go
index d2985113b..d2985113b 100755..100644
--- a/pkg/sentry/inet/inet_state_autogen.go
+++ b/pkg/sentry/inet/inet_state_autogen.go
diff --git a/pkg/sentry/inet/namespace.go b/pkg/sentry/inet/namespace.go
index 029af3025..029af3025 100755..100644
--- a/pkg/sentry/inet/namespace.go
+++ b/pkg/sentry/inet/namespace.go
diff --git a/pkg/sentry/kernel/auth/atomicptr_credentials_unsafe.go b/pkg/sentry/kernel/auth/atomicptr_credentials_unsafe.go
index 4535c958f..4535c958f 100755..100644
--- a/pkg/sentry/kernel/auth/atomicptr_credentials_unsafe.go
+++ b/pkg/sentry/kernel/auth/atomicptr_credentials_unsafe.go
diff --git a/pkg/sentry/kernel/auth/auth_state_autogen.go b/pkg/sentry/kernel/auth/auth_state_autogen.go
index 5b97d58a6..36e3576e8 100755..100644
--- a/pkg/sentry/kernel/auth/auth_state_autogen.go
+++ b/pkg/sentry/kernel/auth/auth_state_autogen.go
@@ -88,6 +88,7 @@ func (x *idMapnode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -99,6 +100,7 @@ func (x *idMapnode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
diff --git a/pkg/sentry/kernel/auth/auth_unsafe_state_autogen.go b/pkg/sentry/kernel/auth/auth_unsafe_state_autogen.go
index 6589b612c..6589b612c 100755..100644
--- a/pkg/sentry/kernel/auth/auth_unsafe_state_autogen.go
+++ b/pkg/sentry/kernel/auth/auth_unsafe_state_autogen.go
diff --git a/pkg/sentry/kernel/auth/id_map_range.go b/pkg/sentry/kernel/auth/id_map_range.go
index 833fa3518..833fa3518 100755..100644
--- a/pkg/sentry/kernel/auth/id_map_range.go
+++ b/pkg/sentry/kernel/auth/id_map_range.go
diff --git a/pkg/sentry/kernel/auth/id_map_set.go b/pkg/sentry/kernel/auth/id_map_set.go
index 73a17f281..983a036c5 100755..100644
--- a/pkg/sentry/kernel/auth/id_map_set.go
+++ b/pkg/sentry/kernel/auth/id_map_set.go
@@ -5,6 +5,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const idMaptrackGaps = 0
+
+var _ = uint8(idMaptrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type idMapdynamicGap [idMaptrackGaps]uint32
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *idMapdynamicGap) Get() uint32 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *idMapdynamicGap) Set(v uint32) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -263,8 +291,12 @@ func (s *idMapSet) Insert(gap idMapGapIterator, r idMapRange, val uint32) idMapI
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (idMapFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := idMaptrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (idMapFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -278,11 +310,16 @@ func (s *idMapSet) Insert(gap idMapGapIterator, r idMapRange, val uint32) idMapI
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (idMapFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := idMaptrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -309,11 +346,15 @@ func (s *idMapSet) InsertWithoutMerging(gap idMapGapIterator, r idMapRange, val
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *idMapSet) InsertWithoutMergingUnchecked(gap idMapGapIterator, r idMapRange, val uint32) idMapIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := idMaptrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return idMapIterator{gap.node, gap.index}
 }
 
@@ -328,12 +369,20 @@ func (s *idMapSet) Remove(seg idMapIterator) idMapGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if idMaptrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	idMapFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if idMaptrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(idMapGapIterator{seg.node, seg.index})
 }
 
@@ -383,6 +432,7 @@ func (s *idMapSet) MergeUnchecked(first, second idMapIterator) idMapIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -558,6 +608,12 @@ type idMapnode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap idMapdynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [idMapmaxDegree - 1]idMapRange
@@ -603,12 +659,12 @@ func (n *idMapnode) nextSibling() *idMapnode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *idMapnode) rebalanceBeforeInsert(gap idMapGapIterator) idMapGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < idMapmaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &idMapnode{
@@ -644,6 +700,11 @@ func (n *idMapnode) rebalanceBeforeInsert(gap idMapGapIterator) idMapGapIterator
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if idMaptrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -681,6 +742,11 @@ func (n *idMapnode) rebalanceBeforeInsert(gap idMapGapIterator) idMapGapIterator
 	}
 	n.nrSegments = idMapminDegree - 1
 
+	if idMaptrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -726,6 +792,11 @@ func (n *idMapnode) rebalanceAfterRemove(gap idMapGapIterator) idMapGapIterator
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if idMaptrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return idMapGapIterator{n, 0}
 			}
@@ -754,6 +825,11 @@ func (n *idMapnode) rebalanceAfterRemove(gap idMapGapIterator) idMapGapIterator
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if idMaptrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return idMapGapIterator{n, n.nrSegments}
@@ -786,6 +862,7 @@ func (n *idMapnode) rebalanceAfterRemove(gap idMapGapIterator) idMapGapIterator
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return idMapGapIterator{p, gap.index}
 			}
@@ -832,10 +909,146 @@ func (n *idMapnode) rebalanceAfterRemove(gap idMapGapIterator) idMapGapIterator
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if idMaptrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *idMapnode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *idMapnode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *idMapnode) calculateMaxGapLeaf() uint32 {
+	max := idMapGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (idMapGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *idMapnode) calculateMaxGapInternal() uint32 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *idMapnode) searchFirstLargeEnoughGap(minSize uint32) idMapGapIterator {
+	if n.maxGap.Get() < minSize {
+		return idMapGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := idMapGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *idMapnode) searchLastLargeEnoughGap(minSize uint32) idMapGapIterator {
+	if n.maxGap.Get() < minSize {
+		return idMapGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := idMapGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1141,6 +1354,114 @@ func (gap idMapGapIterator) NextGap() idMapGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap idMapGapIterator) NextLargeEnoughGap(minSize uint32) idMapGapIterator {
+	if idMaptrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap idMapGapIterator) nextLargeEnoughGapHelper(minSize uint32) idMapGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return idMapGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap idMapGapIterator) PrevLargeEnoughGap(minSize uint32) idMapGapIterator {
+	if idMaptrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap idMapGapIterator) prevLargeEnoughGapHelper(minSize uint32) idMapGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return idMapGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1207,7 +1528,15 @@ func (n *idMapnode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if idMaptrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1259,6 +1588,46 @@ func (s *idMapSet) ImportSortedSlices(sds *idMapSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *idMapSet) segmentTestCheck(expectedSegments int, segFunc func(int, idMapRange, uint32) error) error {
+	havePrev := false
+	prev := uint32(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *idMapSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *idMapSet) saveRoot() *idMapSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/kernel/epoll/epoll_list.go b/pkg/sentry/kernel/epoll/epoll_list.go
index a018f7b5c..a018f7b5c 100755..100644
--- a/pkg/sentry/kernel/epoll/epoll_list.go
+++ b/pkg/sentry/kernel/epoll/epoll_list.go
diff --git a/pkg/sentry/kernel/epoll/epoll_state_autogen.go b/pkg/sentry/kernel/epoll/epoll_state_autogen.go
index da3150465..da3150465 100755..100644
--- a/pkg/sentry/kernel/epoll/epoll_state_autogen.go
+++ b/pkg/sentry/kernel/epoll/epoll_state_autogen.go
diff --git a/pkg/sentry/kernel/eventfd/eventfd_state_autogen.go b/pkg/sentry/kernel/eventfd/eventfd_state_autogen.go
index 636d80ea9..636d80ea9 100755..100644
--- a/pkg/sentry/kernel/eventfd/eventfd_state_autogen.go
+++ b/pkg/sentry/kernel/eventfd/eventfd_state_autogen.go
diff --git a/pkg/sentry/kernel/fasync/fasync_state_autogen.go b/pkg/sentry/kernel/fasync/fasync_state_autogen.go
index fdcd48f64..fdcd48f64 100755..100644
--- a/pkg/sentry/kernel/fasync/fasync_state_autogen.go
+++ b/pkg/sentry/kernel/fasync/fasync_state_autogen.go
diff --git a/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go b/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go
index d3fdf09b0..d3fdf09b0 100755..100644
--- a/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go
+++ b/pkg/sentry/kernel/futex/atomicptr_bucket_unsafe.go
diff --git a/pkg/sentry/kernel/futex/futex_state_autogen.go b/pkg/sentry/kernel/futex/futex_state_autogen.go
index 12a0788ff..12a0788ff 100755..100644
--- a/pkg/sentry/kernel/futex/futex_state_autogen.go
+++ b/pkg/sentry/kernel/futex/futex_state_autogen.go
diff --git a/pkg/sentry/kernel/futex/futex_unsafe_state_autogen.go b/pkg/sentry/kernel/futex/futex_unsafe_state_autogen.go
index 7fc038fce..7fc038fce 100755..100644
--- a/pkg/sentry/kernel/futex/futex_unsafe_state_autogen.go
+++ b/pkg/sentry/kernel/futex/futex_unsafe_state_autogen.go
diff --git a/pkg/sentry/kernel/futex/waiter_list.go b/pkg/sentry/kernel/futex/waiter_list.go
index 1b7a92b62..1b7a92b62 100755..100644
--- a/pkg/sentry/kernel/futex/waiter_list.go
+++ b/pkg/sentry/kernel/futex/waiter_list.go
diff --git a/pkg/sentry/kernel/kernel_amd64_state_autogen.go b/pkg/sentry/kernel/kernel_amd64_state_autogen.go
index 12de47ad0..12de47ad0 100755..100644
--- a/pkg/sentry/kernel/kernel_amd64_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_amd64_state_autogen.go
diff --git a/pkg/sentry/kernel/kernel_arm64_state_autogen.go b/pkg/sentry/kernel/kernel_arm64_state_autogen.go
index 3c040d283..3c040d283 100755..100644
--- a/pkg/sentry/kernel/kernel_arm64_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_arm64_state_autogen.go
diff --git a/pkg/sentry/kernel/kernel_opts.go b/pkg/sentry/kernel/kernel_opts.go
index 2e66ec587..2e66ec587 100755..100644
--- a/pkg/sentry/kernel/kernel_opts.go
+++ b/pkg/sentry/kernel/kernel_opts.go
diff --git a/pkg/sentry/kernel/kernel_opts_state_autogen.go b/pkg/sentry/kernel/kernel_opts_state_autogen.go
index 9ed7e27c9..9ed7e27c9 100755..100644
--- a/pkg/sentry/kernel/kernel_opts_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_opts_state_autogen.go
diff --git a/pkg/sentry/kernel/kernel_state_autogen.go b/pkg/sentry/kernel/kernel_state_autogen.go
index 89ac06522..89ac06522 100755..100644
--- a/pkg/sentry/kernel/kernel_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_state_autogen.go
diff --git a/pkg/sentry/kernel/kernel_unsafe_state_autogen.go b/pkg/sentry/kernel/kernel_unsafe_state_autogen.go
index 12130bf74..12130bf74 100755..100644
--- a/pkg/sentry/kernel/kernel_unsafe_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_unsafe_state_autogen.go
diff --git a/pkg/sentry/kernel/memevent/memevent_state_autogen.go b/pkg/sentry/kernel/memevent/memevent_state_autogen.go
index 4a1679fa9..4a1679fa9 100755..100644
--- a/pkg/sentry/kernel/memevent/memevent_state_autogen.go
+++ b/pkg/sentry/kernel/memevent/memevent_state_autogen.go
diff --git a/pkg/sentry/kernel/memevent/memory_events.go b/pkg/sentry/kernel/memevent/memory_events.go
index 200565bb8..200565bb8 100755..100644
--- a/pkg/sentry/kernel/memevent/memory_events.go
+++ b/pkg/sentry/kernel/memevent/memory_events.go
diff --git a/pkg/sentry/kernel/memevent/memory_events_go_proto/memory_events.pb.go b/pkg/sentry/kernel/memevent/memory_events_go_proto/memory_events.pb.go
index f8b857fa9..f8b857fa9 100755..100644
--- a/pkg/sentry/kernel/memevent/memory_events_go_proto/memory_events.pb.go
+++ b/pkg/sentry/kernel/memevent/memory_events_go_proto/memory_events.pb.go
diff --git a/pkg/sentry/kernel/pending_signals_list.go b/pkg/sentry/kernel/pending_signals_list.go
index 2685c631a..2685c631a 100755..100644
--- a/pkg/sentry/kernel/pending_signals_list.go
+++ b/pkg/sentry/kernel/pending_signals_list.go
diff --git a/pkg/sentry/kernel/pipe/pipe.go b/pkg/sentry/kernel/pipe/pipe.go
index 62c8691f1..79645d7d2 100644
--- a/pkg/sentry/kernel/pipe/pipe.go
+++ b/pkg/sentry/kernel/pipe/pipe.go
@@ -207,7 +207,10 @@ func (p *Pipe) read(ctx context.Context, ops readOps) (int64, error) {
 
 	p.mu.Lock()
 	defer p.mu.Unlock()
+	return p.readLocked(ctx, ops)
+}
 
+func (p *Pipe) readLocked(ctx context.Context, ops readOps) (int64, error) {
 	// Is the pipe empty?
 	if p.view.Size() == 0 {
 		if !p.HasWriters() {
@@ -246,7 +249,10 @@ type writeOps struct {
 func (p *Pipe) write(ctx context.Context, ops writeOps) (int64, error) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
+	return p.writeLocked(ctx, ops)
+}
 
+func (p *Pipe) writeLocked(ctx context.Context, ops writeOps) (int64, error) {
 	// Can't write to a pipe with no readers.
 	if !p.HasReaders() {
 		return 0, syscall.EPIPE
diff --git a/pkg/sentry/kernel/pipe/pipe_state_autogen.go b/pkg/sentry/kernel/pipe/pipe_state_autogen.go
index b49ab46f9..b49ab46f9 100755..100644
--- a/pkg/sentry/kernel/pipe/pipe_state_autogen.go
+++ b/pkg/sentry/kernel/pipe/pipe_state_autogen.go
diff --git a/pkg/sentry/fsimpl/gofer/pagemath.go b/pkg/sentry/kernel/pipe/pipe_unsafe.go
index 847cb0784..dd60cba24 100755..100644
--- a/pkg/sentry/fsimpl/gofer/pagemath.go
+++ b/pkg/sentry/kernel/pipe/pipe_unsafe.go
@@ -12,20 +12,24 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package gofer
+package pipe
 
 import (
-	"gvisor.dev/gvisor/pkg/usermem"
+	"unsafe"
 )
 
-// This are equivalent to usermem.Addr.RoundDown/Up, but without the
-// potentially truncating conversion to usermem.Addr. This is necessary because
-// there is no way to define generic "PageRoundDown/Up" functions in Go.
-
-func pageRoundDown(x uint64) uint64 {
-	return x &^ (usermem.PageSize - 1)
-}
-
-func pageRoundUp(x uint64) uint64 {
-	return pageRoundDown(x + usermem.PageSize - 1)
+// lockTwoPipes locks both x.mu and y.mu in an order that is guaranteed to be
+// consistent for both lockTwoPipes(x, y) and lockTwoPipes(y, x), such that
+// concurrent calls cannot deadlock.
+//
+// Preconditions: x != y.
+func lockTwoPipes(x, y *Pipe) {
+	// Lock the two pipes in order of increasing address.
+	if uintptr(unsafe.Pointer(x)) < uintptr(unsafe.Pointer(y)) {
+		x.mu.Lock()
+		y.mu.Lock()
+	} else {
+		y.mu.Lock()
+		x.mu.Lock()
+	}
 }
diff --git a/pkg/log/log_state_autogen.go b/pkg/sentry/kernel/pipe/pipe_unsafe_state_autogen.go
index 4e243c216..d3b40feb4 100755..100644
--- a/pkg/log/log_state_autogen.go
+++ b/pkg/sentry/kernel/pipe/pipe_unsafe_state_autogen.go
@@ -1,3 +1,3 @@
 // automatically generated by stateify.
 
-package log
+package pipe
diff --git a/pkg/sentry/kernel/pipe/pipe_util.go b/pkg/sentry/kernel/pipe/pipe_util.go
index aacf28da2..aacf28da2 100755..100644
--- a/pkg/sentry/kernel/pipe/pipe_util.go
+++ b/pkg/sentry/kernel/pipe/pipe_util.go
diff --git a/pkg/sentry/kernel/pipe/vfs.go b/pkg/sentry/kernel/pipe/vfs.go
index b54f08a30..2602bed72 100755..100644
--- a/pkg/sentry/kernel/pipe/vfs.go
+++ b/pkg/sentry/kernel/pipe/vfs.go
@@ -16,7 +16,9 @@ package pipe
 
 import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/buffer"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
@@ -150,7 +152,9 @@ func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) *
 	return &fd.vfsfd
 }
 
-// VFSPipeFD implements vfs.FileDescriptionImpl for pipes.
+// VFSPipeFD implements vfs.FileDescriptionImpl for pipes. It also implements
+// non-atomic usermem.IO methods, allowing it to be passed as usermem.IO to
+// other FileDescriptions for splice(2) and tee(2).
 type VFSPipeFD struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
@@ -229,3 +233,216 @@ func (fd *VFSPipeFD) PipeSize() int64 {
 func (fd *VFSPipeFD) SetPipeSize(size int64) (int64, error) {
 	return fd.pipe.SetFifoSize(size)
 }
+
+// IOSequence returns a useremm.IOSequence that reads up to count bytes from,
+// or writes up to count bytes to, fd.
+func (fd *VFSPipeFD) IOSequence(count int64) usermem.IOSequence {
+	return usermem.IOSequence{
+		IO:    fd,
+		Addrs: usermem.AddrRangeSeqOf(usermem.AddrRange{0, usermem.Addr(count)}),
+	}
+}
+
+// CopyIn implements usermem.IO.CopyIn.
+func (fd *VFSPipeFD) CopyIn(ctx context.Context, addr usermem.Addr, dst []byte, opts usermem.IOOpts) (int, error) {
+	origCount := int64(len(dst))
+	n, err := fd.pipe.read(ctx, readOps{
+		left: func() int64 {
+			return int64(len(dst))
+		},
+		limit: func(l int64) {
+			dst = dst[:l]
+		},
+		read: func(view *buffer.View) (int64, error) {
+			n, err := view.ReadAt(dst, 0)
+			view.TrimFront(int64(n))
+			return int64(n), err
+		},
+	})
+	if n > 0 {
+		fd.pipe.Notify(waiter.EventOut)
+	}
+	if err == nil && n != origCount {
+		return int(n), syserror.ErrWouldBlock
+	}
+	return int(n), err
+}
+
+// CopyOut implements usermem.IO.CopyOut.
+func (fd *VFSPipeFD) CopyOut(ctx context.Context, addr usermem.Addr, src []byte, opts usermem.IOOpts) (int, error) {
+	origCount := int64(len(src))
+	n, err := fd.pipe.write(ctx, writeOps{
+		left: func() int64 {
+			return int64(len(src))
+		},
+		limit: func(l int64) {
+			src = src[:l]
+		},
+		write: func(view *buffer.View) (int64, error) {
+			view.Append(src)
+			return int64(len(src)), nil
+		},
+	})
+	if n > 0 {
+		fd.pipe.Notify(waiter.EventIn)
+	}
+	if err == nil && n != origCount {
+		return int(n), syserror.ErrWouldBlock
+	}
+	return int(n), err
+}
+
+// ZeroOut implements usermem.IO.ZeroOut.
+func (fd *VFSPipeFD) ZeroOut(ctx context.Context, addr usermem.Addr, toZero int64, opts usermem.IOOpts) (int64, error) {
+	origCount := toZero
+	n, err := fd.pipe.write(ctx, writeOps{
+		left: func() int64 {
+			return toZero
+		},
+		limit: func(l int64) {
+			toZero = l
+		},
+		write: func(view *buffer.View) (int64, error) {
+			view.Grow(view.Size()+toZero, true /* zero */)
+			return toZero, nil
+		},
+	})
+	if n > 0 {
+		fd.pipe.Notify(waiter.EventIn)
+	}
+	if err == nil && n != origCount {
+		return n, syserror.ErrWouldBlock
+	}
+	return n, err
+}
+
+// CopyInTo implements usermem.IO.CopyInTo.
+func (fd *VFSPipeFD) CopyInTo(ctx context.Context, ars usermem.AddrRangeSeq, dst safemem.Writer, opts usermem.IOOpts) (int64, error) {
+	count := ars.NumBytes()
+	if count == 0 {
+		return 0, nil
+	}
+	origCount := count
+	n, err := fd.pipe.read(ctx, readOps{
+		left: func() int64 {
+			return count
+		},
+		limit: func(l int64) {
+			count = l
+		},
+		read: func(view *buffer.View) (int64, error) {
+			n, err := view.ReadToSafememWriter(dst, uint64(count))
+			view.TrimFront(int64(n))
+			return int64(n), err
+		},
+	})
+	if n > 0 {
+		fd.pipe.Notify(waiter.EventOut)
+	}
+	if err == nil && n != origCount {
+		return n, syserror.ErrWouldBlock
+	}
+	return n, err
+}
+
+// CopyOutFrom implements usermem.IO.CopyOutFrom.
+func (fd *VFSPipeFD) CopyOutFrom(ctx context.Context, ars usermem.AddrRangeSeq, src safemem.Reader, opts usermem.IOOpts) (int64, error) {
+	count := ars.NumBytes()
+	if count == 0 {
+		return 0, nil
+	}
+	origCount := count
+	n, err := fd.pipe.write(ctx, writeOps{
+		left: func() int64 {
+			return count
+		},
+		limit: func(l int64) {
+			count = l
+		},
+		write: func(view *buffer.View) (int64, error) {
+			n, err := view.WriteFromSafememReader(src, uint64(count))
+			return int64(n), err
+		},
+	})
+	if n > 0 {
+		fd.pipe.Notify(waiter.EventIn)
+	}
+	if err == nil && n != origCount {
+		return n, syserror.ErrWouldBlock
+	}
+	return n, err
+}
+
+// SwapUint32 implements usermem.IO.SwapUint32.
+func (fd *VFSPipeFD) SwapUint32(ctx context.Context, addr usermem.Addr, new uint32, opts usermem.IOOpts) (uint32, error) {
+	// How did a pipe get passed as the virtual address space to futex(2)?
+	panic("VFSPipeFD.SwapUint32 called unexpectedly")
+}
+
+// CompareAndSwapUint32 implements usermem.IO.CompareAndSwapUint32.
+func (fd *VFSPipeFD) CompareAndSwapUint32(ctx context.Context, addr usermem.Addr, old, new uint32, opts usermem.IOOpts) (uint32, error) {
+	panic("VFSPipeFD.CompareAndSwapUint32 called unexpectedly")
+}
+
+// LoadUint32 implements usermem.IO.LoadUint32.
+func (fd *VFSPipeFD) LoadUint32(ctx context.Context, addr usermem.Addr, opts usermem.IOOpts) (uint32, error) {
+	panic("VFSPipeFD.LoadUint32 called unexpectedly")
+}
+
+// Splice reads up to count bytes from src and writes them to dst. It returns
+// the number of bytes moved.
+//
+// Preconditions: count > 0.
+func Splice(ctx context.Context, dst, src *VFSPipeFD, count int64) (int64, error) {
+	return spliceOrTee(ctx, dst, src, count, true /* removeFromSrc */)
+}
+
+// Tee reads up to count bytes from src and writes them to dst, without
+// removing the read bytes from src. It returns the number of bytes copied.
+//
+// Preconditions: count > 0.
+func Tee(ctx context.Context, dst, src *VFSPipeFD, count int64) (int64, error) {
+	return spliceOrTee(ctx, dst, src, count, false /* removeFromSrc */)
+}
+
+// Preconditions: count > 0.
+func spliceOrTee(ctx context.Context, dst, src *VFSPipeFD, count int64, removeFromSrc bool) (int64, error) {
+	if dst.pipe == src.pipe {
+		return 0, syserror.EINVAL
+	}
+
+	lockTwoPipes(dst.pipe, src.pipe)
+	defer dst.pipe.mu.Unlock()
+	defer src.pipe.mu.Unlock()
+
+	n, err := dst.pipe.writeLocked(ctx, writeOps{
+		left: func() int64 {
+			return count
+		},
+		limit: func(l int64) {
+			count = l
+		},
+		write: func(dstView *buffer.View) (int64, error) {
+			return src.pipe.readLocked(ctx, readOps{
+				left: func() int64 {
+					return count
+				},
+				limit: func(l int64) {
+					count = l
+				},
+				read: func(srcView *buffer.View) (int64, error) {
+					n, err := srcView.ReadToSafememWriter(dstView, uint64(count))
+					if n > 0 && removeFromSrc {
+						srcView.TrimFront(int64(n))
+					}
+					return int64(n), err
+				},
+			})
+		},
+	})
+	if n > 0 {
+		dst.pipe.Notify(waiter.EventIn)
+		src.pipe.Notify(waiter.EventOut)
+	}
+	return n, err
+}
diff --git a/pkg/sentry/kernel/process_group_list.go b/pkg/sentry/kernel/process_group_list.go
index 3c5ea8aa7..3c5ea8aa7 100755..100644
--- a/pkg/sentry/kernel/process_group_list.go
+++ b/pkg/sentry/kernel/process_group_list.go
diff --git a/pkg/sentry/kernel/sched/sched_state_autogen.go b/pkg/sentry/kernel/sched/sched_state_autogen.go
index 9705ca79d..9705ca79d 100755..100644
--- a/pkg/sentry/kernel/sched/sched_state_autogen.go
+++ b/pkg/sentry/kernel/sched/sched_state_autogen.go
diff --git a/pkg/sentry/kernel/semaphore/semaphore_state_autogen.go b/pkg/sentry/kernel/semaphore/semaphore_state_autogen.go
index ba1d073d9..ba1d073d9 100755..100644
--- a/pkg/sentry/kernel/semaphore/semaphore_state_autogen.go
+++ b/pkg/sentry/kernel/semaphore/semaphore_state_autogen.go
diff --git a/pkg/sentry/kernel/semaphore/waiter_list.go b/pkg/sentry/kernel/semaphore/waiter_list.go
index 4bfe5ff95..4bfe5ff95 100755..100644
--- a/pkg/sentry/kernel/semaphore/waiter_list.go
+++ b/pkg/sentry/kernel/semaphore/waiter_list.go
diff --git a/pkg/sentry/kernel/seqatomic_taskgoroutineschedinfo_unsafe.go b/pkg/sentry/kernel/seqatomic_taskgoroutineschedinfo_unsafe.go
index b133423cc..950645965 100755..100644
--- a/pkg/sentry/kernel/seqatomic_taskgoroutineschedinfo_unsafe.go
+++ b/pkg/sentry/kernel/seqatomic_taskgoroutineschedinfo_unsafe.go
@@ -1,11 +1,11 @@
 package kernel
 
 import (
+	"fmt"
 	"reflect"
 	"strings"
 	"unsafe"
 
-	"fmt"
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
diff --git a/pkg/sentry/kernel/session_list.go b/pkg/sentry/kernel/session_list.go
index 768482ab6..768482ab6 100755..100644
--- a/pkg/sentry/kernel/session_list.go
+++ b/pkg/sentry/kernel/session_list.go
diff --git a/pkg/sentry/kernel/shm/shm_state_autogen.go b/pkg/sentry/kernel/shm/shm_state_autogen.go
index fa8f896f7..fa8f896f7 100755..100644
--- a/pkg/sentry/kernel/shm/shm_state_autogen.go
+++ b/pkg/sentry/kernel/shm/shm_state_autogen.go
diff --git a/pkg/sentry/kernel/signalfd/signalfd.go b/pkg/sentry/kernel/signalfd/signalfd.go
index 8243bb93e..8243bb93e 100755..100644
--- a/pkg/sentry/kernel/signalfd/signalfd.go
+++ b/pkg/sentry/kernel/signalfd/signalfd.go
diff --git a/pkg/sentry/kernel/signalfd/signalfd_state_autogen.go b/pkg/sentry/kernel/signalfd/signalfd_state_autogen.go
index 2ab5b4702..2ab5b4702 100755..100644
--- a/pkg/sentry/kernel/signalfd/signalfd_state_autogen.go
+++ b/pkg/sentry/kernel/signalfd/signalfd_state_autogen.go
diff --git a/pkg/sentry/kernel/socket_list.go b/pkg/sentry/kernel/socket_list.go
index 294aa99fe..294aa99fe 100755..100644
--- a/pkg/sentry/kernel/socket_list.go
+++ b/pkg/sentry/kernel/socket_list.go
diff --git a/pkg/sentry/kernel/task_list.go b/pkg/sentry/kernel/task_list.go
index e7a3a3d20..e7a3a3d20 100755..100644
--- a/pkg/sentry/kernel/task_list.go
+++ b/pkg/sentry/kernel/task_list.go
diff --git a/pkg/sentry/kernel/time/time_state_autogen.go b/pkg/sentry/kernel/time/time_state_autogen.go
index ab6c6633d..ab6c6633d 100755..100644
--- a/pkg/sentry/kernel/time/time_state_autogen.go
+++ b/pkg/sentry/kernel/time/time_state_autogen.go
diff --git a/pkg/sentry/kernel/tty.go b/pkg/sentry/kernel/tty.go
index d0e0810e8..d0e0810e8 100755..100644
--- a/pkg/sentry/kernel/tty.go
+++ b/pkg/sentry/kernel/tty.go
diff --git a/pkg/sentry/kernel/uncaught_signal_go_proto/uncaught_signal.pb.go b/pkg/sentry/kernel/uncaught_signal_go_proto/uncaught_signal.pb.go
index 822e549ab..822e549ab 100755..100644
--- a/pkg/sentry/kernel/uncaught_signal_go_proto/uncaught_signal.pb.go
+++ b/pkg/sentry/kernel/uncaught_signal_go_proto/uncaught_signal.pb.go
diff --git a/pkg/sentry/limits/limits_state_autogen.go b/pkg/sentry/limits/limits_state_autogen.go
index aa42533a9..aa42533a9 100755..100644
--- a/pkg/sentry/limits/limits_state_autogen.go
+++ b/pkg/sentry/limits/limits_state_autogen.go
diff --git a/pkg/sentry/loader/loader_state_autogen.go b/pkg/sentry/loader/loader_state_autogen.go
index e28667944..e28667944 100755..100644
--- a/pkg/sentry/loader/loader_state_autogen.go
+++ b/pkg/sentry/loader/loader_state_autogen.go
diff --git a/pkg/sentry/loader/vdso_bin.go b/pkg/sentry/loader/vdso_bin.go
index 95a8cd8cc..595e2a1af 100755..100644
--- a/pkg/sentry/loader/vdso_bin.go
+++ b/pkg/sentry/loader/vdso_bin.go
@@ -2,4 +2,4 @@
 
 package loader
 
-var vdsoBin = []byte("ELF

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\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00p\xff\xff\xff\xff\xff\x00\x00p\xff\xff\xff\xff\xff\x93\x00\x00\x00\x00\x00\x00\x93\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xa0\x00\x00\x00\x00\x00\x00\xa0p\xff\xff\xff\xff\xff\xa0p\xff\xff\xff\xff\xff
\x00\x00\x00\x00\x00\x00
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\x00
\x00
\x00
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\x00\x00\x00\x00\x00\x00
\x00\x00\x00\x00\x00\x00\x00
\x00\x00\x00\x00
\x00\xf6u\xae\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
;D\x00\x00\x00\x00\x00\x00\x00
\x00\x00`\x00\x00\x00
\x00\x00x\x00\x00\x00@
\x00\x00\x90\x00\x00\x00\xa0
\x00\x00\xb8\x00\x00\x00\xd0
\x00\x00\xd8\x00\x00\x00\xe0
\x00\x00\xf0\x00\x00\x00\x80\x00\x00
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
zR\x00
x
\x90
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\xd1L\x89\xc8H\xc1\xe8	H\xb9SZ\x9b\xa0/\xb8D\x00H\xf7\xe1H\xc1\xeaHi\xc2\x00ʚ;I)\xc1I\x89M\x89H1\xc0[ÿ
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p\xff\xff\xff\xff\xff 
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p\xff\xff\xff\xff\xff`
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+var vdsoBin = []byte("ELF

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zR\x00
x
\x90
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diff --git a/pkg/sentry/memmap/mappable_range.go b/pkg/sentry/memmap/mappable_range.go
index 6b6c2c685..6b6c2c685 100755..100644
--- a/pkg/sentry/memmap/mappable_range.go
+++ b/pkg/sentry/memmap/mappable_range.go
diff --git a/pkg/sentry/memmap/mapping_set_impl.go b/pkg/sentry/memmap/mapping_set_impl.go
index e632f28a5..cb4281950 100755..100644
--- a/pkg/sentry/memmap/mapping_set_impl.go
+++ b/pkg/sentry/memmap/mapping_set_impl.go
@@ -5,6 +5,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const MappingtrackGaps = 0
+
+var _ = uint8(MappingtrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type MappingdynamicGap [MappingtrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *MappingdynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *MappingdynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -263,8 +291,12 @@ func (s *MappingSet) Insert(gap MappingGapIterator, r MappableRange, val Mapping
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (mappingSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := MappingtrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (mappingSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -278,11 +310,16 @@ func (s *MappingSet) Insert(gap MappingGapIterator, r MappableRange, val Mapping
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (mappingSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := MappingtrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -309,11 +346,15 @@ func (s *MappingSet) InsertWithoutMerging(gap MappingGapIterator, r MappableRang
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *MappingSet) InsertWithoutMergingUnchecked(gap MappingGapIterator, r MappableRange, val MappingsOfRange) MappingIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := MappingtrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return MappingIterator{gap.node, gap.index}
 }
 
@@ -328,12 +369,20 @@ func (s *MappingSet) Remove(seg MappingIterator) MappingGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if MappingtrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	mappingSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if MappingtrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(MappingGapIterator{seg.node, seg.index})
 }
 
@@ -383,6 +432,7 @@ func (s *MappingSet) MergeUnchecked(first, second MappingIterator) MappingIterat
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -558,6 +608,12 @@ type Mappingnode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap MappingdynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [MappingmaxDegree - 1]MappableRange
@@ -603,12 +659,12 @@ func (n *Mappingnode) nextSibling() *Mappingnode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *Mappingnode) rebalanceBeforeInsert(gap MappingGapIterator) MappingGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < MappingmaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &Mappingnode{
@@ -644,6 +700,11 @@ func (n *Mappingnode) rebalanceBeforeInsert(gap MappingGapIterator) MappingGapIt
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if MappingtrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -681,6 +742,11 @@ func (n *Mappingnode) rebalanceBeforeInsert(gap MappingGapIterator) MappingGapIt
 	}
 	n.nrSegments = MappingminDegree - 1
 
+	if MappingtrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -726,6 +792,11 @@ func (n *Mappingnode) rebalanceAfterRemove(gap MappingGapIterator) MappingGapIte
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if MappingtrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return MappingGapIterator{n, 0}
 			}
@@ -754,6 +825,11 @@ func (n *Mappingnode) rebalanceAfterRemove(gap MappingGapIterator) MappingGapIte
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if MappingtrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return MappingGapIterator{n, n.nrSegments}
@@ -786,6 +862,7 @@ func (n *Mappingnode) rebalanceAfterRemove(gap MappingGapIterator) MappingGapIte
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return MappingGapIterator{p, gap.index}
 			}
@@ -832,10 +909,146 @@ func (n *Mappingnode) rebalanceAfterRemove(gap MappingGapIterator) MappingGapIte
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if MappingtrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *Mappingnode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *Mappingnode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *Mappingnode) calculateMaxGapLeaf() uint64 {
+	max := MappingGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (MappingGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *Mappingnode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *Mappingnode) searchFirstLargeEnoughGap(minSize uint64) MappingGapIterator {
+	if n.maxGap.Get() < minSize {
+		return MappingGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := MappingGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *Mappingnode) searchLastLargeEnoughGap(minSize uint64) MappingGapIterator {
+	if n.maxGap.Get() < minSize {
+		return MappingGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := MappingGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1141,6 +1354,114 @@ func (gap MappingGapIterator) NextGap() MappingGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap MappingGapIterator) NextLargeEnoughGap(minSize uint64) MappingGapIterator {
+	if MappingtrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap MappingGapIterator) nextLargeEnoughGapHelper(minSize uint64) MappingGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return MappingGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap MappingGapIterator) PrevLargeEnoughGap(minSize uint64) MappingGapIterator {
+	if MappingtrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap MappingGapIterator) prevLargeEnoughGapHelper(minSize uint64) MappingGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return MappingGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1207,7 +1528,15 @@ func (n *Mappingnode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if MappingtrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1259,6 +1588,46 @@ func (s *MappingSet) ImportSortedSlices(sds *MappingSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *MappingSet) segmentTestCheck(expectedSegments int, segFunc func(int, MappableRange, MappingsOfRange) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *MappingSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *MappingSet) saveRoot() *MappingSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/memmap/memmap_impl_state_autogen.go b/pkg/sentry/memmap/memmap_impl_state_autogen.go
index b231fd9c3..b66b03884 100755..100644
--- a/pkg/sentry/memmap/memmap_impl_state_autogen.go
+++ b/pkg/sentry/memmap/memmap_impl_state_autogen.go
@@ -25,6 +25,7 @@ func (x *Mappingnode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -36,6 +37,7 @@ func (x *Mappingnode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
diff --git a/pkg/sentry/memmap/memmap_state_autogen.go b/pkg/sentry/memmap/memmap_state_autogen.go
index 2072dbad2..2072dbad2 100755..100644
--- a/pkg/sentry/memmap/memmap_state_autogen.go
+++ b/pkg/sentry/memmap/memmap_state_autogen.go
diff --git a/pkg/sentry/mm/file_refcount_set.go b/pkg/sentry/mm/file_refcount_set.go
index 6b3081009..475c73fee 100755..100644
--- a/pkg/sentry/mm/file_refcount_set.go
+++ b/pkg/sentry/mm/file_refcount_set.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const fileRefcounttrackGaps = 0
+
+var _ = uint8(fileRefcounttrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type fileRefcountdynamicGap [fileRefcounttrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *fileRefcountdynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *fileRefcountdynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *fileRefcountSet) Insert(gap fileRefcountGapIterator, r __generics_impor
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (fileRefcountSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := fileRefcounttrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (fileRefcountSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *fileRefcountSet) Insert(gap fileRefcountGapIterator, r __generics_impor
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (fileRefcountSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := fileRefcounttrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *fileRefcountSet) InsertWithoutMerging(gap fileRefcountGapIterator, r __
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *fileRefcountSet) InsertWithoutMergingUnchecked(gap fileRefcountGapIterator, r __generics_imported0.FileRange, val int32) fileRefcountIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := fileRefcounttrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return fileRefcountIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *fileRefcountSet) Remove(seg fileRefcountIterator) fileRefcountGapIterat
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if fileRefcounttrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	fileRefcountSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if fileRefcounttrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(fileRefcountGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *fileRefcountSet) MergeUnchecked(first, second fileRefcountIterator) fil
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type fileRefcountnode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap fileRefcountdynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [fileRefcountmaxDegree - 1]__generics_imported0.FileRange
@@ -607,12 +663,12 @@ func (n *fileRefcountnode) nextSibling() *fileRefcountnode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *fileRefcountnode) rebalanceBeforeInsert(gap fileRefcountGapIterator) fileRefcountGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < fileRefcountmaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &fileRefcountnode{
@@ -648,6 +704,11 @@ func (n *fileRefcountnode) rebalanceBeforeInsert(gap fileRefcountGapIterator) fi
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if fileRefcounttrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *fileRefcountnode) rebalanceBeforeInsert(gap fileRefcountGapIterator) fi
 	}
 	n.nrSegments = fileRefcountminDegree - 1
 
+	if fileRefcounttrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *fileRefcountnode) rebalanceAfterRemove(gap fileRefcountGapIterator) fil
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if fileRefcounttrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return fileRefcountGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *fileRefcountnode) rebalanceAfterRemove(gap fileRefcountGapIterator) fil
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if fileRefcounttrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return fileRefcountGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *fileRefcountnode) rebalanceAfterRemove(gap fileRefcountGapIterator) fil
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return fileRefcountGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *fileRefcountnode) rebalanceAfterRemove(gap fileRefcountGapIterator) fil
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if fileRefcounttrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *fileRefcountnode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *fileRefcountnode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *fileRefcountnode) calculateMaxGapLeaf() uint64 {
+	max := fileRefcountGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (fileRefcountGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *fileRefcountnode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *fileRefcountnode) searchFirstLargeEnoughGap(minSize uint64) fileRefcountGapIterator {
+	if n.maxGap.Get() < minSize {
+		return fileRefcountGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := fileRefcountGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *fileRefcountnode) searchLastLargeEnoughGap(minSize uint64) fileRefcountGapIterator {
+	if n.maxGap.Get() < minSize {
+		return fileRefcountGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := fileRefcountGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap fileRefcountGapIterator) NextGap() fileRefcountGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap fileRefcountGapIterator) NextLargeEnoughGap(minSize uint64) fileRefcountGapIterator {
+	if fileRefcounttrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap fileRefcountGapIterator) nextLargeEnoughGapHelper(minSize uint64) fileRefcountGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return fileRefcountGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap fileRefcountGapIterator) PrevLargeEnoughGap(minSize uint64) fileRefcountGapIterator {
+	if fileRefcounttrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap fileRefcountGapIterator) prevLargeEnoughGapHelper(minSize uint64) fileRefcountGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return fileRefcountGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *fileRefcountnode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if fileRefcounttrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *fileRefcountSet) ImportSortedSlices(sds *fileRefcountSegmentDataSlices)
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *fileRefcountSet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.FileRange, int32) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *fileRefcountSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *fileRefcountSet) saveRoot() *fileRefcountSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/mm/io_list.go b/pkg/sentry/mm/io_list.go
index ae0f19fc5..ae0f19fc5 100755..100644
--- a/pkg/sentry/mm/io_list.go
+++ b/pkg/sentry/mm/io_list.go
diff --git a/pkg/sentry/mm/mm_state_autogen.go b/pkg/sentry/mm/mm_state_autogen.go
index 4ef8fa9c6..fde35bcd8 100755..100644
--- a/pkg/sentry/mm/mm_state_autogen.go
+++ b/pkg/sentry/mm/mm_state_autogen.go
@@ -82,6 +82,7 @@ func (x *fileRefcountnode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -93,6 +94,7 @@ func (x *fileRefcountnode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
@@ -276,6 +278,7 @@ func (x *pmanode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -287,6 +290,7 @@ func (x *pmanode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
@@ -343,6 +347,7 @@ func (x *vmanode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -354,6 +359,7 @@ func (x *vmanode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
diff --git a/pkg/sentry/mm/pma_set.go b/pkg/sentry/mm/pma_set.go
index 8906e4edc..d0cc1f9d3 100755..100644
--- a/pkg/sentry/mm/pma_set.go
+++ b/pkg/sentry/mm/pma_set.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const pmatrackGaps = 0
+
+var _ = uint8(pmatrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type pmadynamicGap [pmatrackGaps]__generics_imported0.Addr
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *pmadynamicGap) Get() __generics_imported0.Addr {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *pmadynamicGap) Set(v __generics_imported0.Addr) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *pmaSet) Insert(gap pmaGapIterator, r __generics_imported0.AddrRange, va
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (pmaSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := pmatrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (pmaSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *pmaSet) Insert(gap pmaGapIterator, r __generics_imported0.AddrRange, va
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (pmaSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := pmatrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *pmaSet) InsertWithoutMerging(gap pmaGapIterator, r __generics_imported0
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *pmaSet) InsertWithoutMergingUnchecked(gap pmaGapIterator, r __generics_imported0.AddrRange, val pma) pmaIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := pmatrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return pmaIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *pmaSet) Remove(seg pmaIterator) pmaGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if pmatrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	pmaSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if pmatrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(pmaGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *pmaSet) MergeUnchecked(first, second pmaIterator) pmaIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type pmanode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap pmadynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [pmamaxDegree - 1]__generics_imported0.AddrRange
@@ -607,12 +663,12 @@ func (n *pmanode) nextSibling() *pmanode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *pmanode) rebalanceBeforeInsert(gap pmaGapIterator) pmaGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < pmamaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &pmanode{
@@ -648,6 +704,11 @@ func (n *pmanode) rebalanceBeforeInsert(gap pmaGapIterator) pmaGapIterator {
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if pmatrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *pmanode) rebalanceBeforeInsert(gap pmaGapIterator) pmaGapIterator {
 	}
 	n.nrSegments = pmaminDegree - 1
 
+	if pmatrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *pmanode) rebalanceAfterRemove(gap pmaGapIterator) pmaGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if pmatrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return pmaGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *pmanode) rebalanceAfterRemove(gap pmaGapIterator) pmaGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if pmatrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return pmaGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *pmanode) rebalanceAfterRemove(gap pmaGapIterator) pmaGapIterator {
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return pmaGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *pmanode) rebalanceAfterRemove(gap pmaGapIterator) pmaGapIterator {
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if pmatrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *pmanode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *pmanode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *pmanode) calculateMaxGapLeaf() __generics_imported0.Addr {
+	max := pmaGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (pmaGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *pmanode) calculateMaxGapInternal() __generics_imported0.Addr {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *pmanode) searchFirstLargeEnoughGap(minSize __generics_imported0.Addr) pmaGapIterator {
+	if n.maxGap.Get() < minSize {
+		return pmaGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := pmaGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *pmanode) searchLastLargeEnoughGap(minSize __generics_imported0.Addr) pmaGapIterator {
+	if n.maxGap.Get() < minSize {
+		return pmaGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := pmaGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap pmaGapIterator) NextGap() pmaGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap pmaGapIterator) NextLargeEnoughGap(minSize __generics_imported0.Addr) pmaGapIterator {
+	if pmatrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap pmaGapIterator) nextLargeEnoughGapHelper(minSize __generics_imported0.Addr) pmaGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return pmaGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap pmaGapIterator) PrevLargeEnoughGap(minSize __generics_imported0.Addr) pmaGapIterator {
+	if pmatrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap pmaGapIterator) prevLargeEnoughGapHelper(minSize __generics_imported0.Addr) pmaGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return pmaGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *pmanode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if pmatrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *pmaSet) ImportSortedSlices(sds *pmaSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *pmaSet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.AddrRange, pma) error) error {
+	havePrev := false
+	prev := __generics_imported0.Addr(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *pmaSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *pmaSet) saveRoot() *pmaSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/mm/vma.go b/pkg/sentry/mm/vma.go
index 9a14e69e6..16d8207e9 100644
--- a/pkg/sentry/mm/vma.go
+++ b/pkg/sentry/mm/vma.go
@@ -195,7 +195,7 @@ func (mm *MemoryManager) applicationAddrRange() usermem.AddrRange {
 
 // Preconditions: mm.mappingMu must be locked.
 func (mm *MemoryManager) findLowestAvailableLocked(length, alignment uint64, bounds usermem.AddrRange) (usermem.Addr, error) {
-	for gap := mm.vmas.LowerBoundGap(bounds.Start); gap.Ok() && gap.Start() < bounds.End; gap = gap.NextGap() {
+	for gap := mm.vmas.LowerBoundGap(bounds.Start); gap.Ok() && gap.Start() < bounds.End; gap = gap.NextLargeEnoughGap(usermem.Addr(length)) {
 		if gr := gap.availableRange().Intersect(bounds); uint64(gr.Length()) >= length {
 			// Can we shift up to match the alignment?
 			if offset := uint64(gr.Start) % alignment; offset != 0 {
@@ -214,7 +214,7 @@ func (mm *MemoryManager) findLowestAvailableLocked(length, alignment uint64, bou
 
 // Preconditions: mm.mappingMu must be locked.
 func (mm *MemoryManager) findHighestAvailableLocked(length, alignment uint64, bounds usermem.AddrRange) (usermem.Addr, error) {
-	for gap := mm.vmas.UpperBoundGap(bounds.End); gap.Ok() && gap.End() > bounds.Start; gap = gap.PrevGap() {
+	for gap := mm.vmas.UpperBoundGap(bounds.End); gap.Ok() && gap.End() > bounds.Start; gap = gap.PrevLargeEnoughGap(usermem.Addr(length)) {
 		if gr := gap.availableRange().Intersect(bounds); uint64(gr.Length()) >= length {
 			// Can we shift down to match the alignment?
 			start := gr.End - usermem.Addr(length)
diff --git a/pkg/sentry/mm/vma_set.go b/pkg/sentry/mm/vma_set.go
index af6b1d317..e515ef105 100755..100644
--- a/pkg/sentry/mm/vma_set.go
+++ b/pkg/sentry/mm/vma_set.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const vmatrackGaps = 1
+
+var _ = uint8(vmatrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type vmadynamicGap [vmatrackGaps]__generics_imported0.Addr
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *vmadynamicGap) Get() __generics_imported0.Addr {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *vmadynamicGap) Set(v __generics_imported0.Addr) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *vmaSet) Insert(gap vmaGapIterator, r __generics_imported0.AddrRange, va
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (vmaSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := vmatrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (vmaSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *vmaSet) Insert(gap vmaGapIterator, r __generics_imported0.AddrRange, va
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (vmaSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := vmatrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *vmaSet) InsertWithoutMerging(gap vmaGapIterator, r __generics_imported0
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *vmaSet) InsertWithoutMergingUnchecked(gap vmaGapIterator, r __generics_imported0.AddrRange, val vma) vmaIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := vmatrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return vmaIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *vmaSet) Remove(seg vmaIterator) vmaGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if vmatrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	vmaSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if vmatrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(vmaGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *vmaSet) MergeUnchecked(first, second vmaIterator) vmaIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type vmanode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap vmadynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [vmamaxDegree - 1]__generics_imported0.AddrRange
@@ -607,12 +663,12 @@ func (n *vmanode) nextSibling() *vmanode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *vmanode) rebalanceBeforeInsert(gap vmaGapIterator) vmaGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < vmamaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &vmanode{
@@ -648,6 +704,11 @@ func (n *vmanode) rebalanceBeforeInsert(gap vmaGapIterator) vmaGapIterator {
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if vmatrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *vmanode) rebalanceBeforeInsert(gap vmaGapIterator) vmaGapIterator {
 	}
 	n.nrSegments = vmaminDegree - 1
 
+	if vmatrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *vmanode) rebalanceAfterRemove(gap vmaGapIterator) vmaGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if vmatrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return vmaGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *vmanode) rebalanceAfterRemove(gap vmaGapIterator) vmaGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if vmatrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return vmaGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *vmanode) rebalanceAfterRemove(gap vmaGapIterator) vmaGapIterator {
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return vmaGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *vmanode) rebalanceAfterRemove(gap vmaGapIterator) vmaGapIterator {
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if vmatrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *vmanode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *vmanode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *vmanode) calculateMaxGapLeaf() __generics_imported0.Addr {
+	max := vmaGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (vmaGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *vmanode) calculateMaxGapInternal() __generics_imported0.Addr {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *vmanode) searchFirstLargeEnoughGap(minSize __generics_imported0.Addr) vmaGapIterator {
+	if n.maxGap.Get() < minSize {
+		return vmaGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := vmaGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *vmanode) searchLastLargeEnoughGap(minSize __generics_imported0.Addr) vmaGapIterator {
+	if n.maxGap.Get() < minSize {
+		return vmaGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := vmaGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap vmaGapIterator) NextGap() vmaGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap vmaGapIterator) NextLargeEnoughGap(minSize __generics_imported0.Addr) vmaGapIterator {
+	if vmatrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap vmaGapIterator) nextLargeEnoughGapHelper(minSize __generics_imported0.Addr) vmaGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return vmaGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap vmaGapIterator) PrevLargeEnoughGap(minSize __generics_imported0.Addr) vmaGapIterator {
+	if vmatrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap vmaGapIterator) prevLargeEnoughGapHelper(minSize __generics_imported0.Addr) vmaGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return vmaGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *vmanode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if vmatrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *vmaSet) ImportSortedSlices(sds *vmaSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *vmaSet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.AddrRange, vma) error) error {
+	havePrev := false
+	prev := __generics_imported0.Addr(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *vmaSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *vmaSet) saveRoot() *vmaSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/pgalloc/evictable_range.go b/pkg/sentry/pgalloc/evictable_range.go
index 10ce2ff44..10ce2ff44 100755..100644
--- a/pkg/sentry/pgalloc/evictable_range.go
+++ b/pkg/sentry/pgalloc/evictable_range.go
diff --git a/pkg/sentry/pgalloc/evictable_range_set.go b/pkg/sentry/pgalloc/evictable_range_set.go
index 6fbd02434..335446b4f 100755..100644
--- a/pkg/sentry/pgalloc/evictable_range_set.go
+++ b/pkg/sentry/pgalloc/evictable_range_set.go
@@ -5,6 +5,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const evictableRangetrackGaps = 0
+
+var _ = uint8(evictableRangetrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type evictableRangedynamicGap [evictableRangetrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *evictableRangedynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *evictableRangedynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -263,8 +291,12 @@ func (s *evictableRangeSet) Insert(gap evictableRangeGapIterator, r EvictableRan
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (evictableRangeSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := evictableRangetrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (evictableRangeSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -278,11 +310,16 @@ func (s *evictableRangeSet) Insert(gap evictableRangeGapIterator, r EvictableRan
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (evictableRangeSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := evictableRangetrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -309,11 +346,15 @@ func (s *evictableRangeSet) InsertWithoutMerging(gap evictableRangeGapIterator,
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *evictableRangeSet) InsertWithoutMergingUnchecked(gap evictableRangeGapIterator, r EvictableRange, val evictableRangeSetValue) evictableRangeIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := evictableRangetrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return evictableRangeIterator{gap.node, gap.index}
 }
 
@@ -328,12 +369,20 @@ func (s *evictableRangeSet) Remove(seg evictableRangeIterator) evictableRangeGap
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if evictableRangetrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	evictableRangeSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if evictableRangetrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(evictableRangeGapIterator{seg.node, seg.index})
 }
 
@@ -383,6 +432,7 @@ func (s *evictableRangeSet) MergeUnchecked(first, second evictableRangeIterator)
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -558,6 +608,12 @@ type evictableRangenode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap evictableRangedynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [evictableRangemaxDegree - 1]EvictableRange
@@ -603,12 +659,12 @@ func (n *evictableRangenode) nextSibling() *evictableRangenode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *evictableRangenode) rebalanceBeforeInsert(gap evictableRangeGapIterator) evictableRangeGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < evictableRangemaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &evictableRangenode{
@@ -644,6 +700,11 @@ func (n *evictableRangenode) rebalanceBeforeInsert(gap evictableRangeGapIterator
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if evictableRangetrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -681,6 +742,11 @@ func (n *evictableRangenode) rebalanceBeforeInsert(gap evictableRangeGapIterator
 	}
 	n.nrSegments = evictableRangeminDegree - 1
 
+	if evictableRangetrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -726,6 +792,11 @@ func (n *evictableRangenode) rebalanceAfterRemove(gap evictableRangeGapIterator)
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if evictableRangetrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return evictableRangeGapIterator{n, 0}
 			}
@@ -754,6 +825,11 @@ func (n *evictableRangenode) rebalanceAfterRemove(gap evictableRangeGapIterator)
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if evictableRangetrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return evictableRangeGapIterator{n, n.nrSegments}
@@ -786,6 +862,7 @@ func (n *evictableRangenode) rebalanceAfterRemove(gap evictableRangeGapIterator)
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return evictableRangeGapIterator{p, gap.index}
 			}
@@ -832,10 +909,146 @@ func (n *evictableRangenode) rebalanceAfterRemove(gap evictableRangeGapIterator)
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if evictableRangetrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *evictableRangenode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *evictableRangenode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *evictableRangenode) calculateMaxGapLeaf() uint64 {
+	max := evictableRangeGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (evictableRangeGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *evictableRangenode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *evictableRangenode) searchFirstLargeEnoughGap(minSize uint64) evictableRangeGapIterator {
+	if n.maxGap.Get() < minSize {
+		return evictableRangeGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := evictableRangeGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *evictableRangenode) searchLastLargeEnoughGap(minSize uint64) evictableRangeGapIterator {
+	if n.maxGap.Get() < minSize {
+		return evictableRangeGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := evictableRangeGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1141,6 +1354,114 @@ func (gap evictableRangeGapIterator) NextGap() evictableRangeGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap evictableRangeGapIterator) NextLargeEnoughGap(minSize uint64) evictableRangeGapIterator {
+	if evictableRangetrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap evictableRangeGapIterator) nextLargeEnoughGapHelper(minSize uint64) evictableRangeGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return evictableRangeGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap evictableRangeGapIterator) PrevLargeEnoughGap(minSize uint64) evictableRangeGapIterator {
+	if evictableRangetrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap evictableRangeGapIterator) prevLargeEnoughGapHelper(minSize uint64) evictableRangeGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return evictableRangeGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1207,7 +1528,15 @@ func (n *evictableRangenode) writeDebugString(buf *bytes.Buffer, prefix string)
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if evictableRangetrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1259,6 +1588,46 @@ func (s *evictableRangeSet) ImportSortedSlices(sds *evictableRangeSegmentDataSli
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *evictableRangeSet) segmentTestCheck(expectedSegments int, segFunc func(int, EvictableRange, evictableRangeSetValue) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *evictableRangeSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *evictableRangeSet) saveRoot() *evictableRangeSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/pgalloc/pgalloc_state_autogen.go b/pkg/sentry/pgalloc/pgalloc_state_autogen.go
index 97e1c883b..469630448 100755..100644
--- a/pkg/sentry/pgalloc/pgalloc_state_autogen.go
+++ b/pkg/sentry/pgalloc/pgalloc_state_autogen.go
@@ -38,6 +38,7 @@ func (x *evictableRangenode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -49,6 +50,7 @@ func (x *evictableRangenode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
@@ -103,6 +105,7 @@ func (x *usagenode) save(m state.Map) {
 	m.Save("parent", &x.parent)
 	m.Save("parentIndex", &x.parentIndex)
 	m.Save("hasChildren", &x.hasChildren)
+	m.Save("maxGap", &x.maxGap)
 	m.Save("keys", &x.keys)
 	m.Save("values", &x.values)
 	m.Save("children", &x.children)
@@ -114,6 +117,7 @@ func (x *usagenode) load(m state.Map) {
 	m.Load("parent", &x.parent)
 	m.Load("parentIndex", &x.parentIndex)
 	m.Load("hasChildren", &x.hasChildren)
+	m.Load("maxGap", &x.maxGap)
 	m.Load("keys", &x.keys)
 	m.Load("values", &x.values)
 	m.Load("children", &x.children)
diff --git a/pkg/sentry/pgalloc/pgalloc_unsafe_state_autogen.go b/pkg/sentry/pgalloc/pgalloc_unsafe_state_autogen.go
index 87c214008..87c214008 100755..100644
--- a/pkg/sentry/pgalloc/pgalloc_unsafe_state_autogen.go
+++ b/pkg/sentry/pgalloc/pgalloc_unsafe_state_autogen.go
diff --git a/pkg/sentry/pgalloc/usage_set.go b/pkg/sentry/pgalloc/usage_set.go
index 37b9235ca..79db792d9 100755..100644
--- a/pkg/sentry/pgalloc/usage_set.go
+++ b/pkg/sentry/pgalloc/usage_set.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const usagetrackGaps = 0
+
+var _ = uint8(usagetrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type usagedynamicGap [usagetrackGaps]uint64
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *usagedynamicGap) Get() uint64 {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *usagedynamicGap) Set(v uint64) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *usageSet) Insert(gap usageGapIterator, r __generics_imported0.FileRange
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (usageSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := usagetrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (usageSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *usageSet) Insert(gap usageGapIterator, r __generics_imported0.FileRange
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (usageSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := usagetrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *usageSet) InsertWithoutMerging(gap usageGapIterator, r __generics_impor
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *usageSet) InsertWithoutMergingUnchecked(gap usageGapIterator, r __generics_imported0.FileRange, val usageInfo) usageIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := usagetrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return usageIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *usageSet) Remove(seg usageIterator) usageGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if usagetrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	usageSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if usagetrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(usageGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *usageSet) MergeUnchecked(first, second usageIterator) usageIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type usagenode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap usagedynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [usagemaxDegree - 1]__generics_imported0.FileRange
@@ -607,12 +663,12 @@ func (n *usagenode) nextSibling() *usagenode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *usagenode) rebalanceBeforeInsert(gap usageGapIterator) usageGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < usagemaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &usagenode{
@@ -648,6 +704,11 @@ func (n *usagenode) rebalanceBeforeInsert(gap usageGapIterator) usageGapIterator
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if usagetrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *usagenode) rebalanceBeforeInsert(gap usageGapIterator) usageGapIterator
 	}
 	n.nrSegments = usageminDegree - 1
 
+	if usagetrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *usagenode) rebalanceAfterRemove(gap usageGapIterator) usageGapIterator
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if usagetrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return usageGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *usagenode) rebalanceAfterRemove(gap usageGapIterator) usageGapIterator
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if usagetrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return usageGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *usagenode) rebalanceAfterRemove(gap usageGapIterator) usageGapIterator
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return usageGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *usagenode) rebalanceAfterRemove(gap usageGapIterator) usageGapIterator
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if usagetrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *usagenode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *usagenode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *usagenode) calculateMaxGapLeaf() uint64 {
+	max := usageGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (usageGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *usagenode) calculateMaxGapInternal() uint64 {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *usagenode) searchFirstLargeEnoughGap(minSize uint64) usageGapIterator {
+	if n.maxGap.Get() < minSize {
+		return usageGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := usageGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *usagenode) searchLastLargeEnoughGap(minSize uint64) usageGapIterator {
+	if n.maxGap.Get() < minSize {
+		return usageGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := usageGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap usageGapIterator) NextGap() usageGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap usageGapIterator) NextLargeEnoughGap(minSize uint64) usageGapIterator {
+	if usagetrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap usageGapIterator) nextLargeEnoughGapHelper(minSize uint64) usageGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return usageGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap usageGapIterator) PrevLargeEnoughGap(minSize uint64) usageGapIterator {
+	if usagetrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap usageGapIterator) prevLargeEnoughGapHelper(minSize uint64) usageGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return usageGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *usagenode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if usagetrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *usageSet) ImportSortedSlices(sds *usageSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *usageSet) segmentTestCheck(expectedSegments int, segFunc func(int, __generics_imported0.FileRange, usageInfo) error) error {
+	havePrev := false
+	prev := uint64(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *usageSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *usageSet) saveRoot() *usageSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/sentry/platform/file_range.go b/pkg/sentry/platform/file_range.go
index 685d360e3..685d360e3 100755..100644
--- a/pkg/sentry/platform/file_range.go
+++ b/pkg/sentry/platform/file_range.go
diff --git a/pkg/sentry/platform/interrupt/interrupt_state_autogen.go b/pkg/sentry/platform/interrupt/interrupt_state_autogen.go
index 1336e5f01..1336e5f01 100755..100644
--- a/pkg/sentry/platform/interrupt/interrupt_state_autogen.go
+++ b/pkg/sentry/platform/interrupt/interrupt_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/bluepill_arm64.go b/pkg/sentry/platform/kvm/bluepill_arm64.go
index c215d443c..c215d443c 100755..100644
--- a/pkg/sentry/platform/kvm/bluepill_arm64.go
+++ b/pkg/sentry/platform/kvm/bluepill_arm64.go
diff --git a/pkg/sentry/platform/kvm/bluepill_arm64.s b/pkg/sentry/platform/kvm/bluepill_arm64.s
index 04efa0147..04efa0147 100755..100644
--- a/pkg/sentry/platform/kvm/bluepill_arm64.s
+++ b/pkg/sentry/platform/kvm/bluepill_arm64.s
diff --git a/pkg/sentry/platform/kvm/bluepill_arm64_unsafe.go b/pkg/sentry/platform/kvm/bluepill_arm64_unsafe.go
index 4ca2b7717..4ca2b7717 100755..100644
--- a/pkg/sentry/platform/kvm/bluepill_arm64_unsafe.go
+++ b/pkg/sentry/platform/kvm/bluepill_arm64_unsafe.go
diff --git a/pkg/sentry/platform/kvm/filters_amd64.go b/pkg/sentry/platform/kvm/filters_amd64.go
index 7d949f1dd..7d949f1dd 100755..100644
--- a/pkg/sentry/platform/kvm/filters_amd64.go
+++ b/pkg/sentry/platform/kvm/filters_amd64.go
diff --git a/pkg/sentry/platform/kvm/filters_arm64.go b/pkg/sentry/platform/kvm/filters_arm64.go
index 9245d07c2..9245d07c2 100755..100644
--- a/pkg/sentry/platform/kvm/filters_arm64.go
+++ b/pkg/sentry/platform/kvm/filters_arm64.go
diff --git a/pkg/sentry/platform/kvm/kvm_amd64_state_autogen.go b/pkg/sentry/platform/kvm/kvm_amd64_state_autogen.go
index a69cbee8b..a69cbee8b 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_amd64_state_autogen.go
+++ b/pkg/sentry/platform/kvm/kvm_amd64_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/kvm_amd64_unsafe_state_autogen.go b/pkg/sentry/platform/kvm/kvm_amd64_unsafe_state_autogen.go
index a69cbee8b..a69cbee8b 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_amd64_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/kvm/kvm_amd64_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/kvm_arm64.go b/pkg/sentry/platform/kvm/kvm_arm64.go
index 29d457a7e..29d457a7e 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_arm64.go
+++ b/pkg/sentry/platform/kvm/kvm_arm64.go
diff --git a/pkg/sentry/platform/kvm/kvm_arm64_state_autogen.go b/pkg/sentry/platform/kvm/kvm_arm64_state_autogen.go
index 90183b764..90183b764 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_arm64_state_autogen.go
+++ b/pkg/sentry/platform/kvm/kvm_arm64_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/kvm_arm64_unsafe.go b/pkg/sentry/platform/kvm/kvm_arm64_unsafe.go
index 6531bae1d..6531bae1d 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_arm64_unsafe.go
+++ b/pkg/sentry/platform/kvm/kvm_arm64_unsafe.go
diff --git a/pkg/sentry/platform/kvm/kvm_arm64_unsafe_state_autogen.go b/pkg/sentry/platform/kvm/kvm_arm64_unsafe_state_autogen.go
index 90183b764..90183b764 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_arm64_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/kvm/kvm_arm64_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/kvm_const_arm64.go b/pkg/sentry/platform/kvm/kvm_const_arm64.go
index 531ae8b1e..531ae8b1e 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_const_arm64.go
+++ b/pkg/sentry/platform/kvm/kvm_const_arm64.go
diff --git a/pkg/sentry/platform/kvm/kvm_state_autogen.go b/pkg/sentry/platform/kvm/kvm_state_autogen.go
index 8d85b96d0..8d85b96d0 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_state_autogen.go
+++ b/pkg/sentry/platform/kvm/kvm_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/kvm_unsafe_state_autogen.go b/pkg/sentry/platform/kvm/kvm_unsafe_state_autogen.go
index 2325262dc..2325262dc 100755..100644
--- a/pkg/sentry/platform/kvm/kvm_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/kvm/kvm_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/kvm/machine_arm64.go b/pkg/sentry/platform/kvm/machine_arm64.go
index e42505542..e42505542 100755..100644
--- a/pkg/sentry/platform/kvm/machine_arm64.go
+++ b/pkg/sentry/platform/kvm/machine_arm64.go
diff --git a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
index 3c02cef7c..3c02cef7c 100755..100644
--- a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
diff --git a/pkg/sentry/platform/kvm/physical_map_amd64.go b/pkg/sentry/platform/kvm/physical_map_amd64.go
index c5adfb577..c5adfb577 100755..100644
--- a/pkg/sentry/platform/kvm/physical_map_amd64.go
+++ b/pkg/sentry/platform/kvm/physical_map_amd64.go
diff --git a/pkg/sentry/platform/kvm/physical_map_arm64.go b/pkg/sentry/platform/kvm/physical_map_arm64.go
index 4d8561453..4d8561453 100755..100644
--- a/pkg/sentry/platform/kvm/physical_map_arm64.go
+++ b/pkg/sentry/platform/kvm/physical_map_arm64.go
diff --git a/pkg/sentry/platform/platform_state_autogen.go b/pkg/sentry/platform/platform_state_autogen.go
index 7597195ef..7597195ef 100755..100644
--- a/pkg/sentry/platform/platform_state_autogen.go
+++ b/pkg/sentry/platform/platform_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_amd64_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_amd64_state_autogen.go
index f730ab393..f730ab393 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_amd64_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_amd64_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_arm64_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_arm64_state_autogen.go
index 6239d1305..6239d1305 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_arm64_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_arm64_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe.go b/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe.go
index 32b8a6be9..32b8a6be9 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe.go
+++ b/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe_state_autogen.go
index 6239d1305..6239d1305 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_arm64_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_linux_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_linux_state_autogen.go
index 9f90aef93..9f90aef93 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_linux_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_linux_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_linux_unsafe_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_linux_unsafe_state_autogen.go
index 45d94c547..45d94c547 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_linux_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_linux_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_state_autogen.go
index 1bf0526f9..1bf0526f9 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_state_autogen.go
diff --git a/pkg/sentry/platform/ptrace/ptrace_unsafe_state_autogen.go b/pkg/sentry/platform/ptrace/ptrace_unsafe_state_autogen.go
index 4526fc387..4526fc387 100755..100644
--- a/pkg/sentry/platform/ptrace/ptrace_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/ptrace/ptrace_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/defs_impl_amd64.go b/pkg/sentry/platform/ring0/defs_impl_amd64.go
index 029d699fe..50ac3040e 100755..100644
--- a/pkg/sentry/platform/ring0/defs_impl_amd64.go
+++ b/pkg/sentry/platform/ring0/defs_impl_amd64.go
@@ -1,11 +1,11 @@
 package ring0
 
 import (
-	"gvisor.dev/gvisor/pkg/cpuid"
-	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/platform/ring0/pagetables"
 
 	"fmt"
+	"gvisor.dev/gvisor/pkg/cpuid"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/usermem"
 	"io"
 	"reflect"
diff --git a/pkg/sentry/platform/ring0/defs_impl_arm64.go b/pkg/sentry/platform/ring0/defs_impl_arm64.go
index 93f23047d..93f23047d 100755..100644
--- a/pkg/sentry/platform/ring0/defs_impl_arm64.go
+++ b/pkg/sentry/platform/ring0/defs_impl_arm64.go
diff --git a/pkg/sentry/platform/ring0/entry_arm64.go b/pkg/sentry/platform/ring0/entry_arm64.go
index 62a93f3d6..62a93f3d6 100755..100644
--- a/pkg/sentry/platform/ring0/entry_arm64.go
+++ b/pkg/sentry/platform/ring0/entry_arm64.go
diff --git a/pkg/sentry/platform/ring0/entry_impl_amd64.s b/pkg/sentry/platform/ring0/entry_impl_amd64.s
index daba45f9d..daba45f9d 100755..100644
--- a/pkg/sentry/platform/ring0/entry_impl_amd64.s
+++ b/pkg/sentry/platform/ring0/entry_impl_amd64.s
diff --git a/pkg/sentry/platform/ring0/entry_impl_arm64.s b/pkg/sentry/platform/ring0/entry_impl_arm64.s
index ea202219a..ea202219a 100755..100644
--- a/pkg/sentry/platform/ring0/entry_impl_arm64.s
+++ b/pkg/sentry/platform/ring0/entry_impl_arm64.s
diff --git a/pkg/sentry/platform/ring0/kernel_arm64.go b/pkg/sentry/platform/ring0/kernel_arm64.go
index ccacaea6b..ccacaea6b 100755..100644
--- a/pkg/sentry/platform/ring0/kernel_arm64.go
+++ b/pkg/sentry/platform/ring0/kernel_arm64.go
diff --git a/pkg/sentry/platform/ring0/lib_arm64.go b/pkg/sentry/platform/ring0/lib_arm64.go
index 444a83913..a6345010d 100755..100644
--- a/pkg/sentry/platform/ring0/lib_arm64.go
+++ b/pkg/sentry/platform/ring0/lib_arm64.go
@@ -38,6 +38,12 @@ func SaveVRegs(*byte)
 // LoadVRegs loads V0-V31 registers.
 func LoadVRegs(*byte)
 
+// GetTLS returns the value of TPIDR_EL0 register.
+func GetTLS() (value uint64)
+
+// SetTLS writes the TPIDR_EL0 value.
+func SetTLS(value uint64)
+
 // Init sets function pointers based on architectural features.
 //
 // This must be called prior to using ring0.
diff --git a/pkg/sentry/platform/ring0/lib_arm64.s b/pkg/sentry/platform/ring0/lib_arm64.s
index 0e6a6235b..b63e14b41 100755..100644
--- a/pkg/sentry/platform/ring0/lib_arm64.s
+++ b/pkg/sentry/platform/ring0/lib_arm64.s
@@ -15,6 +15,16 @@
 #include "funcdata.h"
 #include "textflag.h"
 
+TEXT ·GetTLS(SB),NOSPLIT,$0-8
+	MRS TPIDR_EL0, R1
+	MOVD R1, ret+0(FP)
+	RET
+
+TEXT ·SetTLS(SB),NOSPLIT,$0-8
+	MOVD addr+0(FP), R1
+	MSR R1, TPIDR_EL0
+	RET
+
 TEXT ·CPACREL1(SB),NOSPLIT,$0-8
 	WORD $0xd5381041 	// MRS CPACR_EL1, R1
 	MOVD R1, ret+0(FP)
diff --git a/pkg/sentry/platform/ring0/lib_arm64_unsafe.go b/pkg/sentry/platform/ring0/lib_arm64_unsafe.go
index c05166fea..c05166fea 100755..100644
--- a/pkg/sentry/platform/ring0/lib_arm64_unsafe.go
+++ b/pkg/sentry/platform/ring0/lib_arm64_unsafe.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64.go b/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64.go
index 78510ebed..78510ebed 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64_state_autogen.go b/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64_state_autogen.go
index a24523f87..a24523f87 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_aarch64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_amd64_state_autogen.go b/pkg/sentry/platform/ring0/pagetables/pagetables_amd64_state_autogen.go
index f48a8acd1..f48a8acd1 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_amd64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_amd64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_arm64.go b/pkg/sentry/platform/ring0/pagetables/pagetables_arm64.go
index 1a49f12a2..1a49f12a2 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_arm64.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_arm64.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_arm64_state_autogen.go b/pkg/sentry/platform/ring0/pagetables/pagetables_arm64_state_autogen.go
index ae9d2b272..ae9d2b272 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_arm64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_arm64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_state_autogen.go b/pkg/sentry/platform/ring0/pagetables/pagetables_state_autogen.go
index 4c4540603..4c4540603 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_state_autogen.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_unsafe_state_autogen.go b/pkg/sentry/platform/ring0/pagetables/pagetables_unsafe_state_autogen.go
index 4c4540603..4c4540603 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pagetables_x86_state_autogen.go b/pkg/sentry/platform/ring0/pagetables/pagetables_x86_state_autogen.go
index 6fe78c51c..6fe78c51c 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pagetables_x86_state_autogen.go
+++ b/pkg/sentry/platform/ring0/pagetables/pagetables_x86_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids.go b/pkg/sentry/platform/ring0/pagetables/pcids.go
index 964496aac..964496aac 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pcids.go
+++ b/pkg/sentry/platform/ring0/pagetables/pcids.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.go b/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.go
index fbfd41d83..fbfd41d83 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.go
+++ b/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.go
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.s b/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.s
index e9d62d768..e9d62d768 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.s
+++ b/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.s
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids_x86.go b/pkg/sentry/platform/ring0/pagetables/pcids_x86.go
index 91fc5e8dd..91fc5e8dd 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/pcids_x86.go
+++ b/pkg/sentry/platform/ring0/pagetables/pcids_x86.go
diff --git a/pkg/sentry/platform/ring0/pagetables/walker_amd64.go b/pkg/sentry/platform/ring0/pagetables/walker_amd64.go
index 8f9dacd93..8f9dacd93 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/walker_amd64.go
+++ b/pkg/sentry/platform/ring0/pagetables/walker_amd64.go
diff --git a/pkg/sentry/platform/ring0/pagetables/walker_arm64.go b/pkg/sentry/platform/ring0/pagetables/walker_arm64.go
index c261d393a..c261d393a 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/walker_arm64.go
+++ b/pkg/sentry/platform/ring0/pagetables/walker_arm64.go
diff --git a/pkg/sentry/platform/ring0/pagetables/walker_empty.go b/pkg/sentry/platform/ring0/pagetables/walker_empty.go
index 417784e17..417784e17 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/walker_empty.go
+++ b/pkg/sentry/platform/ring0/pagetables/walker_empty.go
diff --git a/pkg/sentry/platform/ring0/pagetables/walker_lookup.go b/pkg/sentry/platform/ring0/pagetables/walker_lookup.go
index 906c9c50f..906c9c50f 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/walker_lookup.go
+++ b/pkg/sentry/platform/ring0/pagetables/walker_lookup.go
diff --git a/pkg/sentry/platform/ring0/pagetables/walker_map.go b/pkg/sentry/platform/ring0/pagetables/walker_map.go
index 61ee3c825..61ee3c825 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/walker_map.go
+++ b/pkg/sentry/platform/ring0/pagetables/walker_map.go
diff --git a/pkg/sentry/platform/ring0/pagetables/walker_unmap.go b/pkg/sentry/platform/ring0/pagetables/walker_unmap.go
index be2aa0ce4..be2aa0ce4 100755..100644
--- a/pkg/sentry/platform/ring0/pagetables/walker_unmap.go
+++ b/pkg/sentry/platform/ring0/pagetables/walker_unmap.go
diff --git a/pkg/sentry/platform/ring0/ring0_amd64_state_autogen.go b/pkg/sentry/platform/ring0/ring0_amd64_state_autogen.go
index 96cf5d331..96cf5d331 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_amd64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_amd64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/ring0_arm64_state_autogen.go b/pkg/sentry/platform/ring0/ring0_arm64_state_autogen.go
index 7f2ab3537..7f2ab3537 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_arm64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_arm64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/ring0_arm64_unsafe_state_autogen.go b/pkg/sentry/platform/ring0/ring0_arm64_unsafe_state_autogen.go
index fa617c57e..fa617c57e 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_arm64_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_arm64_unsafe_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/ring0_impl_amd64_state_autogen.go b/pkg/sentry/platform/ring0/ring0_impl_amd64_state_autogen.go
index 327aba163..327aba163 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_impl_amd64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_impl_amd64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/ring0_impl_arm64_state_autogen.go b/pkg/sentry/platform/ring0/ring0_impl_arm64_state_autogen.go
index 327aba163..327aba163 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_impl_arm64_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_impl_arm64_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/ring0_state_autogen.go b/pkg/sentry/platform/ring0/ring0_state_autogen.go
index 327aba163..327aba163 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_state_autogen.go
diff --git a/pkg/sentry/platform/ring0/ring0_unsafe_state_autogen.go b/pkg/sentry/platform/ring0/ring0_unsafe_state_autogen.go
index 327aba163..327aba163 100755..100644
--- a/pkg/sentry/platform/ring0/ring0_unsafe_state_autogen.go
+++ b/pkg/sentry/platform/ring0/ring0_unsafe_state_autogen.go
diff --git a/pkg/sentry/sighandling/sighandling_state_autogen.go b/pkg/sentry/sighandling/sighandling_state_autogen.go
index da9d96382..da9d96382 100755..100644
--- a/pkg/sentry/sighandling/sighandling_state_autogen.go
+++ b/pkg/sentry/sighandling/sighandling_state_autogen.go
diff --git a/pkg/sentry/sighandling/sighandling_unsafe_state_autogen.go b/pkg/sentry/sighandling/sighandling_unsafe_state_autogen.go
index da9d96382..da9d96382 100755..100644
--- a/pkg/sentry/sighandling/sighandling_unsafe_state_autogen.go
+++ b/pkg/sentry/sighandling/sighandling_unsafe_state_autogen.go
diff --git a/pkg/sentry/socket/control/control_state_autogen.go b/pkg/sentry/socket/control/control_state_autogen.go
index 8a37b04c0..8a37b04c0 100755..100644
--- a/pkg/sentry/socket/control/control_state_autogen.go
+++ b/pkg/sentry/socket/control/control_state_autogen.go
diff --git a/pkg/sentry/socket/control/control_vfs2.go b/pkg/sentry/socket/control/control_vfs2.go
index fd08179be..fd08179be 100755..100644
--- a/pkg/sentry/socket/control/control_vfs2.go
+++ b/pkg/sentry/socket/control/control_vfs2.go
diff --git a/pkg/sentry/socket/hostinet/hostinet_impl_state_autogen.go b/pkg/sentry/socket/hostinet/hostinet_impl_state_autogen.go
index b0a59ba93..b0a59ba93 100755..100644
--- a/pkg/sentry/socket/hostinet/hostinet_impl_state_autogen.go
+++ b/pkg/sentry/socket/hostinet/hostinet_impl_state_autogen.go
diff --git a/pkg/sentry/socket/hostinet/hostinet_state_autogen.go b/pkg/sentry/socket/hostinet/hostinet_state_autogen.go
index 333811074..333811074 100755..100644
--- a/pkg/sentry/socket/hostinet/hostinet_state_autogen.go
+++ b/pkg/sentry/socket/hostinet/hostinet_state_autogen.go
diff --git a/pkg/sentry/socket/hostinet/hostinet_unsafe_state_autogen.go b/pkg/sentry/socket/hostinet/hostinet_unsafe_state_autogen.go
index b0a59ba93..b0a59ba93 100755..100644
--- a/pkg/sentry/socket/hostinet/hostinet_unsafe_state_autogen.go
+++ b/pkg/sentry/socket/hostinet/hostinet_unsafe_state_autogen.go
diff --git a/pkg/sentry/socket/hostinet/socket.go b/pkg/sentry/socket/hostinet/socket.go
index b49433326..c11e82c10 100644
--- a/pkg/sentry/socket/hostinet/socket.go
+++ b/pkg/sentry/socket/hostinet/socket.go
@@ -555,7 +555,7 @@ func (s *socketOpsCommon) SendMsg(t *kernel.Task, src usermem.IOSequence, to []b
 		if uint64(src.NumBytes()) != srcs.NumBytes() {
 			return 0, nil
 		}
-		if srcs.IsEmpty() {
+		if srcs.IsEmpty() && len(controlBuf) == 0 {
 			return 0, nil
 		}
 
diff --git a/pkg/sentry/socket/hostinet/socket_vfs2.go b/pkg/sentry/socket/hostinet/socket_vfs2.go
index 677743113..677743113 100755..100644
--- a/pkg/sentry/socket/hostinet/socket_vfs2.go
+++ b/pkg/sentry/socket/hostinet/socket_vfs2.go
diff --git a/pkg/sentry/socket/hostinet/sockopt_impl.go b/pkg/sentry/socket/hostinet/sockopt_impl.go
index 8a783712e..8a783712e 100755..100644
--- a/pkg/sentry/socket/hostinet/sockopt_impl.go
+++ b/pkg/sentry/socket/hostinet/sockopt_impl.go
diff --git a/pkg/sentry/socket/netfilter/extensions.go b/pkg/sentry/socket/netfilter/extensions.go
index 0336a32d8..0336a32d8 100755..100644
--- a/pkg/sentry/socket/netfilter/extensions.go
+++ b/pkg/sentry/socket/netfilter/extensions.go
diff --git a/pkg/sentry/socket/netfilter/netfilter_state_autogen.go b/pkg/sentry/socket/netfilter/netfilter_state_autogen.go
index 6e95d89a4..6e95d89a4 100755..100644
--- a/pkg/sentry/socket/netfilter/netfilter_state_autogen.go
+++ b/pkg/sentry/socket/netfilter/netfilter_state_autogen.go
diff --git a/pkg/sentry/socket/netfilter/owner_matcher.go b/pkg/sentry/socket/netfilter/owner_matcher.go
index 3863293c7..3863293c7 100755..100644
--- a/pkg/sentry/socket/netfilter/owner_matcher.go
+++ b/pkg/sentry/socket/netfilter/owner_matcher.go
diff --git a/pkg/sentry/socket/netfilter/targets.go b/pkg/sentry/socket/netfilter/targets.go
index 84abe8d29..84abe8d29 100755..100644
--- a/pkg/sentry/socket/netfilter/targets.go
+++ b/pkg/sentry/socket/netfilter/targets.go
diff --git a/pkg/sentry/socket/netfilter/tcp_matcher.go b/pkg/sentry/socket/netfilter/tcp_matcher.go
index 57a1e1c12..57a1e1c12 100755..100644
--- a/pkg/sentry/socket/netfilter/tcp_matcher.go
+++ b/pkg/sentry/socket/netfilter/tcp_matcher.go
diff --git a/pkg/sentry/socket/netfilter/udp_matcher.go b/pkg/sentry/socket/netfilter/udp_matcher.go
index cfa9e621d..cfa9e621d 100755..100644
--- a/pkg/sentry/socket/netfilter/udp_matcher.go
+++ b/pkg/sentry/socket/netfilter/udp_matcher.go
diff --git a/pkg/sentry/socket/netlink/netlink_state_autogen.go b/pkg/sentry/socket/netlink/netlink_state_autogen.go
index fa6a7ce74..fa6a7ce74 100755..100644
--- a/pkg/sentry/socket/netlink/netlink_state_autogen.go
+++ b/pkg/sentry/socket/netlink/netlink_state_autogen.go
diff --git a/pkg/sentry/socket/netlink/port/port_state_autogen.go b/pkg/sentry/socket/netlink/port/port_state_autogen.go
index c509cc7d5..c509cc7d5 100755..100644
--- a/pkg/sentry/socket/netlink/port/port_state_autogen.go
+++ b/pkg/sentry/socket/netlink/port/port_state_autogen.go
diff --git a/pkg/sentry/socket/netlink/provider_vfs2.go b/pkg/sentry/socket/netlink/provider_vfs2.go
index bb205be0d..bb205be0d 100755..100644
--- a/pkg/sentry/socket/netlink/provider_vfs2.go
+++ b/pkg/sentry/socket/netlink/provider_vfs2.go
diff --git a/pkg/sentry/socket/netlink/route/route_state_autogen.go b/pkg/sentry/socket/netlink/route/route_state_autogen.go
index bd10fe189..bd10fe189 100755..100644
--- a/pkg/sentry/socket/netlink/route/route_state_autogen.go
+++ b/pkg/sentry/socket/netlink/route/route_state_autogen.go
diff --git a/pkg/sentry/socket/netlink/socket_vfs2.go b/pkg/sentry/socket/netlink/socket_vfs2.go
index b854bf990..b854bf990 100755..100644
--- a/pkg/sentry/socket/netlink/socket_vfs2.go
+++ b/pkg/sentry/socket/netlink/socket_vfs2.go
diff --git a/pkg/sentry/socket/netlink/uevent/protocol.go b/pkg/sentry/socket/netlink/uevent/protocol.go
index 029ba21b5..029ba21b5 100755..100644
--- a/pkg/sentry/socket/netlink/uevent/protocol.go
+++ b/pkg/sentry/socket/netlink/uevent/protocol.go
diff --git a/pkg/sentry/socket/netlink/uevent/uevent_state_autogen.go b/pkg/sentry/socket/netlink/uevent/uevent_state_autogen.go
index b82dddf32..b82dddf32 100755..100644
--- a/pkg/sentry/socket/netlink/uevent/uevent_state_autogen.go
+++ b/pkg/sentry/socket/netlink/uevent/uevent_state_autogen.go
diff --git a/pkg/sentry/socket/netstack/device.go b/pkg/sentry/socket/netstack/device.go
index fbeb89fb8..fbeb89fb8 100755..100644
--- a/pkg/sentry/socket/netstack/device.go
+++ b/pkg/sentry/socket/netstack/device.go
diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index 60df51dae..60df51dae 100755..100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
diff --git a/pkg/sentry/socket/netstack/netstack_state_autogen.go b/pkg/sentry/socket/netstack/netstack_state_autogen.go
index a1f61607f..a1f61607f 100755..100644
--- a/pkg/sentry/socket/netstack/netstack_state_autogen.go
+++ b/pkg/sentry/socket/netstack/netstack_state_autogen.go
diff --git a/pkg/sentry/socket/netstack/netstack_vfs2.go b/pkg/sentry/socket/netstack/netstack_vfs2.go
index fcd8013c0..fcd8013c0 100755..100644
--- a/pkg/sentry/socket/netstack/netstack_vfs2.go
+++ b/pkg/sentry/socket/netstack/netstack_vfs2.go
diff --git a/pkg/sentry/socket/netstack/provider.go b/pkg/sentry/socket/netstack/provider.go
index ead3b2b79..ead3b2b79 100755..100644
--- a/pkg/sentry/socket/netstack/provider.go
+++ b/pkg/sentry/socket/netstack/provider.go
diff --git a/pkg/sentry/socket/netstack/provider_vfs2.go b/pkg/sentry/socket/netstack/provider_vfs2.go
index 2a01143f6..2a01143f6 100755..100644
--- a/pkg/sentry/socket/netstack/provider_vfs2.go
+++ b/pkg/sentry/socket/netstack/provider_vfs2.go
diff --git a/pkg/sentry/socket/netstack/save_restore.go b/pkg/sentry/socket/netstack/save_restore.go
index c7aaf722a..c7aaf722a 100755..100644
--- a/pkg/sentry/socket/netstack/save_restore.go
+++ b/pkg/sentry/socket/netstack/save_restore.go
diff --git a/pkg/sentry/socket/netstack/stack.go b/pkg/sentry/socket/netstack/stack.go
index f5fa18136..f5fa18136 100755..100644
--- a/pkg/sentry/socket/netstack/stack.go
+++ b/pkg/sentry/socket/netstack/stack.go
diff --git a/pkg/sentry/socket/socket_state_autogen.go b/pkg/sentry/socket/socket_state_autogen.go
index 900c217c7..900c217c7 100755..100644
--- a/pkg/sentry/socket/socket_state_autogen.go
+++ b/pkg/sentry/socket/socket_state_autogen.go
diff --git a/pkg/sentry/socket/unix/transport/transport_message_list.go b/pkg/sentry/socket/unix/transport/transport_message_list.go
index 568cd5871..568cd5871 100755..100644
--- a/pkg/sentry/socket/unix/transport/transport_message_list.go
+++ b/pkg/sentry/socket/unix/transport/transport_message_list.go
diff --git a/pkg/sentry/socket/unix/transport/transport_state_autogen.go b/pkg/sentry/socket/unix/transport/transport_state_autogen.go
index b47951498..b47951498 100755..100644
--- a/pkg/sentry/socket/unix/transport/transport_state_autogen.go
+++ b/pkg/sentry/socket/unix/transport/transport_state_autogen.go
diff --git a/pkg/sentry/socket/unix/unix_state_autogen.go b/pkg/sentry/socket/unix/unix_state_autogen.go
index aa05e7b99..aa05e7b99 100755..100644
--- a/pkg/sentry/socket/unix/unix_state_autogen.go
+++ b/pkg/sentry/socket/unix/unix_state_autogen.go
diff --git a/pkg/sentry/socket/unix/unix_vfs2.go b/pkg/sentry/socket/unix/unix_vfs2.go
index 45e109361..45e109361 100755..100644
--- a/pkg/sentry/socket/unix/unix_vfs2.go
+++ b/pkg/sentry/socket/unix/unix_vfs2.go
diff --git a/pkg/sentry/state/state_state_autogen.go b/pkg/sentry/state/state_state_autogen.go
index 6c2b29632..6c2b29632 100755..100644
--- a/pkg/sentry/state/state_state_autogen.go
+++ b/pkg/sentry/state/state_state_autogen.go
diff --git a/pkg/sentry/state/state_unsafe_state_autogen.go b/pkg/sentry/state/state_unsafe_state_autogen.go
index 6c2b29632..6c2b29632 100755..100644
--- a/pkg/sentry/state/state_unsafe_state_autogen.go
+++ b/pkg/sentry/state/state_unsafe_state_autogen.go
diff --git a/pkg/sentry/strace/epoll.go b/pkg/sentry/strace/epoll.go
index a6e48b836..a6e48b836 100755..100644
--- a/pkg/sentry/strace/epoll.go
+++ b/pkg/sentry/strace/epoll.go
diff --git a/pkg/sentry/strace/linux64_amd64.go b/pkg/sentry/strace/linux64_amd64.go
index 71b92eaee..71b92eaee 100755..100644
--- a/pkg/sentry/strace/linux64_amd64.go
+++ b/pkg/sentry/strace/linux64_amd64.go
diff --git a/pkg/sentry/strace/linux64_arm64.go b/pkg/sentry/strace/linux64_arm64.go
index bd7361a52..bd7361a52 100755..100644
--- a/pkg/sentry/strace/linux64_arm64.go
+++ b/pkg/sentry/strace/linux64_arm64.go
diff --git a/pkg/sentry/strace/select.go b/pkg/sentry/strace/select.go
index 3a4c32aa0..3a4c32aa0 100755..100644
--- a/pkg/sentry/strace/select.go
+++ b/pkg/sentry/strace/select.go
diff --git a/pkg/sentry/strace/strace_amd64_state_autogen.go b/pkg/sentry/strace/strace_amd64_state_autogen.go
index c7d4b3eb4..c7d4b3eb4 100755..100644
--- a/pkg/sentry/strace/strace_amd64_state_autogen.go
+++ b/pkg/sentry/strace/strace_amd64_state_autogen.go
diff --git a/pkg/sentry/strace/strace_arm64_state_autogen.go b/pkg/sentry/strace/strace_arm64_state_autogen.go
index 9b8f66dc9..9b8f66dc9 100755..100644
--- a/pkg/sentry/strace/strace_arm64_state_autogen.go
+++ b/pkg/sentry/strace/strace_arm64_state_autogen.go
diff --git a/pkg/sentry/strace/strace_go_proto/strace.pb.go b/pkg/sentry/strace/strace_go_proto/strace.pb.go
index ef45661bc..ef45661bc 100755..100644
--- a/pkg/sentry/strace/strace_go_proto/strace.pb.go
+++ b/pkg/sentry/strace/strace_go_proto/strace.pb.go
diff --git a/pkg/sentry/strace/strace_state_autogen.go b/pkg/sentry/strace/strace_state_autogen.go
index 33f6a7a54..33f6a7a54 100755..100644
--- a/pkg/sentry/strace/strace_state_autogen.go
+++ b/pkg/sentry/strace/strace_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/linux_amd64_state_autogen.go b/pkg/sentry/syscalls/linux/linux_amd64_state_autogen.go
index b3e3be0b6..b3e3be0b6 100755..100644
--- a/pkg/sentry/syscalls/linux/linux_amd64_state_autogen.go
+++ b/pkg/sentry/syscalls/linux/linux_amd64_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/linux_arm64_state_autogen.go b/pkg/sentry/syscalls/linux/linux_arm64_state_autogen.go
index f03e36ddc..f03e36ddc 100755..100644
--- a/pkg/sentry/syscalls/linux/linux_arm64_state_autogen.go
+++ b/pkg/sentry/syscalls/linux/linux_arm64_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/linux_state_autogen.go b/pkg/sentry/syscalls/linux/linux_state_autogen.go
index cbae0a871..cbae0a871 100755..100644
--- a/pkg/sentry/syscalls/linux/linux_state_autogen.go
+++ b/pkg/sentry/syscalls/linux/linux_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/sys_clone_amd64.go b/pkg/sentry/syscalls/linux/sys_clone_amd64.go
index dd43cf18d..dd43cf18d 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_clone_amd64.go
+++ b/pkg/sentry/syscalls/linux/sys_clone_amd64.go
diff --git a/pkg/sentry/syscalls/linux/sys_clone_arm64.go b/pkg/sentry/syscalls/linux/sys_clone_arm64.go
index cf68a8949..cf68a8949 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_clone_arm64.go
+++ b/pkg/sentry/syscalls/linux/sys_clone_arm64.go
diff --git a/pkg/sentry/syscalls/linux/sys_rseq.go b/pkg/sentry/syscalls/linux/sys_rseq.go
index 90db10ea6..90db10ea6 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_rseq.go
+++ b/pkg/sentry/syscalls/linux/sys_rseq.go
diff --git a/pkg/sentry/syscalls/linux/sys_stat_amd64.go b/pkg/sentry/syscalls/linux/sys_stat_amd64.go
index 0a04a6113..0a04a6113 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_stat_amd64.go
+++ b/pkg/sentry/syscalls/linux/sys_stat_amd64.go
diff --git a/pkg/sentry/syscalls/linux/sys_stat_arm64.go b/pkg/sentry/syscalls/linux/sys_stat_arm64.go
index 5a3b1bfad..5a3b1bfad 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_stat_arm64.go
+++ b/pkg/sentry/syscalls/linux/sys_stat_arm64.go
diff --git a/pkg/sentry/syscalls/linux/sys_tls_amd64.go b/pkg/sentry/syscalls/linux/sys_tls_amd64.go
index b3eb96a1c..b3eb96a1c 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_tls_amd64.go
+++ b/pkg/sentry/syscalls/linux/sys_tls_amd64.go
diff --git a/pkg/sentry/syscalls/linux/sys_tls_arm64.go b/pkg/sentry/syscalls/linux/sys_tls_arm64.go
index fb08a356e..fb08a356e 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_tls_arm64.go
+++ b/pkg/sentry/syscalls/linux/sys_tls_arm64.go
diff --git a/pkg/sentry/syscalls/linux/sys_xattr.go b/pkg/sentry/syscalls/linux/sys_xattr.go
index 2de5e3422..2de5e3422 100755..100644
--- a/pkg/sentry/syscalls/linux/sys_xattr.go
+++ b/pkg/sentry/syscalls/linux/sys_xattr.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/epoll.go b/pkg/sentry/syscalls/linux/vfs2/epoll.go
index 34c90ae3e..34c90ae3e 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/epoll.go
+++ b/pkg/sentry/syscalls/linux/vfs2/epoll.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/eventfd.go b/pkg/sentry/syscalls/linux/vfs2/eventfd.go
index aff1a2070..aff1a2070 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/eventfd.go
+++ b/pkg/sentry/syscalls/linux/vfs2/eventfd.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/execve.go b/pkg/sentry/syscalls/linux/vfs2/execve.go
index aef0078a8..aef0078a8 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/execve.go
+++ b/pkg/sentry/syscalls/linux/vfs2/execve.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/fd.go b/pkg/sentry/syscalls/linux/vfs2/fd.go
index ca0f7fd1e..ca0f7fd1e 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/fd.go
+++ b/pkg/sentry/syscalls/linux/vfs2/fd.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/filesystem.go b/pkg/sentry/syscalls/linux/vfs2/filesystem.go
index 46d3e189c..46d3e189c 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/filesystem.go
+++ b/pkg/sentry/syscalls/linux/vfs2/filesystem.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/fscontext.go b/pkg/sentry/syscalls/linux/vfs2/fscontext.go
index 317409a18..317409a18 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/fscontext.go
+++ b/pkg/sentry/syscalls/linux/vfs2/fscontext.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/getdents.go b/pkg/sentry/syscalls/linux/vfs2/getdents.go
index c7c7bf7ce..c7c7bf7ce 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/getdents.go
+++ b/pkg/sentry/syscalls/linux/vfs2/getdents.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/ioctl.go b/pkg/sentry/syscalls/linux/vfs2/ioctl.go
index 5a2418da9..5a2418da9 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/ioctl.go
+++ b/pkg/sentry/syscalls/linux/vfs2/ioctl.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/memfd.go b/pkg/sentry/syscalls/linux/vfs2/memfd.go
index bbe248d17..bbe248d17 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/memfd.go
+++ b/pkg/sentry/syscalls/linux/vfs2/memfd.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/mmap.go b/pkg/sentry/syscalls/linux/vfs2/mmap.go
index 60a43f0a0..60a43f0a0 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/mmap.go
+++ b/pkg/sentry/syscalls/linux/vfs2/mmap.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/path.go b/pkg/sentry/syscalls/linux/vfs2/path.go
index 97da6c647..97da6c647 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/path.go
+++ b/pkg/sentry/syscalls/linux/vfs2/path.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/pipe.go b/pkg/sentry/syscalls/linux/vfs2/pipe.go
index 4a01e4209..4a01e4209 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/pipe.go
+++ b/pkg/sentry/syscalls/linux/vfs2/pipe.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/poll.go b/pkg/sentry/syscalls/linux/vfs2/poll.go
index ff1b25d7b..ff1b25d7b 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/poll.go
+++ b/pkg/sentry/syscalls/linux/vfs2/poll.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/read_write.go b/pkg/sentry/syscalls/linux/vfs2/read_write.go
index 3a7ef24f5..3a7ef24f5 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/read_write.go
+++ b/pkg/sentry/syscalls/linux/vfs2/read_write.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/setstat.go b/pkg/sentry/syscalls/linux/vfs2/setstat.go
index 09ecfed26..09ecfed26 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/setstat.go
+++ b/pkg/sentry/syscalls/linux/vfs2/setstat.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/signal.go b/pkg/sentry/syscalls/linux/vfs2/signal.go
index 623992f6f..623992f6f 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/signal.go
+++ b/pkg/sentry/syscalls/linux/vfs2/signal.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/socket.go b/pkg/sentry/syscalls/linux/vfs2/socket.go
index 10b668477..10b668477 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/socket.go
+++ b/pkg/sentry/syscalls/linux/vfs2/socket.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/splice.go b/pkg/sentry/syscalls/linux/vfs2/splice.go
new file mode 100644
index 000000000..8f3c22a02
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/vfs2/splice.go
@@ -0,0 +1,286 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vfs2
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/pipe"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// Splice implements Linux syscall splice(2).
+func Splice(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	inFD := args[0].Int()
+	inOffsetPtr := args[1].Pointer()
+	outFD := args[2].Int()
+	outOffsetPtr := args[3].Pointer()
+	count := int64(args[4].SizeT())
+	flags := args[5].Int()
+
+	if count == 0 {
+		return 0, nil, nil
+	}
+	if count > int64(kernel.MAX_RW_COUNT) {
+		count = int64(kernel.MAX_RW_COUNT)
+	}
+
+	// Check for invalid flags.
+	if flags&^(linux.SPLICE_F_MOVE|linux.SPLICE_F_NONBLOCK|linux.SPLICE_F_MORE|linux.SPLICE_F_GIFT) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Get file descriptions.
+	inFile := t.GetFileVFS2(inFD)
+	if inFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer inFile.DecRef()
+	outFile := t.GetFileVFS2(outFD)
+	if outFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer outFile.DecRef()
+
+	// Check that both files support the required directionality.
+	if !inFile.IsReadable() || !outFile.IsWritable() {
+		return 0, nil, syserror.EBADF
+	}
+
+	// The operation is non-blocking if anything is non-blocking.
+	//
+	// N.B. This is a rather simplistic heuristic that avoids some
+	// poor edge case behavior since the exact semantics here are
+	// underspecified and vary between versions of Linux itself.
+	nonBlock := ((inFile.StatusFlags()|outFile.StatusFlags())&linux.O_NONBLOCK != 0) || (flags&linux.SPLICE_F_NONBLOCK != 0)
+
+	// At least one file description must represent a pipe.
+	inPipeFD, inIsPipe := inFile.Impl().(*pipe.VFSPipeFD)
+	outPipeFD, outIsPipe := outFile.Impl().(*pipe.VFSPipeFD)
+	if !inIsPipe && !outIsPipe {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Copy in offsets.
+	inOffset := int64(-1)
+	if inOffsetPtr != 0 {
+		if inIsPipe {
+			return 0, nil, syserror.ESPIPE
+		}
+		if inFile.Options().DenyPRead {
+			return 0, nil, syserror.EINVAL
+		}
+		if _, err := t.CopyIn(inOffsetPtr, &inOffset); err != nil {
+			return 0, nil, err
+		}
+		if inOffset < 0 {
+			return 0, nil, syserror.EINVAL
+		}
+	}
+	outOffset := int64(-1)
+	if outOffsetPtr != 0 {
+		if outIsPipe {
+			return 0, nil, syserror.ESPIPE
+		}
+		if outFile.Options().DenyPWrite {
+			return 0, nil, syserror.EINVAL
+		}
+		if _, err := t.CopyIn(outOffsetPtr, &outOffset); err != nil {
+			return 0, nil, err
+		}
+		if outOffset < 0 {
+			return 0, nil, syserror.EINVAL
+		}
+	}
+
+	// Move data.
+	var (
+		n     int64
+		err   error
+		inCh  chan struct{}
+		outCh chan struct{}
+	)
+	for {
+		// If both input and output are pipes, delegate to the pipe
+		// implementation. Otherwise, exactly one end is a pipe, which we
+		// ensure is consistently ordered after the non-pipe FD's locks by
+		// passing the pipe FD as usermem.IO to the non-pipe end.
+		switch {
+		case inIsPipe && outIsPipe:
+			n, err = pipe.Splice(t, outPipeFD, inPipeFD, count)
+		case inIsPipe:
+			if outOffset != -1 {
+				n, err = outFile.PWrite(t, inPipeFD.IOSequence(count), outOffset, vfs.WriteOptions{})
+				outOffset += n
+			} else {
+				n, err = outFile.Write(t, inPipeFD.IOSequence(count), vfs.WriteOptions{})
+			}
+		case outIsPipe:
+			if inOffset != -1 {
+				n, err = inFile.PRead(t, outPipeFD.IOSequence(count), inOffset, vfs.ReadOptions{})
+				inOffset += n
+			} else {
+				n, err = inFile.Read(t, outPipeFD.IOSequence(count), vfs.ReadOptions{})
+			}
+		}
+		if n != 0 || err != syserror.ErrWouldBlock || nonBlock {
+			break
+		}
+
+		// Note that the blocking behavior here is a bit different than the
+		// normal pattern. Because we need to have both data to read and data
+		// to write simultaneously, we actually explicitly block on both of
+		// these cases in turn before returning to the splice operation.
+		if inFile.Readiness(eventMaskRead)&eventMaskRead == 0 {
+			if inCh == nil {
+				inCh = make(chan struct{}, 1)
+				inW, _ := waiter.NewChannelEntry(inCh)
+				inFile.EventRegister(&inW, eventMaskRead)
+				defer inFile.EventUnregister(&inW)
+				continue // Need to refresh readiness.
+			}
+			if err = t.Block(inCh); err != nil {
+				break
+			}
+		}
+		if outFile.Readiness(eventMaskWrite)&eventMaskWrite == 0 {
+			if outCh == nil {
+				outCh = make(chan struct{}, 1)
+				outW, _ := waiter.NewChannelEntry(outCh)
+				outFile.EventRegister(&outW, eventMaskWrite)
+				defer outFile.EventUnregister(&outW)
+				continue // Need to refresh readiness.
+			}
+			if err = t.Block(outCh); err != nil {
+				break
+			}
+		}
+	}
+
+	// Copy updated offsets out.
+	if inOffsetPtr != 0 {
+		if _, err := t.CopyOut(inOffsetPtr, &inOffset); err != nil {
+			return 0, nil, err
+		}
+	}
+	if outOffsetPtr != 0 {
+		if _, err := t.CopyOut(outOffsetPtr, &outOffset); err != nil {
+			return 0, nil, err
+		}
+	}
+
+	if n == 0 {
+		return 0, nil, err
+	}
+	return uintptr(n), nil, nil
+}
+
+// Tee implements Linux syscall tee(2).
+func Tee(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	inFD := args[0].Int()
+	outFD := args[1].Int()
+	count := int64(args[2].SizeT())
+	flags := args[3].Int()
+
+	if count == 0 {
+		return 0, nil, nil
+	}
+	if count > int64(kernel.MAX_RW_COUNT) {
+		count = int64(kernel.MAX_RW_COUNT)
+	}
+
+	// Check for invalid flags.
+	if flags&^(linux.SPLICE_F_MOVE|linux.SPLICE_F_NONBLOCK|linux.SPLICE_F_MORE|linux.SPLICE_F_GIFT) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Get file descriptions.
+	inFile := t.GetFileVFS2(inFD)
+	if inFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer inFile.DecRef()
+	outFile := t.GetFileVFS2(outFD)
+	if outFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer outFile.DecRef()
+
+	// Check that both files support the required directionality.
+	if !inFile.IsReadable() || !outFile.IsWritable() {
+		return 0, nil, syserror.EBADF
+	}
+
+	// The operation is non-blocking if anything is non-blocking.
+	//
+	// N.B. This is a rather simplistic heuristic that avoids some
+	// poor edge case behavior since the exact semantics here are
+	// underspecified and vary between versions of Linux itself.
+	nonBlock := ((inFile.StatusFlags()|outFile.StatusFlags())&linux.O_NONBLOCK != 0) || (flags&linux.SPLICE_F_NONBLOCK != 0)
+
+	// Both file descriptions must represent pipes.
+	inPipeFD, inIsPipe := inFile.Impl().(*pipe.VFSPipeFD)
+	outPipeFD, outIsPipe := outFile.Impl().(*pipe.VFSPipeFD)
+	if !inIsPipe || !outIsPipe {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Copy data.
+	var (
+		inCh  chan struct{}
+		outCh chan struct{}
+	)
+	for {
+		n, err := pipe.Tee(t, outPipeFD, inPipeFD, count)
+		if n != 0 {
+			return uintptr(n), nil, nil
+		}
+		if err != syserror.ErrWouldBlock || nonBlock {
+			return 0, nil, err
+		}
+
+		// Note that the blocking behavior here is a bit different than the
+		// normal pattern. Because we need to have both data to read and data
+		// to write simultaneously, we actually explicitly block on both of
+		// these cases in turn before returning to the tee operation.
+		if inFile.Readiness(eventMaskRead)&eventMaskRead == 0 {
+			if inCh == nil {
+				inCh = make(chan struct{}, 1)
+				inW, _ := waiter.NewChannelEntry(inCh)
+				inFile.EventRegister(&inW, eventMaskRead)
+				defer inFile.EventUnregister(&inW)
+				continue // Need to refresh readiness.
+			}
+			if err := t.Block(inCh); err != nil {
+				return 0, nil, err
+			}
+		}
+		if outFile.Readiness(eventMaskWrite)&eventMaskWrite == 0 {
+			if outCh == nil {
+				outCh = make(chan struct{}, 1)
+				outW, _ := waiter.NewChannelEntry(outCh)
+				outFile.EventRegister(&outW, eventMaskWrite)
+				defer outFile.EventUnregister(&outW)
+				continue // Need to refresh readiness.
+			}
+			if err := t.Block(outCh); err != nil {
+				return 0, nil, err
+			}
+		}
+	}
+}
diff --git a/pkg/sentry/syscalls/linux/vfs2/stat.go b/pkg/sentry/syscalls/linux/vfs2/stat.go
index bb1d5cac4..bb1d5cac4 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/stat.go
+++ b/pkg/sentry/syscalls/linux/vfs2/stat.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/stat_amd64.go b/pkg/sentry/syscalls/linux/vfs2/stat_amd64.go
index 2da538fc6..2da538fc6 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/stat_amd64.go
+++ b/pkg/sentry/syscalls/linux/vfs2/stat_amd64.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/stat_arm64.go b/pkg/sentry/syscalls/linux/vfs2/stat_arm64.go
index 88b9c7627..88b9c7627 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/stat_arm64.go
+++ b/pkg/sentry/syscalls/linux/vfs2/stat_arm64.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/sync.go b/pkg/sentry/syscalls/linux/vfs2/sync.go
index 365250b0b..365250b0b 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/sync.go
+++ b/pkg/sentry/syscalls/linux/vfs2/sync.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/timerfd.go b/pkg/sentry/syscalls/linux/vfs2/timerfd.go
index 5ac79bc09..5ac79bc09 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/timerfd.go
+++ b/pkg/sentry/syscalls/linux/vfs2/timerfd.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2.go b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
index a332d01bd..083fdcf82 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
@@ -134,8 +134,8 @@ func Override() {
 	s.Table[269] = syscalls.Supported("faccessat", Faccessat)
 	s.Table[270] = syscalls.Supported("pselect", Pselect)
 	s.Table[271] = syscalls.Supported("ppoll", Ppoll)
-	delete(s.Table, 275) // splice
-	delete(s.Table, 276) // tee
+	s.Table[275] = syscalls.Supported("splice", Splice)
+	s.Table[276] = syscalls.Supported("tee", Tee)
 	s.Table[277] = syscalls.Supported("sync_file_range", SyncFileRange)
 	s.Table[280] = syscalls.Supported("utimensat", Utimensat)
 	s.Table[281] = syscalls.Supported("epoll_pwait", EpollPwait)
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2_abi_autogen_unsafe.go b/pkg/sentry/syscalls/linux/vfs2/vfs2_abi_autogen_unsafe.go
index 372fbcd8e..372fbcd8e 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2_abi_autogen_unsafe.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2_abi_autogen_unsafe.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_abi_autogen_unsafe.go b/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_abi_autogen_unsafe.go
index 204c7ceaf..204c7ceaf 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_abi_autogen_unsafe.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_abi_autogen_unsafe.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_state_autogen.go b/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_state_autogen.go
index 7f5556f9c..7f5556f9c 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_state_autogen.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2_amd64_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_abi_autogen_unsafe.go b/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_abi_autogen_unsafe.go
index 08e10d735..08e10d735 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_abi_autogen_unsafe.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_abi_autogen_unsafe.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_state_autogen.go b/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_state_autogen.go
index 3e3862045..3e3862045 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_state_autogen.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2_arm64_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2_state_autogen.go b/pkg/sentry/syscalls/linux/vfs2/vfs2_state_autogen.go
index 570100331..570100331 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2_state_autogen.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2_state_autogen.go
diff --git a/pkg/sentry/syscalls/linux/vfs2/xattr.go b/pkg/sentry/syscalls/linux/vfs2/xattr.go
index af455d5c1..af455d5c1 100755..100644
--- a/pkg/sentry/syscalls/linux/vfs2/xattr.go
+++ b/pkg/sentry/syscalls/linux/vfs2/xattr.go
diff --git a/pkg/sentry/syscalls/syscalls_state_autogen.go b/pkg/sentry/syscalls/syscalls_state_autogen.go
index b577e39a3..b577e39a3 100755..100644
--- a/pkg/sentry/syscalls/syscalls_state_autogen.go
+++ b/pkg/sentry/syscalls/syscalls_state_autogen.go
diff --git a/pkg/sentry/time/seqatomic_parameters_unsafe.go b/pkg/sentry/time/seqatomic_parameters_unsafe.go
index e2c85d862..efd3ccae2 100755..100644
--- a/pkg/sentry/time/seqatomic_parameters_unsafe.go
+++ b/pkg/sentry/time/seqatomic_parameters_unsafe.go
@@ -1,11 +1,11 @@
 package time
 
 import (
+	"fmt"
 	"reflect"
 	"strings"
 	"unsafe"
 
-	"fmt"
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
diff --git a/pkg/sentry/time/time_arm64_state_autogen.go b/pkg/sentry/time/time_arm64_state_autogen.go
index 2adc9c9e0..2adc9c9e0 100755..100644
--- a/pkg/sentry/time/time_arm64_state_autogen.go
+++ b/pkg/sentry/time/time_arm64_state_autogen.go
diff --git a/pkg/sentry/time/time_state_autogen.go b/pkg/sentry/time/time_state_autogen.go
index 2adc9c9e0..2adc9c9e0 100755..100644
--- a/pkg/sentry/time/time_state_autogen.go
+++ b/pkg/sentry/time/time_state_autogen.go
diff --git a/pkg/sentry/time/time_unsafe_state_autogen.go b/pkg/sentry/time/time_unsafe_state_autogen.go
index 2adc9c9e0..2adc9c9e0 100755..100644
--- a/pkg/sentry/time/time_unsafe_state_autogen.go
+++ b/pkg/sentry/time/time_unsafe_state_autogen.go
diff --git a/pkg/sentry/unimpl/unimpl_state_autogen.go b/pkg/sentry/unimpl/unimpl_state_autogen.go
index b37d16f87..b37d16f87 100755..100644
--- a/pkg/sentry/unimpl/unimpl_state_autogen.go
+++ b/pkg/sentry/unimpl/unimpl_state_autogen.go
diff --git a/pkg/sentry/unimpl/unimplemented_syscall_go_proto/unimplemented_syscall.pb.go b/pkg/sentry/unimpl/unimplemented_syscall_go_proto/unimplemented_syscall.pb.go
index 4dfb169cc..4dfb169cc 100755..100644
--- a/pkg/sentry/unimpl/unimplemented_syscall_go_proto/unimplemented_syscall.pb.go
+++ b/pkg/sentry/unimpl/unimplemented_syscall_go_proto/unimplemented_syscall.pb.go
diff --git a/pkg/sentry/uniqueid/uniqueid_state_autogen.go b/pkg/sentry/uniqueid/uniqueid_state_autogen.go
index 1890fdf46..1890fdf46 100755..100644
--- a/pkg/sentry/uniqueid/uniqueid_state_autogen.go
+++ b/pkg/sentry/uniqueid/uniqueid_state_autogen.go
diff --git a/pkg/sentry/usage/usage_state_autogen.go b/pkg/sentry/usage/usage_state_autogen.go
index 42979ea25..42979ea25 100755..100644
--- a/pkg/sentry/usage/usage_state_autogen.go
+++ b/pkg/sentry/usage/usage_state_autogen.go
diff --git a/pkg/sentry/usage/usage_unsafe_state_autogen.go b/pkg/sentry/usage/usage_unsafe_state_autogen.go
index 5d9e86efa..5d9e86efa 100755..100644
--- a/pkg/sentry/usage/usage_unsafe_state_autogen.go
+++ b/pkg/sentry/usage/usage_unsafe_state_autogen.go
diff --git a/pkg/sentry/vfs/anonfs.go b/pkg/sentry/vfs/anonfs.go
index caf770fd5..caf770fd5 100755..100644
--- a/pkg/sentry/vfs/anonfs.go
+++ b/pkg/sentry/vfs/anonfs.go
diff --git a/pkg/sentry/vfs/context.go b/pkg/sentry/vfs/context.go
index c9e724fef..c9e724fef 100755..100644
--- a/pkg/sentry/vfs/context.go
+++ b/pkg/sentry/vfs/context.go
diff --git a/pkg/sentry/vfs/debug.go b/pkg/sentry/vfs/debug.go
index 0ed20f249..0ed20f249 100755..100644
--- a/pkg/sentry/vfs/debug.go
+++ b/pkg/sentry/vfs/debug.go
diff --git a/pkg/sentry/vfs/dentry.go b/pkg/sentry/vfs/dentry.go
index 8624dbd5d..8624dbd5d 100755..100644
--- a/pkg/sentry/vfs/dentry.go
+++ b/pkg/sentry/vfs/dentry.go
diff --git a/pkg/sentry/vfs/device.go b/pkg/sentry/vfs/device.go
index 1e9dffc8f..1e9dffc8f 100755..100644
--- a/pkg/sentry/vfs/device.go
+++ b/pkg/sentry/vfs/device.go
diff --git a/pkg/sentry/vfs/epoll.go b/pkg/sentry/vfs/epoll.go
index 8297f964b..8297f964b 100755..100644
--- a/pkg/sentry/vfs/epoll.go
+++ b/pkg/sentry/vfs/epoll.go
diff --git a/pkg/sentry/vfs/epoll_interest_list.go b/pkg/sentry/vfs/epoll_interest_list.go
index 67104a9c6..67104a9c6 100755..100644
--- a/pkg/sentry/vfs/epoll_interest_list.go
+++ b/pkg/sentry/vfs/epoll_interest_list.go
diff --git a/pkg/sentry/vfs/file_description.go b/pkg/sentry/vfs/file_description.go
index cfabd936c..bb294563d 100755..100644
--- a/pkg/sentry/vfs/file_description.go
+++ b/pkg/sentry/vfs/file_description.go
@@ -210,6 +210,11 @@ func (fd *FileDescription) VirtualDentry() VirtualDentry {
 	return fd.vd
 }
 
+// Options returns the options passed to fd.Init().
+func (fd *FileDescription) Options() FileDescriptionOptions {
+	return fd.opts
+}
+
 // StatusFlags returns file description status flags, as for fcntl(F_GETFL).
 func (fd *FileDescription) StatusFlags() uint32 {
 	return atomic.LoadUint32(&fd.statusFlags)
diff --git a/pkg/sentry/vfs/file_description_impl_util.go b/pkg/sentry/vfs/file_description_impl_util.go
index f4c111926..f4c111926 100755..100644
--- a/pkg/sentry/vfs/file_description_impl_util.go
+++ b/pkg/sentry/vfs/file_description_impl_util.go
diff --git a/pkg/sentry/vfs/filesystem.go b/pkg/sentry/vfs/filesystem.go
index 1edd584c9..1edd584c9 100755..100644
--- a/pkg/sentry/vfs/filesystem.go
+++ b/pkg/sentry/vfs/filesystem.go
diff --git a/pkg/sentry/vfs/filesystem_impl_util.go b/pkg/sentry/vfs/filesystem_impl_util.go
index 465e610e0..465e610e0 100755..100644
--- a/pkg/sentry/vfs/filesystem_impl_util.go
+++ b/pkg/sentry/vfs/filesystem_impl_util.go
diff --git a/pkg/sentry/vfs/filesystem_type.go b/pkg/sentry/vfs/filesystem_type.go
index f2298f7f6..f2298f7f6 100755..100644
--- a/pkg/sentry/vfs/filesystem_type.go
+++ b/pkg/sentry/vfs/filesystem_type.go
diff --git a/pkg/sentry/vfs/lock/lock.go b/pkg/sentry/vfs/lock/lock.go
index 724dfe743..724dfe743 100755..100644
--- a/pkg/sentry/vfs/lock/lock.go
+++ b/pkg/sentry/vfs/lock/lock.go
diff --git a/pkg/sentry/vfs/lock/lock_state_autogen.go b/pkg/sentry/vfs/lock/lock_state_autogen.go
index 682254baf..682254baf 100755..100644
--- a/pkg/sentry/vfs/lock/lock_state_autogen.go
+++ b/pkg/sentry/vfs/lock/lock_state_autogen.go
diff --git a/pkg/sentry/vfs/memxattr/memxattr_state_autogen.go b/pkg/sentry/vfs/memxattr/memxattr_state_autogen.go
index 6b366cea4..6b366cea4 100755..100644
--- a/pkg/sentry/vfs/memxattr/memxattr_state_autogen.go
+++ b/pkg/sentry/vfs/memxattr/memxattr_state_autogen.go
diff --git a/pkg/sentry/vfs/memxattr/xattr.go b/pkg/sentry/vfs/memxattr/xattr.go
index cc1e7d764..cc1e7d764 100755..100644
--- a/pkg/sentry/vfs/memxattr/xattr.go
+++ b/pkg/sentry/vfs/memxattr/xattr.go
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index 02850b65c..02850b65c 100755..100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
diff --git a/pkg/sentry/vfs/mount_unsafe.go b/pkg/sentry/vfs/mount_unsafe.go
index bc7581698..bc7581698 100755..100644
--- a/pkg/sentry/vfs/mount_unsafe.go
+++ b/pkg/sentry/vfs/mount_unsafe.go
diff --git a/pkg/sentry/vfs/options.go b/pkg/sentry/vfs/options.go
index 53d364c5c..53d364c5c 100755..100644
--- a/pkg/sentry/vfs/options.go
+++ b/pkg/sentry/vfs/options.go
diff --git a/pkg/sentry/vfs/pathname.go b/pkg/sentry/vfs/pathname.go
index cd78d66bc..cd78d66bc 100755..100644
--- a/pkg/sentry/vfs/pathname.go
+++ b/pkg/sentry/vfs/pathname.go
diff --git a/pkg/sentry/vfs/permissions.go b/pkg/sentry/vfs/permissions.go
index f9647f90e..f9647f90e 100755..100644
--- a/pkg/sentry/vfs/permissions.go
+++ b/pkg/sentry/vfs/permissions.go
diff --git a/pkg/sentry/vfs/resolving_path.go b/pkg/sentry/vfs/resolving_path.go
index 9d047ff88..9d047ff88 100755..100644
--- a/pkg/sentry/vfs/resolving_path.go
+++ b/pkg/sentry/vfs/resolving_path.go
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 8d7f8f8af..8d7f8f8af 100755..100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
diff --git a/pkg/sentry/vfs/vfs_state_autogen.go b/pkg/sentry/vfs/vfs_state_autogen.go
index 0cf6ed48d..0cf6ed48d 100755..100644
--- a/pkg/sentry/vfs/vfs_state_autogen.go
+++ b/pkg/sentry/vfs/vfs_state_autogen.go
diff --git a/pkg/sentry/vfs/vfs_unsafe_state_autogen.go b/pkg/sentry/vfs/vfs_unsafe_state_autogen.go
index 8b198c5dd..8b198c5dd 100755..100644
--- a/pkg/sentry/vfs/vfs_unsafe_state_autogen.go
+++ b/pkg/sentry/vfs/vfs_unsafe_state_autogen.go
diff --git a/pkg/sentry/watchdog/watchdog_state_autogen.go b/pkg/sentry/watchdog/watchdog_state_autogen.go
index bce0200e7..bce0200e7 100755..100644
--- a/pkg/sentry/watchdog/watchdog_state_autogen.go
+++ b/pkg/sentry/watchdog/watchdog_state_autogen.go
diff --git a/pkg/sleep/commit_arm64.s b/pkg/sleep/commit_arm64.s
index d0ef15b20..d0ef15b20 100755..100644
--- a/pkg/sleep/commit_arm64.s
+++ b/pkg/sleep/commit_arm64.s
diff --git a/pkg/sleep/sleep_state_autogen.go b/pkg/sleep/sleep_state_autogen.go
index 39986b478..39986b478 100755..100644
--- a/pkg/sleep/sleep_state_autogen.go
+++ b/pkg/sleep/sleep_state_autogen.go
diff --git a/pkg/sleep/sleep_unsafe_state_autogen.go b/pkg/sleep/sleep_unsafe_state_autogen.go
index 023c828d7..023c828d7 100755..100644
--- a/pkg/sleep/sleep_unsafe_state_autogen.go
+++ b/pkg/sleep/sleep_unsafe_state_autogen.go
diff --git a/pkg/state/addr_range.go b/pkg/state/addr_range.go
index 45720c643..45720c643 100755..100644
--- a/pkg/state/addr_range.go
+++ b/pkg/state/addr_range.go
diff --git a/pkg/state/addr_set.go b/pkg/state/addr_set.go
index 5261aa488..f8eaf0cd1 100755..100644
--- a/pkg/state/addr_set.go
+++ b/pkg/state/addr_set.go
@@ -9,6 +9,34 @@ import (
 	"fmt"
 )
 
+// trackGaps is an optional parameter.
+//
+// If trackGaps is 1, the Set will track maximum gap size recursively,
+// enabling the GapIterator.{Prev,Next}LargeEnoughGap functions. In this
+// case, Key must be an unsigned integer.
+//
+// trackGaps must be 0 or 1.
+const addrtrackGaps = 0
+
+var _ = uint8(addrtrackGaps << 7) // Will fail if not zero or one.
+
+// dynamicGap is a type that disappears if trackGaps is 0.
+type addrdynamicGap [addrtrackGaps]uintptr
+
+// Get returns the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *addrdynamicGap) Get() uintptr {
+	return d[:][0]
+}
+
+// Set sets the value of the gap.
+//
+// Precondition: trackGaps must be non-zero.
+func (d *addrdynamicGap) Set(v uintptr) {
+	d[:][0] = v
+}
+
 const (
 	// minDegree is the minimum degree of an internal node in a Set B-tree.
 	//
@@ -267,8 +295,12 @@ func (s *addrSet) Insert(gap addrGapIterator, r addrRange, val __generics_import
 	}
 	if prev.Ok() && prev.End() == r.Start {
 		if mval, ok := (addrSetFunctions{}).Merge(prev.Range(), prev.Value(), r, val); ok {
+			shrinkMaxGap := addrtrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			prev.SetEndUnchecked(r.End)
 			prev.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			if next.Ok() && next.Start() == r.End {
 				val = mval
 				if mval, ok := (addrSetFunctions{}).Merge(prev.Range(), val, next.Range(), next.Value()); ok {
@@ -282,11 +314,16 @@ func (s *addrSet) Insert(gap addrGapIterator, r addrRange, val __generics_import
 	}
 	if next.Ok() && next.Start() == r.End {
 		if mval, ok := (addrSetFunctions{}).Merge(r, val, next.Range(), next.Value()); ok {
+			shrinkMaxGap := addrtrackGaps != 0 && gap.Range().Length() == gap.node.maxGap.Get()
 			next.SetStartUnchecked(r.Start)
 			next.SetValue(mval)
+			if shrinkMaxGap {
+				gap.node.updateMaxGapLeaf()
+			}
 			return next
 		}
 	}
+
 	return s.InsertWithoutMergingUnchecked(gap, r, val)
 }
 
@@ -313,11 +350,15 @@ func (s *addrSet) InsertWithoutMerging(gap addrGapIterator, r addrRange, val __g
 // Preconditions: r.Start >= gap.Start(); r.End <= gap.End().
 func (s *addrSet) InsertWithoutMergingUnchecked(gap addrGapIterator, r addrRange, val __generics_imported0.Value) addrIterator {
 	gap = gap.node.rebalanceBeforeInsert(gap)
+	splitMaxGap := addrtrackGaps != 0 && (gap.node.nrSegments == 0 || gap.Range().Length() == gap.node.maxGap.Get())
 	copy(gap.node.keys[gap.index+1:], gap.node.keys[gap.index:gap.node.nrSegments])
 	copy(gap.node.values[gap.index+1:], gap.node.values[gap.index:gap.node.nrSegments])
 	gap.node.keys[gap.index] = r
 	gap.node.values[gap.index] = val
 	gap.node.nrSegments++
+	if splitMaxGap {
+		gap.node.updateMaxGapLeaf()
+	}
 	return addrIterator{gap.node, gap.index}
 }
 
@@ -332,12 +373,20 @@ func (s *addrSet) Remove(seg addrIterator) addrGapIterator {
 
 		seg.SetRangeUnchecked(victim.Range())
 		seg.SetValue(victim.Value())
+
+		nextAdjacentNode := seg.NextSegment().node
+		if addrtrackGaps != 0 {
+			nextAdjacentNode.updateMaxGapLeaf()
+		}
 		return s.Remove(victim).NextGap()
 	}
 	copy(seg.node.keys[seg.index:], seg.node.keys[seg.index+1:seg.node.nrSegments])
 	copy(seg.node.values[seg.index:], seg.node.values[seg.index+1:seg.node.nrSegments])
 	addrSetFunctions{}.ClearValue(&seg.node.values[seg.node.nrSegments-1])
 	seg.node.nrSegments--
+	if addrtrackGaps != 0 {
+		seg.node.updateMaxGapLeaf()
+	}
 	return seg.node.rebalanceAfterRemove(addrGapIterator{seg.node, seg.index})
 }
 
@@ -387,6 +436,7 @@ func (s *addrSet) MergeUnchecked(first, second addrIterator) addrIterator {
 
 			first.SetEndUnchecked(second.End())
 			first.SetValue(mval)
+
 			return s.Remove(second).PrevSegment()
 		}
 	}
@@ -562,6 +612,12 @@ type addrnode struct {
 	// than "isLeaf" because false must be the correct value for an empty root.
 	hasChildren bool
 
+	// The longest gap within this node. If the node is a leaf, it's simply the
+	// maximum gap among all the (nrSegments+1) gaps formed by its nrSegments keys
+	// including the 0th and nrSegments-th gap possibly shared with its upper-level
+	// nodes; if it's a non-leaf node, it's the max of all children's maxGap.
+	maxGap addrdynamicGap
+
 	// Nodes store keys and values in separate arrays to maximize locality in
 	// the common case (scanning keys for lookup).
 	keys     [addrmaxDegree - 1]addrRange
@@ -607,12 +663,12 @@ func (n *addrnode) nextSibling() *addrnode {
 // required for insertion, and returns an updated iterator to the position
 // represented by gap.
 func (n *addrnode) rebalanceBeforeInsert(gap addrGapIterator) addrGapIterator {
-	if n.parent != nil {
-		gap = n.parent.rebalanceBeforeInsert(gap)
-	}
 	if n.nrSegments < addrmaxDegree-1 {
 		return gap
 	}
+	if n.parent != nil {
+		gap = n.parent.rebalanceBeforeInsert(gap)
+	}
 	if n.parent == nil {
 
 		left := &addrnode{
@@ -648,6 +704,11 @@ func (n *addrnode) rebalanceBeforeInsert(gap addrGapIterator) addrGapIterator {
 		n.hasChildren = true
 		n.children[0] = left
 		n.children[1] = right
+
+		if addrtrackGaps != 0 {
+			left.updateMaxGapLocal()
+			right.updateMaxGapLocal()
+		}
 		if gap.node != n {
 			return gap
 		}
@@ -685,6 +746,11 @@ func (n *addrnode) rebalanceBeforeInsert(gap addrGapIterator) addrGapIterator {
 	}
 	n.nrSegments = addrminDegree - 1
 
+	if addrtrackGaps != 0 {
+		n.updateMaxGapLocal()
+		sibling.updateMaxGapLocal()
+	}
+
 	if gap.node != n {
 		return gap
 	}
@@ -730,6 +796,11 @@ func (n *addrnode) rebalanceAfterRemove(gap addrGapIterator) addrGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if addrtrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling && gap.index == sibling.nrSegments {
 				return addrGapIterator{n, 0}
 			}
@@ -758,6 +829,11 @@ func (n *addrnode) rebalanceAfterRemove(gap addrGapIterator) addrGapIterator {
 			}
 			n.nrSegments++
 			sibling.nrSegments--
+
+			if addrtrackGaps != 0 {
+				n.updateMaxGapLocal()
+				sibling.updateMaxGapLocal()
+			}
 			if gap.node == sibling {
 				if gap.index == 0 {
 					return addrGapIterator{n, n.nrSegments}
@@ -790,6 +866,7 @@ func (n *addrnode) rebalanceAfterRemove(gap addrGapIterator) addrGapIterator {
 				p.children[0] = nil
 				p.children[1] = nil
 			}
+
 			if gap.node == left {
 				return addrGapIterator{p, gap.index}
 			}
@@ -836,10 +913,146 @@ func (n *addrnode) rebalanceAfterRemove(gap addrGapIterator) addrGapIterator {
 		p.children[p.nrSegments] = nil
 		p.nrSegments--
 
+		if addrtrackGaps != 0 {
+			left.updateMaxGapLocal()
+		}
+
 		n = p
 	}
 }
 
+// updateMaxGapLeaf updates maxGap bottom-up from the calling leaf until no
+// necessary update.
+//
+// Preconditions: n must be a leaf node, trackGaps must be 1.
+func (n *addrnode) updateMaxGapLeaf() {
+	if n.hasChildren {
+		panic(fmt.Sprintf("updateMaxGapLeaf should always be called on leaf node: %v", n))
+	}
+	max := n.calculateMaxGapLeaf()
+	if max == n.maxGap.Get() {
+
+		return
+	}
+	oldMax := n.maxGap.Get()
+	n.maxGap.Set(max)
+	if max > oldMax {
+
+		for p := n.parent; p != nil; p = p.parent {
+			if p.maxGap.Get() >= max {
+
+				break
+			}
+
+			p.maxGap.Set(max)
+		}
+		return
+	}
+
+	for p := n.parent; p != nil; p = p.parent {
+		if p.maxGap.Get() > oldMax {
+
+			break
+		}
+
+		parentNewMax := p.calculateMaxGapInternal()
+		if p.maxGap.Get() == parentNewMax {
+
+			break
+		}
+
+		p.maxGap.Set(parentNewMax)
+	}
+}
+
+// updateMaxGapLocal updates maxGap of the calling node solely with no
+// propagation to ancestor nodes.
+//
+// Precondition: trackGaps must be 1.
+func (n *addrnode) updateMaxGapLocal() {
+	if !n.hasChildren {
+
+		n.maxGap.Set(n.calculateMaxGapLeaf())
+	} else {
+
+		n.maxGap.Set(n.calculateMaxGapInternal())
+	}
+}
+
+// calculateMaxGapLeaf iterates the gaps within a leaf node and calculate the
+// max.
+//
+// Preconditions: n must be a leaf node.
+func (n *addrnode) calculateMaxGapLeaf() uintptr {
+	max := addrGapIterator{n, 0}.Range().Length()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := (addrGapIterator{n, i}).Range().Length(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// calculateMaxGapInternal iterates children's maxGap within an internal node n
+// and calculate the max.
+//
+// Preconditions: n must be a non-leaf node.
+func (n *addrnode) calculateMaxGapInternal() uintptr {
+	max := n.children[0].maxGap.Get()
+	for i := 1; i <= n.nrSegments; i++ {
+		if current := n.children[i].maxGap.Get(); current > max {
+			max = current
+		}
+	}
+	return max
+}
+
+// searchFirstLargeEnoughGap returns the first gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *addrnode) searchFirstLargeEnoughGap(minSize uintptr) addrGapIterator {
+	if n.maxGap.Get() < minSize {
+		return addrGapIterator{}
+	}
+	if n.hasChildren {
+		for i := 0; i <= n.nrSegments; i++ {
+			if largeEnoughGap := n.children[i].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := 0; i <= n.nrSegments; i++ {
+			currentGap := addrGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
+// searchLastLargeEnoughGap returns the last gap having at least minSize length
+// in the subtree rooted by n. If not found, return a terminal gap iterator.
+func (n *addrnode) searchLastLargeEnoughGap(minSize uintptr) addrGapIterator {
+	if n.maxGap.Get() < minSize {
+		return addrGapIterator{}
+	}
+	if n.hasChildren {
+		for i := n.nrSegments; i >= 0; i-- {
+			if largeEnoughGap := n.children[i].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		}
+	} else {
+		for i := n.nrSegments; i >= 0; i-- {
+			currentGap := addrGapIterator{n, i}
+			if currentGap.Range().Length() >= minSize {
+				return currentGap
+			}
+		}
+	}
+	panic(fmt.Sprintf("invalid maxGap in %v", n))
+}
+
 // A Iterator is conceptually one of:
 //
 // - A pointer to a segment in a set; or
@@ -1145,6 +1358,114 @@ func (gap addrGapIterator) NextGap() addrGapIterator {
 	return seg.NextGap()
 }
 
+// NextLargeEnoughGap returns the iterated gap's first next gap with larger
+// length than minSize.  If not found, return a terminal gap iterator (does NOT
+// include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap addrGapIterator) NextLargeEnoughGap(minSize uintptr) addrGapIterator {
+	if addrtrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == gap.node.nrSegments {
+
+		gap.node = gap.NextSegment().node
+		gap.index = 0
+		return gap.nextLargeEnoughGapHelper(minSize)
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// nextLargeEnoughGapHelper is the helper function used by NextLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the trailing gap of a non-leaf node.
+func (gap addrGapIterator) nextLargeEnoughGapHelper(minSize uintptr) addrGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == gap.node.nrSegments)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return addrGapIterator{}
+	}
+
+	gap.index++
+	for gap.index <= gap.node.nrSegments {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchFirstLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index++
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == gap.node.nrSegments {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.nextLargeEnoughGapHelper(minSize)
+}
+
+// PrevLargeEnoughGap returns the iterated gap's first prev gap with larger or
+// equal length than minSize.  If not found, return a terminal gap iterator
+// (does NOT include this gap itself).
+//
+// Precondition: trackGaps must be 1.
+func (gap addrGapIterator) PrevLargeEnoughGap(minSize uintptr) addrGapIterator {
+	if addrtrackGaps != 1 {
+		panic("set is not tracking gaps")
+	}
+	if gap.node != nil && gap.node.hasChildren && gap.index == 0 {
+
+		gap.node = gap.PrevSegment().node
+		gap.index = gap.node.nrSegments
+		return gap.prevLargeEnoughGapHelper(minSize)
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
+// prevLargeEnoughGapHelper is the helper function used by PrevLargeEnoughGap
+// to do the real recursions.
+//
+// Preconditions: gap is NOT the first gap of a non-leaf node.
+func (gap addrGapIterator) prevLargeEnoughGapHelper(minSize uintptr) addrGapIterator {
+
+	for gap.node != nil &&
+		(gap.node.maxGap.Get() < minSize || (!gap.node.hasChildren && gap.index == 0)) {
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+
+	if gap.node == nil {
+		return addrGapIterator{}
+	}
+
+	gap.index--
+	for gap.index >= 0 {
+		if gap.node.hasChildren {
+			if largeEnoughGap := gap.node.children[gap.index].searchLastLargeEnoughGap(minSize); largeEnoughGap.Ok() {
+				return largeEnoughGap
+			}
+		} else {
+			if gap.Range().Length() >= minSize {
+				return gap
+			}
+		}
+		gap.index--
+	}
+	gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	if gap.node != nil && gap.index == 0 {
+
+		gap.node, gap.index = gap.node.parent, gap.node.parentIndex
+	}
+	return gap.prevLargeEnoughGapHelper(minSize)
+}
+
 // segmentBeforePosition returns the predecessor segment of the position given
 // by n.children[i], which may or may not contain a child. If no such segment
 // exists, segmentBeforePosition returns a terminal iterator.
@@ -1211,7 +1532,15 @@ func (n *addrnode) writeDebugString(buf *bytes.Buffer, prefix string) {
 			child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, i))
 		}
 		buf.WriteString(prefix)
-		buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		if n.hasChildren {
+			if addrtrackGaps != 0 {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v, maxGap: %d\n", i, n.keys[i], n.values[i], n.maxGap.Get()))
+			} else {
+				buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+			}
+		} else {
+			buf.WriteString(fmt.Sprintf("- % 3d: %v => %v\n", i, n.keys[i], n.values[i]))
+		}
 	}
 	if child := n.children[n.nrSegments]; child != nil {
 		child.writeDebugString(buf, fmt.Sprintf("%s- % 3d ", prefix, n.nrSegments))
@@ -1263,6 +1592,46 @@ func (s *addrSet) ImportSortedSlices(sds *addrSegmentDataSlices) error {
 	}
 	return nil
 }
+
+// segmentTestCheck returns an error if s is incorrectly sorted, does not
+// contain exactly expectedSegments segments, or contains a segment which
+// fails the passed check.
+//
+// This should be used only for testing, and has been added to this package for
+// templating convenience.
+func (s *addrSet) segmentTestCheck(expectedSegments int, segFunc func(int, addrRange, __generics_imported0.Value) error) error {
+	havePrev := false
+	prev := uintptr(0)
+	nrSegments := 0
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		next := seg.Start()
+		if havePrev && prev >= next {
+			return fmt.Errorf("incorrect order: key %d (segment %d) >= key %d (segment %d)", prev, nrSegments-1, next, nrSegments)
+		}
+		if segFunc != nil {
+			if err := segFunc(nrSegments, seg.Range(), seg.Value()); err != nil {
+				return err
+			}
+		}
+		prev = next
+		havePrev = true
+		nrSegments++
+	}
+	if nrSegments != expectedSegments {
+		return fmt.Errorf("incorrect number of segments: got %d, wanted %d", nrSegments, expectedSegments)
+	}
+	return nil
+}
+
+// countSegments counts the number of segments in the set.
+//
+// Similar to Check, this should only be used for testing.
+func (s *addrSet) countSegments() (segments int) {
+	for seg := s.FirstSegment(); seg.Ok(); seg = seg.NextSegment() {
+		segments++
+	}
+	return segments
+}
 func (s *addrSet) saveRoot() *addrSegmentDataSlices {
 	return s.ExportSortedSlices()
 }
diff --git a/pkg/state/object_go_proto/object.pb.go b/pkg/state/object_go_proto/object.pb.go
index dc5127149..dc5127149 100755..100644
--- a/pkg/state/object_go_proto/object.pb.go
+++ b/pkg/state/object_go_proto/object.pb.go
diff --git a/pkg/state/statefile/statefile_state_autogen.go b/pkg/state/statefile/statefile_state_autogen.go
index a2cdaa3f1..a2cdaa3f1 100755..100644
--- a/pkg/state/statefile/statefile_state_autogen.go
+++ b/pkg/state/statefile/statefile_state_autogen.go
diff --git a/pkg/sync/aliases.go b/pkg/sync/aliases.go
index 0d4316254..0d4316254 100755..100644
--- a/pkg/sync/aliases.go
+++ b/pkg/sync/aliases.go
diff --git a/pkg/sync/memmove_unsafe.go b/pkg/sync/memmove_unsafe.go
index ad4a3a37e..ad4a3a37e 100755..100644
--- a/pkg/sync/memmove_unsafe.go
+++ b/pkg/sync/memmove_unsafe.go
diff --git a/pkg/sync/mutex_unsafe.go b/pkg/sync/mutex_unsafe.go
index 3dd15578b..3dd15578b 100755..100644
--- a/pkg/sync/mutex_unsafe.go
+++ b/pkg/sync/mutex_unsafe.go
diff --git a/pkg/sync/norace_unsafe.go b/pkg/sync/norace_unsafe.go
index 006055dd6..006055dd6 100755..100644
--- a/pkg/sync/norace_unsafe.go
+++ b/pkg/sync/norace_unsafe.go
diff --git a/pkg/sync/race_unsafe.go b/pkg/sync/race_unsafe.go
index 31d8fa9a6..31d8fa9a6 100755..100644
--- a/pkg/sync/race_unsafe.go
+++ b/pkg/sync/race_unsafe.go
diff --git a/pkg/sync/rwmutex_unsafe.go b/pkg/sync/rwmutex_unsafe.go
index ea6cdc447..ea6cdc447 100755..100644
--- a/pkg/sync/rwmutex_unsafe.go
+++ b/pkg/sync/rwmutex_unsafe.go
diff --git a/pkg/sync/seqcount.go b/pkg/sync/seqcount.go
index a1e895352..a1e895352 100755..100644
--- a/pkg/sync/seqcount.go
+++ b/pkg/sync/seqcount.go
diff --git a/pkg/sync/sync.go b/pkg/sync/sync.go
index b16cf5333..b16cf5333 100755..100644
--- a/pkg/sync/sync.go
+++ b/pkg/sync/sync.go
diff --git a/pkg/sync/sync_state_autogen.go b/pkg/sync/sync_state_autogen.go
deleted file mode 100755
index c6dc2c7e7..000000000
--- a/pkg/sync/sync_state_autogen.go
+++ /dev/null
@@ -1,3 +0,0 @@
-// automatically generated by stateify.
-
-package sync
diff --git a/pkg/sync/sync_unsafe_state_autogen.go b/pkg/sync/sync_unsafe_state_autogen.go
deleted file mode 100755
index 6876ee883..000000000
--- a/pkg/sync/sync_unsafe_state_autogen.go
+++ /dev/null
@@ -1,12 +0,0 @@
-// automatically generated by stateify.
-
-// +build go1.12
-// +build !go1.15
-// +build go1.13
-// +build !go1.15
-// +build !race
-// +build race
-// +build go1.13
-// +build !go1.15
-
-package sync
diff --git a/pkg/syserr/syserr_linux_state_autogen.go b/pkg/syserr/syserr_linux_state_autogen.go
index 7fd5a68b8..7fd5a68b8 100755..100644
--- a/pkg/syserr/syserr_linux_state_autogen.go
+++ b/pkg/syserr/syserr_linux_state_autogen.go
diff --git a/pkg/syserr/syserr_state_autogen.go b/pkg/syserr/syserr_state_autogen.go
index 712631a64..712631a64 100755..100644
--- a/pkg/syserr/syserr_state_autogen.go
+++ b/pkg/syserr/syserr_state_autogen.go
diff --git a/pkg/syserror/syserror_state_autogen.go b/pkg/syserror/syserror_state_autogen.go
index 456dcf093..456dcf093 100755..100644
--- a/pkg/syserror/syserror_state_autogen.go
+++ b/pkg/syserror/syserror_state_autogen.go
diff --git a/pkg/tcpip/adapters/gonet/gonet.go b/pkg/tcpip/adapters/gonet/gonet.go
index 6e0db2741..6e0db2741 100755..100644
--- a/pkg/tcpip/adapters/gonet/gonet.go
+++ b/pkg/tcpip/adapters/gonet/gonet.go
diff --git a/pkg/tcpip/adapters/gonet/gonet_state_autogen.go b/pkg/tcpip/adapters/gonet/gonet_state_autogen.go
index 7a5c5419e..7a5c5419e 100755..100644
--- a/pkg/tcpip/adapters/gonet/gonet_state_autogen.go
+++ b/pkg/tcpip/adapters/gonet/gonet_state_autogen.go
diff --git a/pkg/tcpip/buffer/buffer_state_autogen.go b/pkg/tcpip/buffer/buffer_state_autogen.go
index 954487771..954487771 100755..100644
--- a/pkg/tcpip/buffer/buffer_state_autogen.go
+++ b/pkg/tcpip/buffer/buffer_state_autogen.go
diff --git a/pkg/tcpip/hash/jenkins/jenkins_state_autogen.go b/pkg/tcpip/hash/jenkins/jenkins_state_autogen.go
index 216cc5a2e..216cc5a2e 100755..100644
--- a/pkg/tcpip/hash/jenkins/jenkins_state_autogen.go
+++ b/pkg/tcpip/hash/jenkins/jenkins_state_autogen.go
diff --git a/pkg/tcpip/header/header_state_autogen.go b/pkg/tcpip/header/header_state_autogen.go
index 015d7e12a..015d7e12a 100755..100644
--- a/pkg/tcpip/header/header_state_autogen.go
+++ b/pkg/tcpip/header/header_state_autogen.go
diff --git a/pkg/tcpip/header/ipv6_extension_headers.go b/pkg/tcpip/header/ipv6_extension_headers.go
index 2c4591409..2c4591409 100755..100644
--- a/pkg/tcpip/header/ipv6_extension_headers.go
+++ b/pkg/tcpip/header/ipv6_extension_headers.go
diff --git a/pkg/tcpip/header/ndp_neighbor_advert.go b/pkg/tcpip/header/ndp_neighbor_advert.go
index 505c92668..505c92668 100755..100644
--- a/pkg/tcpip/header/ndp_neighbor_advert.go
+++ b/pkg/tcpip/header/ndp_neighbor_advert.go
diff --git a/pkg/tcpip/header/ndp_neighbor_solicit.go b/pkg/tcpip/header/ndp_neighbor_solicit.go
index 3a1b8e139..3a1b8e139 100755..100644
--- a/pkg/tcpip/header/ndp_neighbor_solicit.go
+++ b/pkg/tcpip/header/ndp_neighbor_solicit.go
diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go
index 5d3975c56..5d3975c56 100755..100644
--- a/pkg/tcpip/header/ndp_options.go
+++ b/pkg/tcpip/header/ndp_options.go
diff --git a/pkg/tcpip/header/ndp_router_advert.go b/pkg/tcpip/header/ndp_router_advert.go
index bf7610863..bf7610863 100755..100644
--- a/pkg/tcpip/header/ndp_router_advert.go
+++ b/pkg/tcpip/header/ndp_router_advert.go
diff --git a/pkg/tcpip/header/ndp_router_solicit.go b/pkg/tcpip/header/ndp_router_solicit.go
index 9e67ba95d..9e67ba95d 100755..100644
--- a/pkg/tcpip/header/ndp_router_solicit.go
+++ b/pkg/tcpip/header/ndp_router_solicit.go
diff --git a/pkg/tcpip/header/ndpoptionidentifier_string.go b/pkg/tcpip/header/ndpoptionidentifier_string.go
index 6fe9a336b..6fe9a336b 100755..100644
--- a/pkg/tcpip/header/ndpoptionidentifier_string.go
+++ b/pkg/tcpip/header/ndpoptionidentifier_string.go
diff --git a/pkg/tcpip/header/tcp.go b/pkg/tcpip/header/tcp.go
index 29454c4b9..4c6f808e5 100644
--- a/pkg/tcpip/header/tcp.go
+++ b/pkg/tcpip/header/tcp.go
@@ -66,6 +66,14 @@ const (
 	TCPOptionSACK          = 5
 )
 
+// Option Lengths.
+const (
+	TCPOptionMSSLength           = 4
+	TCPOptionTSLength            = 10
+	TCPOptionWSLength            = 3
+	TCPOptionSackPermittedLength = 2
+)
+
 // TCPFields contains the fields of a TCP packet. It is used to describe the
 // fields of a packet that needs to be encoded.
 type TCPFields struct {
@@ -494,14 +502,11 @@ func ParseTCPOptions(b []byte) TCPOptions {
 // returns without encoding anything. It returns the number of bytes written to
 // the provided buffer.
 func EncodeMSSOption(mss uint32, b []byte) int {
-	// mssOptionSize is the number of bytes in a valid MSS option.
-	const mssOptionSize = 4
-
-	if len(b) < mssOptionSize {
+	if len(b) < TCPOptionMSSLength {
 		return 0
 	}
-	b[0], b[1], b[2], b[3] = TCPOptionMSS, mssOptionSize, byte(mss>>8), byte(mss)
-	return mssOptionSize
+	b[0], b[1], b[2], b[3] = TCPOptionMSS, TCPOptionMSSLength, byte(mss>>8), byte(mss)
+	return TCPOptionMSSLength
 }
 
 // EncodeWSOption encodes the WS TCP option with the WS value in the
@@ -509,10 +514,10 @@ func EncodeMSSOption(mss uint32, b []byte) int {
 // returns without encoding anything. It returns the number of bytes written to
 // the provided buffer.
 func EncodeWSOption(ws int, b []byte) int {
-	if len(b) < 3 {
+	if len(b) < TCPOptionWSLength {
 		return 0
 	}
-	b[0], b[1], b[2] = TCPOptionWS, 3, uint8(ws)
+	b[0], b[1], b[2] = TCPOptionWS, TCPOptionWSLength, uint8(ws)
 	return int(b[1])
 }
 
@@ -521,10 +526,10 @@ func EncodeWSOption(ws int, b []byte) int {
 // just returns without encoding anything. It returns the number of bytes
 // written to the provided buffer.
 func EncodeTSOption(tsVal, tsEcr uint32, b []byte) int {
-	if len(b) < 10 {
+	if len(b) < TCPOptionTSLength {
 		return 0
 	}
-	b[0], b[1] = TCPOptionTS, 10
+	b[0], b[1] = TCPOptionTS, TCPOptionTSLength
 	binary.BigEndian.PutUint32(b[2:], tsVal)
 	binary.BigEndian.PutUint32(b[6:], tsEcr)
 	return int(b[1])
@@ -535,11 +540,11 @@ func EncodeTSOption(tsVal, tsEcr uint32, b []byte) int {
 // encoding anything. It returns the number of bytes written to the provided
 // buffer.
 func EncodeSACKPermittedOption(b []byte) int {
-	if len(b) < 2 {
+	if len(b) < TCPOptionSackPermittedLength {
 		return 0
 	}
 
-	b[0], b[1] = TCPOptionSACKPermitted, 2
+	b[0], b[1] = TCPOptionSACKPermitted, TCPOptionSackPermittedLength
 	return int(b[1])
 }
 
diff --git a/pkg/tcpip/link/channel/channel.go b/pkg/tcpip/link/channel/channel.go
index 9bf67686d..9bf67686d 100755..100644
--- a/pkg/tcpip/link/channel/channel.go
+++ b/pkg/tcpip/link/channel/channel.go
diff --git a/pkg/tcpip/link/channel/channel_state_autogen.go b/pkg/tcpip/link/channel/channel_state_autogen.go
index ce52482a2..ce52482a2 100755..100644
--- a/pkg/tcpip/link/channel/channel_state_autogen.go
+++ b/pkg/tcpip/link/channel/channel_state_autogen.go
diff --git a/pkg/tcpip/link/fdbased/fdbased_state_autogen.go b/pkg/tcpip/link/fdbased/fdbased_state_autogen.go
index b84e8f21c..b84e8f21c 100755..100644
--- a/pkg/tcpip/link/fdbased/fdbased_state_autogen.go
+++ b/pkg/tcpip/link/fdbased/fdbased_state_autogen.go
diff --git a/pkg/tcpip/link/fdbased/fdbased_unsafe_state_autogen.go b/pkg/tcpip/link/fdbased/fdbased_unsafe_state_autogen.go
index e2ed505b2..e2ed505b2 100755..100644
--- a/pkg/tcpip/link/fdbased/fdbased_unsafe_state_autogen.go
+++ b/pkg/tcpip/link/fdbased/fdbased_unsafe_state_autogen.go
diff --git a/pkg/tcpip/link/fdbased/packet_dispatchers.go b/pkg/tcpip/link/fdbased/packet_dispatchers.go
index cb4cbea69..3aaabd1aa 100644
--- a/pkg/tcpip/link/fdbased/packet_dispatchers.go
+++ b/pkg/tcpip/link/fdbased/packet_dispatchers.go
@@ -169,7 +169,7 @@ type recvMMsgDispatcher struct {
 
 	// iovecs is an array of array of iovec records where each iovec base
 	// pointer and length are initialzed to the corresponding view above,
-	// except when GSO is neabled then the first iovec in each array of
+	// except when GSO is enabled then the first iovec in each array of
 	// iovecs points to a buffer for the vnet header which is stripped
 	// before the views are passed up the stack for further processing.
 	iovecs [][]syscall.Iovec
diff --git a/pkg/tcpip/link/loopback/loopback_state_autogen.go b/pkg/tcpip/link/loopback/loopback_state_autogen.go
index c00fd9f19..c00fd9f19 100755..100644
--- a/pkg/tcpip/link/loopback/loopback_state_autogen.go
+++ b/pkg/tcpip/link/loopback/loopback_state_autogen.go
diff --git a/pkg/tcpip/link/muxed/injectable.go b/pkg/tcpip/link/muxed/injectable.go
index a5478ce17..a5478ce17 100755..100644
--- a/pkg/tcpip/link/muxed/injectable.go
+++ b/pkg/tcpip/link/muxed/injectable.go
diff --git a/pkg/tcpip/link/muxed/muxed_state_autogen.go b/pkg/tcpip/link/muxed/muxed_state_autogen.go
index 56330e2a5..56330e2a5 100755..100644
--- a/pkg/tcpip/link/muxed/muxed_state_autogen.go
+++ b/pkg/tcpip/link/muxed/muxed_state_autogen.go
diff --git a/pkg/tcpip/link/qdisc/fifo/endpoint.go b/pkg/tcpip/link/qdisc/fifo/endpoint.go
index 54432194d..54432194d 100755..100644
--- a/pkg/tcpip/link/qdisc/fifo/endpoint.go
+++ b/pkg/tcpip/link/qdisc/fifo/endpoint.go
diff --git a/pkg/tcpip/link/qdisc/fifo/fifo_state_autogen.go b/pkg/tcpip/link/qdisc/fifo/fifo_state_autogen.go
index 9eb52b1cb..9eb52b1cb 100755..100644
--- a/pkg/tcpip/link/qdisc/fifo/fifo_state_autogen.go
+++ b/pkg/tcpip/link/qdisc/fifo/fifo_state_autogen.go
diff --git a/pkg/tcpip/link/qdisc/fifo/packet_buffer_queue.go b/pkg/tcpip/link/qdisc/fifo/packet_buffer_queue.go
index eb5abb906..eb5abb906 100755..100644
--- a/pkg/tcpip/link/qdisc/fifo/packet_buffer_queue.go
+++ b/pkg/tcpip/link/qdisc/fifo/packet_buffer_queue.go
diff --git a/pkg/tcpip/link/rawfile/rawfile_state_autogen.go b/pkg/tcpip/link/rawfile/rawfile_state_autogen.go
index 338e9679b..338e9679b 100755..100644
--- a/pkg/tcpip/link/rawfile/rawfile_state_autogen.go
+++ b/pkg/tcpip/link/rawfile/rawfile_state_autogen.go
diff --git a/pkg/tcpip/link/rawfile/rawfile_unsafe_state_autogen.go b/pkg/tcpip/link/rawfile/rawfile_unsafe_state_autogen.go
index 70d62c4a1..70d62c4a1 100755..100644
--- a/pkg/tcpip/link/rawfile/rawfile_unsafe_state_autogen.go
+++ b/pkg/tcpip/link/rawfile/rawfile_unsafe_state_autogen.go
diff --git a/pkg/tcpip/link/sharedmem/pipe/pipe.go b/pkg/tcpip/link/sharedmem/pipe/pipe.go
index 74c9f0311..74c9f0311 100755..100644
--- a/pkg/tcpip/link/sharedmem/pipe/pipe.go
+++ b/pkg/tcpip/link/sharedmem/pipe/pipe.go
diff --git a/pkg/tcpip/link/sharedmem/pipe/pipe_state_autogen.go b/pkg/tcpip/link/sharedmem/pipe/pipe_state_autogen.go
index d3b40feb4..d3b40feb4 100755..100644
--- a/pkg/tcpip/link/sharedmem/pipe/pipe_state_autogen.go
+++ b/pkg/tcpip/link/sharedmem/pipe/pipe_state_autogen.go
diff --git a/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe.go b/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe.go
index 62d17029e..62d17029e 100755..100644
--- a/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe.go
+++ b/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe.go
diff --git a/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe_state_autogen.go b/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe_state_autogen.go
index d3b40feb4..d3b40feb4 100755..100644
--- a/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe_state_autogen.go
+++ b/pkg/tcpip/link/sharedmem/pipe/pipe_unsafe_state_autogen.go
diff --git a/pkg/tcpip/link/sharedmem/pipe/rx.go b/pkg/tcpip/link/sharedmem/pipe/rx.go
index f22e533ac..f22e533ac 100755..100644
--- a/pkg/tcpip/link/sharedmem/pipe/rx.go
+++ b/pkg/tcpip/link/sharedmem/pipe/rx.go
diff --git a/pkg/tcpip/link/sharedmem/pipe/tx.go b/pkg/tcpip/link/sharedmem/pipe/tx.go
index 9841eb231..9841eb231 100755..100644
--- a/pkg/tcpip/link/sharedmem/pipe/tx.go
+++ b/pkg/tcpip/link/sharedmem/pipe/tx.go
diff --git a/pkg/tcpip/link/sharedmem/queue/queue_state_autogen.go b/pkg/tcpip/link/sharedmem/queue/queue_state_autogen.go
index 563d4fbb4..563d4fbb4 100755..100644
--- a/pkg/tcpip/link/sharedmem/queue/queue_state_autogen.go
+++ b/pkg/tcpip/link/sharedmem/queue/queue_state_autogen.go
diff --git a/pkg/tcpip/link/sharedmem/queue/rx.go b/pkg/tcpip/link/sharedmem/queue/rx.go
index 696e6c9e5..696e6c9e5 100755..100644
--- a/pkg/tcpip/link/sharedmem/queue/rx.go
+++ b/pkg/tcpip/link/sharedmem/queue/rx.go
diff --git a/pkg/tcpip/link/sharedmem/queue/tx.go b/pkg/tcpip/link/sharedmem/queue/tx.go
index beffe807b..beffe807b 100755..100644
--- a/pkg/tcpip/link/sharedmem/queue/tx.go
+++ b/pkg/tcpip/link/sharedmem/queue/tx.go
diff --git a/pkg/tcpip/link/sharedmem/rx.go b/pkg/tcpip/link/sharedmem/rx.go
index eec11e4cb..eec11e4cb 100755..100644
--- a/pkg/tcpip/link/sharedmem/rx.go
+++ b/pkg/tcpip/link/sharedmem/rx.go
diff --git a/pkg/tcpip/link/sharedmem/sharedmem.go b/pkg/tcpip/link/sharedmem/sharedmem.go
index 0796d717e..0796d717e 100755..100644
--- a/pkg/tcpip/link/sharedmem/sharedmem.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem.go
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_state_autogen.go b/pkg/tcpip/link/sharedmem/sharedmem_state_autogen.go
index bc12017b2..bc12017b2 100755..100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_state_autogen.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_state_autogen.go
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go b/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go
index f7e816a41..f7e816a41 100755..100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_unsafe.go
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_unsafe_state_autogen.go b/pkg/tcpip/link/sharedmem/sharedmem_unsafe_state_autogen.go
index ac3a66520..ac3a66520 100755..100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_unsafe_state_autogen.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_unsafe_state_autogen.go
diff --git a/pkg/tcpip/link/sharedmem/tx.go b/pkg/tcpip/link/sharedmem/tx.go
index 6b8d7859d..6b8d7859d 100755..100644
--- a/pkg/tcpip/link/sharedmem/tx.go
+++ b/pkg/tcpip/link/sharedmem/tx.go
diff --git a/pkg/tcpip/link/sniffer/sniffer_state_autogen.go b/pkg/tcpip/link/sniffer/sniffer_state_autogen.go
index 8d79defea..8d79defea 100755..100644
--- a/pkg/tcpip/link/sniffer/sniffer_state_autogen.go
+++ b/pkg/tcpip/link/sniffer/sniffer_state_autogen.go
diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
index 617446ea2..617446ea2 100755..100644
--- a/pkg/tcpip/link/tun/device.go
+++ b/pkg/tcpip/link/tun/device.go
diff --git a/pkg/tcpip/link/tun/protocol.go b/pkg/tcpip/link/tun/protocol.go
index 89d9d91a9..89d9d91a9 100755..100644
--- a/pkg/tcpip/link/tun/protocol.go
+++ b/pkg/tcpip/link/tun/protocol.go
diff --git a/pkg/tcpip/link/tun/tun_state_autogen.go b/pkg/tcpip/link/tun/tun_state_autogen.go
index 4b70647af..4b70647af 100755..100644
--- a/pkg/tcpip/link/tun/tun_state_autogen.go
+++ b/pkg/tcpip/link/tun/tun_state_autogen.go
diff --git a/pkg/tcpip/link/tun/tun_unsafe.go b/pkg/tcpip/link/tun/tun_unsafe.go
index 09ca9b527..09ca9b527 100755..100644
--- a/pkg/tcpip/link/tun/tun_unsafe.go
+++ b/pkg/tcpip/link/tun/tun_unsafe.go
diff --git a/pkg/tcpip/link/tun/tun_unsafe_state_autogen.go b/pkg/tcpip/link/tun/tun_unsafe_state_autogen.go
index 149299ea3..149299ea3 100755..100644
--- a/pkg/tcpip/link/tun/tun_unsafe_state_autogen.go
+++ b/pkg/tcpip/link/tun/tun_unsafe_state_autogen.go
diff --git a/pkg/tcpip/link/waitable/waitable.go b/pkg/tcpip/link/waitable/waitable.go
index 2b3741276..2b3741276 100755..100644
--- a/pkg/tcpip/link/waitable/waitable.go
+++ b/pkg/tcpip/link/waitable/waitable.go
diff --git a/pkg/tcpip/link/waitable/waitable_state_autogen.go b/pkg/tcpip/link/waitable/waitable_state_autogen.go
index 059424fa0..059424fa0 100755..100644
--- a/pkg/tcpip/link/waitable/waitable_state_autogen.go
+++ b/pkg/tcpip/link/waitable/waitable_state_autogen.go
diff --git a/pkg/tcpip/network/arp/arp_state_autogen.go b/pkg/tcpip/network/arp/arp_state_autogen.go
index 5cd8535e3..5cd8535e3 100755..100644
--- a/pkg/tcpip/network/arp/arp_state_autogen.go
+++ b/pkg/tcpip/network/arp/arp_state_autogen.go
diff --git a/pkg/tcpip/network/fragmentation/fragmentation_state_autogen.go b/pkg/tcpip/network/fragmentation/fragmentation_state_autogen.go
index cbaecdaa7..cbaecdaa7 100755..100644
--- a/pkg/tcpip/network/fragmentation/fragmentation_state_autogen.go
+++ b/pkg/tcpip/network/fragmentation/fragmentation_state_autogen.go
diff --git a/pkg/tcpip/network/fragmentation/reassembler_list.go b/pkg/tcpip/network/fragmentation/reassembler_list.go
index b5d40bd25..b5d40bd25 100755..100644
--- a/pkg/tcpip/network/fragmentation/reassembler_list.go
+++ b/pkg/tcpip/network/fragmentation/reassembler_list.go
diff --git a/pkg/tcpip/network/hash/hash_state_autogen.go b/pkg/tcpip/network/hash/hash_state_autogen.go
index 9467fe298..9467fe298 100755..100644
--- a/pkg/tcpip/network/hash/hash_state_autogen.go
+++ b/pkg/tcpip/network/hash/hash_state_autogen.go
diff --git a/pkg/tcpip/network/ipv4/ipv4_state_autogen.go b/pkg/tcpip/network/ipv4/ipv4_state_autogen.go
index 250b2128e..250b2128e 100755..100644
--- a/pkg/tcpip/network/ipv4/ipv4_state_autogen.go
+++ b/pkg/tcpip/network/ipv4/ipv4_state_autogen.go
diff --git a/pkg/tcpip/network/ipv6/ipv6_state_autogen.go b/pkg/tcpip/network/ipv6/ipv6_state_autogen.go
index 40c67d440..40c67d440 100755..100644
--- a/pkg/tcpip/network/ipv6/ipv6_state_autogen.go
+++ b/pkg/tcpip/network/ipv6/ipv6_state_autogen.go
diff --git a/pkg/tcpip/ports/ports_state_autogen.go b/pkg/tcpip/ports/ports_state_autogen.go
index f0ee1bb11..f0ee1bb11 100755..100644
--- a/pkg/tcpip/ports/ports_state_autogen.go
+++ b/pkg/tcpip/ports/ports_state_autogen.go
diff --git a/pkg/tcpip/seqnum/seqnum_state_autogen.go b/pkg/tcpip/seqnum/seqnum_state_autogen.go
index 23e79811d..23e79811d 100755..100644
--- a/pkg/tcpip/seqnum/seqnum_state_autogen.go
+++ b/pkg/tcpip/seqnum/seqnum_state_autogen.go
diff --git a/pkg/tcpip/stack/conntrack.go b/pkg/tcpip/stack/conntrack.go
index 7d1ede1f2..7d1ede1f2 100755..100644
--- a/pkg/tcpip/stack/conntrack.go
+++ b/pkg/tcpip/stack/conntrack.go
diff --git a/pkg/tcpip/stack/dhcpv6configurationfromndpra_string.go b/pkg/tcpip/stack/dhcpv6configurationfromndpra_string.go
index d199ded6a..d199ded6a 100755..100644
--- a/pkg/tcpip/stack/dhcpv6configurationfromndpra_string.go
+++ b/pkg/tcpip/stack/dhcpv6configurationfromndpra_string.go
diff --git a/pkg/tcpip/stack/forwarder.go b/pkg/tcpip/stack/forwarder.go
index 6b64cd37f..6b64cd37f 100755..100644
--- a/pkg/tcpip/stack/forwarder.go
+++ b/pkg/tcpip/stack/forwarder.go
diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.go
index 443423b3c..443423b3c 100755..100644
--- a/pkg/tcpip/stack/iptables.go
+++ b/pkg/tcpip/stack/iptables.go
diff --git a/pkg/tcpip/stack/iptables_targets.go b/pkg/tcpip/stack/iptables_targets.go
index 36cc6275d..36cc6275d 100755..100644
--- a/pkg/tcpip/stack/iptables_targets.go
+++ b/pkg/tcpip/stack/iptables_targets.go
diff --git a/pkg/tcpip/stack/iptables_types.go b/pkg/tcpip/stack/iptables_types.go
index fe06007ae..fe06007ae 100755..100644
--- a/pkg/tcpip/stack/iptables_types.go
+++ b/pkg/tcpip/stack/iptables_types.go
diff --git a/pkg/tcpip/stack/linkaddrentry_list.go b/pkg/tcpip/stack/linkaddrentry_list.go
index 43022f9b3..43022f9b3 100755..100644
--- a/pkg/tcpip/stack/linkaddrentry_list.go
+++ b/pkg/tcpip/stack/linkaddrentry_list.go
diff --git a/pkg/tcpip/stack/ndp.go b/pkg/tcpip/stack/ndp.go
index 526c7d6ff..526c7d6ff 100755..100644
--- a/pkg/tcpip/stack/ndp.go
+++ b/pkg/tcpip/stack/ndp.go
diff --git a/pkg/tcpip/stack/packet_buffer.go b/pkg/tcpip/stack/packet_buffer.go
index 926df4d7b..926df4d7b 100755..100644
--- a/pkg/tcpip/stack/packet_buffer.go
+++ b/pkg/tcpip/stack/packet_buffer.go
diff --git a/pkg/tcpip/stack/packet_buffer_list.go b/pkg/tcpip/stack/packet_buffer_list.go
index 460c74c5a..460c74c5a 100755..100644
--- a/pkg/tcpip/stack/packet_buffer_list.go
+++ b/pkg/tcpip/stack/packet_buffer_list.go
diff --git a/pkg/tcpip/stack/rand.go b/pkg/tcpip/stack/rand.go
index 421fb5c15..421fb5c15 100755..100644
--- a/pkg/tcpip/stack/rand.go
+++ b/pkg/tcpip/stack/rand.go
diff --git a/pkg/tcpip/stack/stack_state_autogen.go b/pkg/tcpip/stack/stack_state_autogen.go
index 6e98e8e95..6e98e8e95 100755..100644
--- a/pkg/tcpip/stack/stack_state_autogen.go
+++ b/pkg/tcpip/stack/stack_state_autogen.go
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index 45e930ad8..b7b227328 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -110,6 +110,71 @@ var (
 	ErrAddressFamilyNotSupported = &Error{msg: "address family not supported by protocol"}
 )
 
+var messageToError map[string]*Error
+
+var populate sync.Once
+
+// StringToError converts an error message to the error.
+func StringToError(s string) *Error {
+	populate.Do(func() {
+		var errors = []*Error{
+			ErrUnknownProtocol,
+			ErrUnknownNICID,
+			ErrUnknownDevice,
+			ErrUnknownProtocolOption,
+			ErrDuplicateNICID,
+			ErrDuplicateAddress,
+			ErrNoRoute,
+			ErrBadLinkEndpoint,
+			ErrAlreadyBound,
+			ErrInvalidEndpointState,
+			ErrAlreadyConnecting,
+			ErrAlreadyConnected,
+			ErrNoPortAvailable,
+			ErrPortInUse,
+			ErrBadLocalAddress,
+			ErrClosedForSend,
+			ErrClosedForReceive,
+			ErrWouldBlock,
+			ErrConnectionRefused,
+			ErrTimeout,
+			ErrAborted,
+			ErrConnectStarted,
+			ErrDestinationRequired,
+			ErrNotSupported,
+			ErrQueueSizeNotSupported,
+			ErrNotConnected,
+			ErrConnectionReset,
+			ErrConnectionAborted,
+			ErrNoSuchFile,
+			ErrInvalidOptionValue,
+			ErrNoLinkAddress,
+			ErrBadAddress,
+			ErrNetworkUnreachable,
+			ErrMessageTooLong,
+			ErrNoBufferSpace,
+			ErrBroadcastDisabled,
+			ErrNotPermitted,
+			ErrAddressFamilyNotSupported,
+		}
+
+		messageToError = make(map[string]*Error)
+		for _, e := range errors {
+			if messageToError[e.String()] != nil {
+				panic("tcpip errors with duplicated message: " + e.String())
+			}
+			messageToError[e.String()] = e
+		}
+	})
+
+	e, ok := messageToError[s]
+	if !ok {
+		panic("unknown error message: " + s)
+	}
+
+	return e
+}
+
 // Errors related to Subnet
 var (
 	errSubnetLengthMismatch = errors.New("subnet length of address and mask differ")
diff --git a/pkg/tcpip/tcpip_state_autogen.go b/pkg/tcpip/tcpip_state_autogen.go
index 8ea900688..8ea900688 100755..100644
--- a/pkg/tcpip/tcpip_state_autogen.go
+++ b/pkg/tcpip/tcpip_state_autogen.go
diff --git a/pkg/tcpip/tcpip_unsafe_state_autogen.go b/pkg/tcpip/tcpip_unsafe_state_autogen.go
index 32d2350f4..32d2350f4 100755..100644
--- a/pkg/tcpip/tcpip_unsafe_state_autogen.go
+++ b/pkg/tcpip/tcpip_unsafe_state_autogen.go
diff --git a/pkg/tcpip/timer.go b/pkg/tcpip/timer.go
index 59f3b391f..59f3b391f 100755..100644
--- a/pkg/tcpip/timer.go
+++ b/pkg/tcpip/timer.go
diff --git a/pkg/tcpip/transport/icmp/icmp_packet_list.go b/pkg/tcpip/transport/icmp/icmp_packet_list.go
index 42d63f976..42d63f976 100755..100644
--- a/pkg/tcpip/transport/icmp/icmp_packet_list.go
+++ b/pkg/tcpip/transport/icmp/icmp_packet_list.go
diff --git a/pkg/tcpip/transport/icmp/icmp_state_autogen.go b/pkg/tcpip/transport/icmp/icmp_state_autogen.go
index c26460a4b..c26460a4b 100755..100644
--- a/pkg/tcpip/transport/icmp/icmp_state_autogen.go
+++ b/pkg/tcpip/transport/icmp/icmp_state_autogen.go
diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index 23158173d..23158173d 100755..100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
diff --git a/pkg/tcpip/transport/packet/endpoint_state.go b/pkg/tcpip/transport/packet/endpoint_state.go
index 9b88f17e4..9b88f17e4 100755..100644
--- a/pkg/tcpip/transport/packet/endpoint_state.go
+++ b/pkg/tcpip/transport/packet/endpoint_state.go
diff --git a/pkg/tcpip/transport/packet/packet_list.go b/pkg/tcpip/transport/packet/packet_list.go
index 5231b066f..5231b066f 100755..100644
--- a/pkg/tcpip/transport/packet/packet_list.go
+++ b/pkg/tcpip/transport/packet/packet_list.go
diff --git a/pkg/tcpip/transport/packet/packet_state_autogen.go b/pkg/tcpip/transport/packet/packet_state_autogen.go
index 8ff339e08..8ff339e08 100755..100644
--- a/pkg/tcpip/transport/packet/packet_state_autogen.go
+++ b/pkg/tcpip/transport/packet/packet_state_autogen.go
diff --git a/pkg/tcpip/transport/raw/raw_packet_list.go b/pkg/tcpip/transport/raw/raw_packet_list.go
index 15a8c845b..15a8c845b 100755..100644
--- a/pkg/tcpip/transport/raw/raw_packet_list.go
+++ b/pkg/tcpip/transport/raw/raw_packet_list.go
diff --git a/pkg/tcpip/transport/raw/raw_state_autogen.go b/pkg/tcpip/transport/raw/raw_state_autogen.go
index c755fa847..c755fa847 100755..100644
--- a/pkg/tcpip/transport/raw/raw_state_autogen.go
+++ b/pkg/tcpip/transport/raw/raw_state_autogen.go
diff --git a/pkg/tcpip/transport/tcp/connect_unsafe.go b/pkg/tcpip/transport/tcp/connect_unsafe.go
index cfc304616..cfc304616 100755..100644
--- a/pkg/tcpip/transport/tcp/connect_unsafe.go
+++ b/pkg/tcpip/transport/tcp/connect_unsafe.go
diff --git a/pkg/tcpip/transport/tcp/dispatcher.go b/pkg/tcpip/transport/tcp/dispatcher.go
index 6062ca916..6062ca916 100755..100644
--- a/pkg/tcpip/transport/tcp/dispatcher.go
+++ b/pkg/tcpip/transport/tcp/dispatcher.go
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index 8b7562396..fc43c11e2 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -314,7 +314,7 @@ func (e *endpoint) loadLastError(s string) {
 		return
 	}
 
-	e.lastError = loadError(s)
+	e.lastError = tcpip.StringToError(s)
 }
 
 // saveHardError is invoked by stateify.
@@ -332,71 +332,7 @@ func (e *EndpointInfo) loadHardError(s string) {
 		return
 	}
 
-	e.HardError = loadError(s)
-}
-
-var messageToError map[string]*tcpip.Error
-
-var populate sync.Once
-
-func loadError(s string) *tcpip.Error {
-	populate.Do(func() {
-		var errors = []*tcpip.Error{
-			tcpip.ErrUnknownProtocol,
-			tcpip.ErrUnknownNICID,
-			tcpip.ErrUnknownDevice,
-			tcpip.ErrUnknownProtocolOption,
-			tcpip.ErrDuplicateNICID,
-			tcpip.ErrDuplicateAddress,
-			tcpip.ErrNoRoute,
-			tcpip.ErrBadLinkEndpoint,
-			tcpip.ErrAlreadyBound,
-			tcpip.ErrInvalidEndpointState,
-			tcpip.ErrAlreadyConnecting,
-			tcpip.ErrAlreadyConnected,
-			tcpip.ErrNoPortAvailable,
-			tcpip.ErrPortInUse,
-			tcpip.ErrBadLocalAddress,
-			tcpip.ErrClosedForSend,
-			tcpip.ErrClosedForReceive,
-			tcpip.ErrWouldBlock,
-			tcpip.ErrConnectionRefused,
-			tcpip.ErrTimeout,
-			tcpip.ErrAborted,
-			tcpip.ErrConnectStarted,
-			tcpip.ErrDestinationRequired,
-			tcpip.ErrNotSupported,
-			tcpip.ErrQueueSizeNotSupported,
-			tcpip.ErrNotConnected,
-			tcpip.ErrConnectionReset,
-			tcpip.ErrConnectionAborted,
-			tcpip.ErrNoSuchFile,
-			tcpip.ErrInvalidOptionValue,
-			tcpip.ErrNoLinkAddress,
-			tcpip.ErrBadAddress,
-			tcpip.ErrNetworkUnreachable,
-			tcpip.ErrMessageTooLong,
-			tcpip.ErrNoBufferSpace,
-			tcpip.ErrBroadcastDisabled,
-			tcpip.ErrNotPermitted,
-			tcpip.ErrAddressFamilyNotSupported,
-		}
-
-		messageToError = make(map[string]*tcpip.Error)
-		for _, e := range errors {
-			if messageToError[e.String()] != nil {
-				panic("tcpip errors with duplicated message: " + e.String())
-			}
-			messageToError[e.String()] = e
-		}
-	})
-
-	e, ok := messageToError[s]
-	if !ok {
-		panic("unknown error message: " + s)
-	}
-
-	return e
+	e.HardError = tcpip.StringToError(s)
 }
 
 // saveMeasureTime is invoked by stateify.
diff --git a/pkg/tcpip/transport/tcp/rcv_state.go b/pkg/tcpip/transport/tcp/rcv_state.go
index 2bf21a2e7..2bf21a2e7 100755..100644
--- a/pkg/tcpip/transport/tcp/rcv_state.go
+++ b/pkg/tcpip/transport/tcp/rcv_state.go
diff --git a/pkg/tcpip/transport/tcp/tcp_endpoint_list.go b/pkg/tcpip/transport/tcp/tcp_endpoint_list.go
index fb7046d8f..fb7046d8f 100755..100644
--- a/pkg/tcpip/transport/tcp/tcp_endpoint_list.go
+++ b/pkg/tcpip/transport/tcp/tcp_endpoint_list.go
diff --git a/pkg/tcpip/transport/tcp/tcp_segment_list.go b/pkg/tcpip/transport/tcp/tcp_segment_list.go
index 21638041c..21638041c 100755..100644
--- a/pkg/tcpip/transport/tcp/tcp_segment_list.go
+++ b/pkg/tcpip/transport/tcp/tcp_segment_list.go
diff --git a/pkg/tcpip/transport/tcp/tcp_state_autogen.go b/pkg/tcpip/transport/tcp/tcp_state_autogen.go
index e5d0a218a..e5d0a218a 100755..100644
--- a/pkg/tcpip/transport/tcp/tcp_state_autogen.go
+++ b/pkg/tcpip/transport/tcp/tcp_state_autogen.go
diff --git a/pkg/tcpip/transport/tcp/tcp_unsafe_state_autogen.go b/pkg/tcpip/transport/tcp/tcp_unsafe_state_autogen.go
index 4cb82fcc9..4cb82fcc9 100755..100644
--- a/pkg/tcpip/transport/tcp/tcp_unsafe_state_autogen.go
+++ b/pkg/tcpip/transport/tcp/tcp_unsafe_state_autogen.go
diff --git a/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go b/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go
index 12bc1b5b5..12bc1b5b5 100755..100644
--- a/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go
+++ b/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go
diff --git a/pkg/tcpip/transport/tcpconntrack/tcpconntrack_state_autogen.go b/pkg/tcpip/transport/tcpconntrack/tcpconntrack_state_autogen.go
index ff53204da..ff53204da 100755..100644
--- a/pkg/tcpip/transport/tcpconntrack/tcpconntrack_state_autogen.go
+++ b/pkg/tcpip/transport/tcpconntrack/tcpconntrack_state_autogen.go
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 756ab913a..647b2067a 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -106,6 +106,9 @@ type endpoint struct {
 	bindToDevice   tcpip.NICID
 	broadcast      bool
 
+	lastErrorMu sync.Mutex   `state:"nosave"`
+	lastError   *tcpip.Error `state:".(string)"`
+
 	// Values used to reserve a port or register a transport endpoint.
 	// (which ever happens first).
 	boundBindToDevice tcpip.NICID
@@ -188,6 +191,15 @@ func (e *endpoint) UniqueID() uint64 {
 	return e.uniqueID
 }
 
+func (e *endpoint) takeLastError() *tcpip.Error {
+	e.lastErrorMu.Lock()
+	defer e.lastErrorMu.Unlock()
+
+	err := e.lastError
+	e.lastError = nil
+	return err
+}
+
 // Abort implements stack.TransportEndpoint.Abort.
 func (e *endpoint) Abort() {
 	e.Close()
@@ -243,6 +255,10 @@ func (e *endpoint) IPTables() (stack.IPTables, error) {
 // Read reads data from the endpoint. This method does not block if
 // there is no data pending.
 func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
+	if err := e.takeLastError(); err != nil {
+		return buffer.View{}, tcpip.ControlMessages{}, err
+	}
+
 	e.rcvMu.Lock()
 
 	if e.rcvList.Empty() {
@@ -382,6 +398,10 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 }
 
 func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
+	if err := e.takeLastError(); err != nil {
+		return 0, nil, err
+	}
+
 	// MSG_MORE is unimplemented. (This also means that MSG_EOR is a no-op.)
 	if opts.More {
 		return 0, nil, tcpip.ErrInvalidOptionValue
@@ -853,6 +873,7 @@ func (e *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
 func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 	switch o := opt.(type) {
 	case tcpip.ErrorOption:
+		return e.takeLastError()
 	case *tcpip.MulticastInterfaceOption:
 		e.mu.Lock()
 		*o = tcpip.MulticastInterfaceOption{
@@ -1316,6 +1337,17 @@ func (e *endpoint) HandlePacket(r *stack.Route, id stack.TransportEndpointID, pk
 
 // HandleControlPacket implements stack.TransportEndpoint.HandleControlPacket.
 func (e *endpoint) HandleControlPacket(id stack.TransportEndpointID, typ stack.ControlType, extra uint32, pkt stack.PacketBuffer) {
+	if typ == stack.ControlPortUnreachable {
+		e.mu.RLock()
+		defer e.mu.RUnlock()
+
+		if e.state == StateConnected {
+			e.lastErrorMu.Lock()
+			defer e.lastErrorMu.Unlock()
+
+			e.lastError = tcpip.ErrConnectionRefused
+		}
+	}
 }
 
 // State implements tcpip.Endpoint.State.
diff --git a/pkg/tcpip/transport/udp/endpoint_state.go b/pkg/tcpip/transport/udp/endpoint_state.go
index 466bd9381..851e6b635 100644
--- a/pkg/tcpip/transport/udp/endpoint_state.go
+++ b/pkg/tcpip/transport/udp/endpoint_state.go
@@ -37,6 +37,24 @@ func (u *udpPacket) loadData(data buffer.VectorisedView) {
 	u.data = data
 }
 
+// saveLastError is invoked by stateify.
+func (e *endpoint) saveLastError() string {
+	if e.lastError == nil {
+		return ""
+	}
+
+	return e.lastError.String()
+}
+
+// loadLastError is invoked by stateify.
+func (e *endpoint) loadLastError(s string) {
+	if s == "" {
+		return
+	}
+
+	e.lastError = tcpip.StringToError(s)
+}
+
 // beforeSave is invoked by stateify.
 func (e *endpoint) beforeSave() {
 	// Stop incoming packets from being handled (and mutate endpoint state).
diff --git a/pkg/tcpip/transport/udp/udp_packet_list.go b/pkg/tcpip/transport/udp/udp_packet_list.go
index a6513e1e4..a6513e1e4 100755..100644
--- a/pkg/tcpip/transport/udp/udp_packet_list.go
+++ b/pkg/tcpip/transport/udp/udp_packet_list.go
diff --git a/pkg/tcpip/transport/udp/udp_state_autogen.go b/pkg/tcpip/transport/udp/udp_state_autogen.go
index e8ab82021..a6d58f290 100755..100644
--- a/pkg/tcpip/transport/udp/udp_state_autogen.go
+++ b/pkg/tcpip/transport/udp/udp_state_autogen.go
@@ -33,6 +33,8 @@ func (x *endpoint) save(m state.Map) {
 	x.beforeSave()
 	var rcvBufSizeMax int = x.saveRcvBufSizeMax()
 	m.SaveValue("rcvBufSizeMax", rcvBufSizeMax)
+	var lastError string = x.saveLastError()
+	m.SaveValue("lastError", lastError)
 	m.Save("TransportEndpointInfo", &x.TransportEndpointInfo)
 	m.Save("waiterQueue", &x.waiterQueue)
 	m.Save("uniqueID", &x.uniqueID)
@@ -95,6 +97,7 @@ func (x *endpoint) load(m state.Map) {
 	m.Load("effectiveNetProtos", &x.effectiveNetProtos)
 	m.Load("owner", &x.owner)
 	m.LoadValue("rcvBufSizeMax", new(int), func(y interface{}) { x.loadRcvBufSizeMax(y.(int)) })
+	m.LoadValue("lastError", new(string), func(y interface{}) { x.loadLastError(y.(string)) })
 	m.AfterLoad(x.afterLoad)
 }
 
diff --git a/pkg/unet/unet_state_autogen.go b/pkg/unet/unet_state_autogen.go
index 9bbf31d35..9bbf31d35 100755..100644
--- a/pkg/unet/unet_state_autogen.go
+++ b/pkg/unet/unet_state_autogen.go
diff --git a/pkg/unet/unet_unsafe_state_autogen.go b/pkg/unet/unet_unsafe_state_autogen.go
index 9bbf31d35..9bbf31d35 100755..100644
--- a/pkg/unet/unet_unsafe_state_autogen.go
+++ b/pkg/unet/unet_unsafe_state_autogen.go
diff --git a/pkg/urpc/urpc_state_autogen.go b/pkg/urpc/urpc_state_autogen.go
index 5fdca6717..5fdca6717 100755..100644
--- a/pkg/urpc/urpc_state_autogen.go
+++ b/pkg/urpc/urpc_state_autogen.go
diff --git a/pkg/usermem/access_type.go b/pkg/usermem/access_type.go
index 9c1742a59..9c1742a59 100755..100644
--- a/pkg/usermem/access_type.go
+++ b/pkg/usermem/access_type.go
diff --git a/pkg/usermem/addr.go b/pkg/usermem/addr.go
index e79210804..c4100481e 100755..100644
--- a/pkg/usermem/addr.go
+++ b/pkg/usermem/addr.go
@@ -106,3 +106,20 @@ func (ar AddrRange) IsPageAligned() bool {
 func (ar AddrRange) String() string {
 	return fmt.Sprintf("[%#x, %#x)", ar.Start, ar.End)
 }
+
+// PageRoundDown/Up are equivalent to Addr.RoundDown/Up, but without the
+// potentially truncating conversion from uint64 to Addr. This is necessary
+// because there is no way to define generic "PageRoundDown/Up" functions in Go.
+
+// PageRoundDown returns x rounded down to the nearest page boundary.
+func PageRoundDown(x uint64) uint64 {
+	return x &^ (PageSize - 1)
+}
+
+// PageRoundUp returns x rounded up to the nearest page boundary.
+// ok is true iff rounding up did not wrap around.
+func PageRoundUp(x uint64) (addr uint64, ok bool) {
+	addr = PageRoundDown(x + PageSize - 1)
+	ok = addr >= x
+	return
+}
diff --git a/pkg/usermem/addr_range.go b/pkg/usermem/addr_range.go
index 152ed1434..152ed1434 100755..100644
--- a/pkg/usermem/addr_range.go
+++ b/pkg/usermem/addr_range.go
diff --git a/pkg/usermem/addr_range_seq_unsafe.go b/pkg/usermem/addr_range_seq_unsafe.go
index c09337c15..c09337c15 100755..100644
--- a/pkg/usermem/addr_range_seq_unsafe.go
+++ b/pkg/usermem/addr_range_seq_unsafe.go
diff --git a/pkg/usermem/bytes_io.go b/pkg/usermem/bytes_io.go
index e177d30eb..e177d30eb 100755..100644
--- a/pkg/usermem/bytes_io.go
+++ b/pkg/usermem/bytes_io.go
diff --git a/pkg/usermem/bytes_io_unsafe.go b/pkg/usermem/bytes_io_unsafe.go
index 20de5037d..20de5037d 100755..100644
--- a/pkg/usermem/bytes_io_unsafe.go
+++ b/pkg/usermem/bytes_io_unsafe.go
diff --git a/pkg/usermem/usermem.go b/pkg/usermem/usermem.go
index cd6a0ea6b..cd6a0ea6b 100755..100644
--- a/pkg/usermem/usermem.go
+++ b/pkg/usermem/usermem.go
diff --git a/pkg/usermem/usermem_arm64.go b/pkg/usermem/usermem_arm64.go
index fdfc30a66..fdfc30a66 100755..100644
--- a/pkg/usermem/usermem_arm64.go
+++ b/pkg/usermem/usermem_arm64.go
diff --git a/pkg/usermem/usermem_arm64_state_autogen.go b/pkg/usermem/usermem_arm64_state_autogen.go
index d7c365e5d..d7c365e5d 100755..100644
--- a/pkg/usermem/usermem_arm64_state_autogen.go
+++ b/pkg/usermem/usermem_arm64_state_autogen.go
diff --git a/pkg/usermem/usermem_state_autogen.go b/pkg/usermem/usermem_state_autogen.go
index 20aa2d2de..20aa2d2de 100755..100644
--- a/pkg/usermem/usermem_state_autogen.go
+++ b/pkg/usermem/usermem_state_autogen.go
diff --git a/pkg/usermem/usermem_unsafe_state_autogen.go b/pkg/usermem/usermem_unsafe_state_autogen.go
index 62f8af4c9..62f8af4c9 100755..100644
--- a/pkg/usermem/usermem_unsafe_state_autogen.go
+++ b/pkg/usermem/usermem_unsafe_state_autogen.go
diff --git a/pkg/usermem/usermem_x86.go b/pkg/usermem/usermem_x86.go
index d96f829fb..d96f829fb 100755..100644
--- a/pkg/usermem/usermem_x86.go
+++ b/pkg/usermem/usermem_x86.go
diff --git a/pkg/usermem/usermem_x86_state_autogen.go b/pkg/usermem/usermem_x86_state_autogen.go
index cca386593..cca386593 100755..100644
--- a/pkg/usermem/usermem_x86_state_autogen.go
+++ b/pkg/usermem/usermem_x86_state_autogen.go
diff --git a/pkg/waiter/waiter_list.go b/pkg/waiter/waiter_list.go
index 35431f5a4..35431f5a4 100755..100644
--- a/pkg/waiter/waiter_list.go
+++ b/pkg/waiter/waiter_list.go
diff --git a/pkg/waiter/waiter_state_autogen.go b/pkg/waiter/waiter_state_autogen.go
index cf7f5fc2c..cf7f5fc2c 100755..100644
--- a/pkg/waiter/waiter_state_autogen.go
+++ b/pkg/waiter/waiter_state_autogen.go