6 files changed, 38 insertions, 6 deletions
diff --git a/pkg/tcpip/transport/tcp/BUILD b/pkg/tcpip/transport/tcp/BUILD
index 18ff89ffc..e860ee484 100644
--- a/pkg/tcpip/transport/tcp/BUILD
+++ b/pkg/tcpip/transport/tcp/BUILD
@@ -49,6 +49,7 @@ go_library(
         "segment_heap.go",
         "segment_queue.go",
         "segment_state.go",
+        "segment_unsafe.go",
         "snd.go",
         "snd_state.go",
         "tcp_endpoint_list.go",
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index b34e47bbd..5d6174a59 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -49,7 +49,7 @@ const (
 
 	// DefaultReceiveBufferSize is the default size of the receive buffer
 	// for an endpoint.
-	DefaultReceiveBufferSize = 1 << 20 // 1MB
+	DefaultReceiveBufferSize = 32 << 10 // 32KB
 
 	// MaxBufferSize is the largest size a receive/send buffer can grow to.
 	MaxBufferSize = 4 << 20 // 4MB
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index dd89a292a..5e0bfe585 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -372,7 +372,7 @@ func (r *receiver) handleRcvdSegment(s *segment) (drop bool, err *tcpip.Error) {
 			// We only store the segment if it's within our buffer
 			// size limit.
 			if r.pendingBufUsed < r.pendingBufSize {
-				r.pendingBufUsed += s.logicalLen()
+				r.pendingBufUsed += seqnum.Size(s.segMemSize())
 				s.incRef()
 				heap.Push(&r.pendingRcvdSegments, s)
 				UpdateSACKBlocks(&r.ep.sack, segSeq, segSeq.Add(segLen), r.rcvNxt)
@@ -406,7 +406,7 @@ func (r *receiver) handleRcvdSegment(s *segment) (drop bool, err *tcpip.Error) {
 		}
 
 		heap.Pop(&r.pendingRcvdSegments)
-		r.pendingBufUsed -= s.logicalLen()
+		r.pendingBufUsed -= seqnum.Size(s.segMemSize())
 		s.decRef()
 	}
 	return false, nil
diff --git a/pkg/tcpip/transport/tcp/segment.go b/pkg/tcpip/transport/tcp/segment.go
index 0280892a8..bb60dc29d 100644
--- a/pkg/tcpip/transport/tcp/segment.go
+++ b/pkg/tcpip/transport/tcp/segment.go
@@ -138,6 +138,12 @@ func (s *segment) logicalLen() seqnum.Size {
 	return l
 }
 
+// segMemSize is the amount of memory used to hold the segment data and
+// the associated metadata.
+func (s *segment) segMemSize() int {
+	return segSize + s.data.Size()
+}
+
 // parse populates the sequence & ack numbers, flags, and window fields of the
 // segment from the TCP header stored in the data. It then updates the view to
 // skip the header.
diff --git a/pkg/tcpip/transport/tcp/segment_unsafe.go b/pkg/tcpip/transport/tcp/segment_unsafe.go
new file mode 100644
index 000000000..0ab7b8f56
--- /dev/null
+++ b/pkg/tcpip/transport/tcp/segment_unsafe.go
@@ -0,0 +1,23 @@
+// 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 tcp
+
+import (
+	"unsafe"
+)
+
+const (
+	segSize = int(unsafe.Sizeof(segment{}))
+)
diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 06fde2a79..37e7767d6 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -143,12 +143,14 @@ func New(t *testing.T, mtu uint32) *Context {
 		TransportProtocols: []stack.TransportProtocol{tcp.NewProtocol()},
 	})
 
+	const sendBufferSize = 1 << 20 // 1 MiB
+	const recvBufferSize = 1 << 20 // 1 MiB
 	// Allow minimum send/receive buffer sizes to be 1 during tests.
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.SendBufferSizeOption{Min: 1, Default: tcp.DefaultSendBufferSize, Max: 10 * tcp.DefaultSendBufferSize}); err != nil {
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.SendBufferSizeOption{Min: 1, Default: sendBufferSize, Max: 10 * sendBufferSize}); err != nil {
 		t.Fatalf("SetTransportProtocolOption failed: %s", err)
 	}
 
-	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.ReceiveBufferSizeOption{Min: 1, Default: tcp.DefaultReceiveBufferSize, Max: 10 * tcp.DefaultReceiveBufferSize}); err != nil {
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.ReceiveBufferSizeOption{Min: 1, Default: recvBufferSize, Max: 10 * recvBufferSize}); err != nil {
 		t.Fatalf("SetTransportProtocolOption failed: %s", err)
 	}
 
@@ -202,7 +204,7 @@ func New(t *testing.T, mtu uint32) *Context {
 		t:           t,
 		s:           s,
 		linkEP:      ep,
-		WindowScale: uint8(tcp.FindWndScale(tcp.DefaultReceiveBufferSize)),
+		WindowScale: uint8(tcp.FindWndScale(recvBufferSize)),
 	}
 }