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-rw-r--r--pkg/sentry/pgalloc/BUILD22
-rw-r--r--pkg/sentry/pgalloc/pgalloc.go215
-rw-r--r--pkg/sentry/pgalloc/pgalloc_test.go198
3 files changed, 270 insertions, 165 deletions
diff --git a/pkg/sentry/pgalloc/BUILD b/pkg/sentry/pgalloc/BUILD
index 1eeb9f317..a9836ba71 100644
--- a/pkg/sentry/pgalloc/BUILD
+++ b/pkg/sentry/pgalloc/BUILD
@@ -33,6 +33,7 @@ go_template_instance(
out = "usage_set.go",
consts = {
"minDegree": "10",
+ "trackGaps": "1",
},
imports = {
"platform": "gvisor.dev/gvisor/pkg/sentry/platform",
@@ -48,6 +49,26 @@ go_template_instance(
},
)
+go_template_instance(
+ name = "reclaim_set",
+ out = "reclaim_set.go",
+ consts = {
+ "minDegree": "10",
+ },
+ imports = {
+ "platform": "gvisor.dev/gvisor/pkg/sentry/platform",
+ },
+ package = "pgalloc",
+ prefix = "reclaim",
+ template = "//pkg/segment:generic_set",
+ types = {
+ "Key": "uint64",
+ "Range": "platform.FileRange",
+ "Value": "reclaimSetValue",
+ "Functions": "reclaimSetFunctions",
+ },
+)
+
go_library(
name = "pgalloc",
srcs = [
@@ -56,6 +77,7 @@ go_library(
"evictable_range_set.go",
"pgalloc.go",
"pgalloc_unsafe.go",
+ "reclaim_set.go",
"save_restore.go",
"usage_set.go",
],
diff --git a/pkg/sentry/pgalloc/pgalloc.go b/pkg/sentry/pgalloc/pgalloc.go
index 2b11ea4ae..c8d9facc2 100644
--- a/pkg/sentry/pgalloc/pgalloc.go
+++ b/pkg/sentry/pgalloc/pgalloc.go
@@ -108,12 +108,6 @@ type MemoryFile struct {
usageSwapped uint64
usageLast time.Time
- // minUnallocatedPage is the minimum page that may be unallocated.
- // i.e., there are no unallocated pages below minUnallocatedPage.
- //
- // minUnallocatedPage is protected by mu.
- minUnallocatedPage uint64
-
// fileSize is the size of the backing memory file in bytes. fileSize is
// always a power-of-two multiple of chunkSize.
//
@@ -146,11 +140,9 @@ type MemoryFile struct {
// is protected by mu.
reclaimable bool
- // minReclaimablePage is the minimum page that may be reclaimable.
- // i.e., all reclaimable pages are >= minReclaimablePage.
- //
- // minReclaimablePage is protected by mu.
- minReclaimablePage uint64
+ // relcaim is the collection of regions for reclaim. relcaim is protected
+ // by mu.
+ reclaim reclaimSet
// reclaimCond is signaled (with mu locked) when reclaimable or destroyed
// transitions from false to true.
@@ -273,12 +265,10 @@ type evictableMemoryUserInfo struct {
}
const (
- chunkShift = 24
- chunkSize = 1 << chunkShift // 16 MB
+ chunkShift = 30
+ chunkSize = 1 << chunkShift // 1 GB
chunkMask = chunkSize - 1
- initialSize = chunkSize
-
// maxPage is the highest 64-bit page.
maxPage = math.MaxUint64 &^ (usermem.PageSize - 1)
)
@@ -302,19 +292,12 @@ func NewMemoryFile(file *os.File, opts MemoryFileOpts) (*MemoryFile, error) {
if err := file.Truncate(0); err != nil {
return nil, err
}
- if err := file.Truncate(initialSize); err != nil {
- return nil, err
- }
f := &MemoryFile{
- opts: opts,
- fileSize: initialSize,
- file: file,
- // No pages are reclaimable. DecRef will always be able to
- // decrease minReclaimablePage from this point.
- minReclaimablePage: maxPage,
- evictable: make(map[EvictableMemoryUser]*evictableMemoryUserInfo),
+ opts: opts,
+ file: file,
+ evictable: make(map[EvictableMemoryUser]*evictableMemoryUserInfo),
}
- f.mappings.Store(make([]uintptr, initialSize/chunkSize))
+ f.mappings.Store(make([]uintptr, 0))
f.reclaimCond.L = &f.mu
if f.opts.DelayedEviction == DelayedEvictionEnabled && f.opts.UseHostMemcgPressure {
@@ -404,39 +387,28 @@ func (f *MemoryFile) Allocate(length uint64, kind usage.MemoryKind) (platform.Fi
alignment = usermem.HugePageSize
}
- start, minUnallocatedPage := findUnallocatedRange(&f.usage, f.minUnallocatedPage, length, alignment)
- end := start + length
- // File offsets are int64s. Since length must be strictly positive, end
- // cannot legitimately be 0.
- if end < start || int64(end) <= 0 {
+ // Find a range in the underlying file.
+ fr, ok := findAvailableRange(&f.usage, f.fileSize, length, alignment)
+ if !ok {
return platform.FileRange{}, syserror.ENOMEM
}
- // Expand the file if needed. Double the file size on each expansion;
- // uncommitted pages have effectively no cost.
- fileSize := f.fileSize
- for int64(end) > fileSize {
- if fileSize >= 2*fileSize {
- // fileSize overflow.
- return platform.FileRange{}, syserror.ENOMEM
- }
- fileSize *= 2
- }
- if fileSize > f.fileSize {
- if err := f.file.Truncate(fileSize); err != nil {
+ // Expand the file if needed. Note that findAvailableRange will
+ // appropriately double the fileSize when required.
+ if int64(fr.End) > f.fileSize {
+ if err := f.file.Truncate(int64(fr.End)); err != nil {
return platform.FileRange{}, err
}
- f.fileSize = fileSize
+ f.fileSize = int64(fr.End)
f.mappingsMu.Lock()
oldMappings := f.mappings.Load().([]uintptr)
- newMappings := make([]uintptr, fileSize>>chunkShift)
+ newMappings := make([]uintptr, f.fileSize>>chunkShift)
copy(newMappings, oldMappings)
f.mappings.Store(newMappings)
f.mappingsMu.Unlock()
}
// Mark selected pages as in use.
- fr := platform.FileRange{start, end}
if f.opts.ManualZeroing {
if err := f.forEachMappingSlice(fr, func(bs []byte) {
for i := range bs {
@@ -453,49 +425,71 @@ func (f *MemoryFile) Allocate(length uint64, kind usage.MemoryKind) (platform.Fi
panic(fmt.Sprintf("allocating %v: failed to insert into usage set:\n%v", fr, &f.usage))
}
- if minUnallocatedPage < start {
- f.minUnallocatedPage = minUnallocatedPage
- } else {
- // start was the first unallocated page. The next must be
- // somewhere beyond end.
- f.minUnallocatedPage = end
- }
-
return fr, nil
}
-// findUnallocatedRange returns the first unallocated page in usage of the
-// specified length and alignment beginning at page start and the first single
-// unallocated page.
-func findUnallocatedRange(usage *usageSet, start, length, alignment uint64) (uint64, uint64) {
- // Only searched until the first page is found.
- firstPage := start
- foundFirstPage := false
- alignMask := alignment - 1
- for seg := usage.LowerBoundSegment(start); seg.Ok(); seg = seg.NextSegment() {
- r := seg.Range()
+// findAvailableRange returns an available range in the usageSet.
+//
+// Note that scanning for available slots takes place from end first backwards,
+// then forwards. This heuristic has important consequence for how sequential
+// mappings can be merged in the host VMAs, given that addresses for both
+// application and sentry mappings are allocated top-down (from higher to
+// lower addresses). The file is also grown expoentially in order to create
+// space for mappings to be allocated downwards.
+//
+// Precondition: alignment must be a power of 2.
+func findAvailableRange(usage *usageSet, fileSize int64, length, alignment uint64) (platform.FileRange, bool) {
+ alignmentMask := alignment - 1
+ for gap := usage.UpperBoundGap(uint64(fileSize)); gap.Ok(); gap = gap.PrevLargeEnoughGap(length) {
+ // Start searching only at end of file.
+ end := gap.End()
+ if end > uint64(fileSize) {
+ end = uint64(fileSize)
+ }
- if !foundFirstPage && r.Start > firstPage {
- foundFirstPage = true
+ // Start at the top and align downwards.
+ start := end - length
+ if start > end {
+ break // Underflow.
}
+ start &^= alignmentMask
- if start >= r.End {
- // start was rounded up to an alignment boundary from the end
- // of a previous segment and is now beyond r.End.
+ // Is the gap still sufficient?
+ if start < gap.Start() {
continue
}
- // This segment represents allocated or reclaimable pages; only the
- // range from start to the segment's beginning is allocatable, and the
- // next allocatable range begins after the segment.
- if r.Start > start && r.Start-start >= length {
- break
+
+ // Allocate in the given gap.
+ return platform.FileRange{start, start + length}, true
+ }
+
+ // Check that it's possible to fit this allocation at the end of a file of any size.
+ min := usage.LastGap().Start()
+ min = (min + alignmentMask) &^ alignmentMask
+ if min+length < min {
+ // Overflow.
+ return platform.FileRange{}, false
+ }
+
+ // Determine the minimum file size required to fit this allocation at its end.
+ for {
+ if fileSize >= 2*fileSize {
+ // Is this because it's initially empty?
+ if fileSize == 0 {
+ fileSize += chunkSize
+ } else {
+ // fileSize overflow.
+ return platform.FileRange{}, false
+ }
+ } else {
+ // Double the current fileSize.
+ fileSize *= 2
}
- start = (r.End + alignMask) &^ alignMask
- if !foundFirstPage {
- firstPage = r.End
+ start := (uint64(fileSize) - length) &^ alignmentMask
+ if start >= min {
+ return platform.FileRange{start, start + length}, true
}
}
- return start, firstPage
}
// AllocateAndFill allocates memory of the given kind and fills it by calling
@@ -616,6 +610,7 @@ func (f *MemoryFile) DecRef(fr platform.FileRange) {
}
val.refs--
if val.refs == 0 {
+ f.reclaim.Add(seg.Range(), reclaimSetValue{})
freed = true
// Reclassify memory as System, until it's freed by the reclaim
// goroutine.
@@ -628,10 +623,6 @@ func (f *MemoryFile) DecRef(fr platform.FileRange) {
f.usage.MergeAdjacent(fr)
if freed {
- if fr.Start < f.minReclaimablePage {
- // We've freed at least one lower page.
- f.minReclaimablePage = fr.Start
- }
f.reclaimable = true
f.reclaimCond.Signal()
}
@@ -1030,6 +1021,7 @@ func (f *MemoryFile) String() string {
// for allocation.
func (f *MemoryFile) runReclaim() {
for {
+ // N.B. We must call f.markReclaimed on the returned FrameRange.
fr, ok := f.findReclaimable()
if !ok {
break
@@ -1085,6 +1077,10 @@ func (f *MemoryFile) runReclaim() {
}
}
+// findReclaimable finds memory that has been marked for reclaim.
+//
+// Note that there returned range will be removed from tracking. It
+// must be reclaimed (removed from f.usage) at this point.
func (f *MemoryFile) findReclaimable() (platform.FileRange, bool) {
f.mu.Lock()
defer f.mu.Unlock()
@@ -1103,18 +1099,15 @@ func (f *MemoryFile) findReclaimable() (platform.FileRange, bool) {
}
f.reclaimCond.Wait()
}
- // Allocate returns the first usable range in offset order and is
- // currently a linear scan, so reclaiming from the beginning of the
- // file minimizes the expected latency of Allocate.
- for seg := f.usage.LowerBoundSegment(f.minReclaimablePage); seg.Ok(); seg = seg.NextSegment() {
- if seg.ValuePtr().refs == 0 {
- f.minReclaimablePage = seg.End()
- return seg.Range(), true
- }
+ // Allocate works from the back of the file inwards, so reclaim
+ // preserves this order to minimize the cost of the search.
+ if seg := f.reclaim.LastSegment(); seg.Ok() {
+ fr := seg.Range()
+ f.reclaim.Remove(seg)
+ return fr, true
}
- // No pages are reclaimable.
+ // Nothing is reclaimable.
f.reclaimable = false
- f.minReclaimablePage = maxPage
}
}
@@ -1122,8 +1115,8 @@ func (f *MemoryFile) markReclaimed(fr platform.FileRange) {
f.mu.Lock()
defer f.mu.Unlock()
seg := f.usage.FindSegment(fr.Start)
- // All of fr should be mapped to a single uncommitted reclaimable segment
- // accounted to System.
+ // All of fr should be mapped to a single uncommitted reclaimable
+ // segment accounted to System.
if !seg.Ok() {
panic(fmt.Sprintf("reclaimed pages %v include unreferenced pages:\n%v", fr, &f.usage))
}
@@ -1137,14 +1130,10 @@ func (f *MemoryFile) markReclaimed(fr platform.FileRange) {
}); got != want {
panic(fmt.Sprintf("reclaimed pages %v in segment %v has incorrect state %v, wanted %v:\n%v", fr, seg.Range(), got, want, &f.usage))
}
- // Deallocate reclaimed pages. Even though all of seg is reclaimable, the
- // caller of markReclaimed may not have decommitted it, so we can only mark
- // fr as reclaimed.
+ // Deallocate reclaimed pages. Even though all of seg is reclaimable,
+ // the caller of markReclaimed may not have decommitted it, so we can
+ // only mark fr as reclaimed.
f.usage.Remove(f.usage.Isolate(seg, fr))
- if fr.Start < f.minUnallocatedPage {
- // We've deallocated at least one lower page.
- f.minUnallocatedPage = fr.Start
- }
}
// StartEvictions requests that f evict all evictable allocations. It does not
@@ -1255,3 +1244,27 @@ func (evictableRangeSetFunctions) Merge(_ EvictableRange, _ evictableRangeSetVal
func (evictableRangeSetFunctions) Split(_ EvictableRange, _ evictableRangeSetValue, _ uint64) (evictableRangeSetValue, evictableRangeSetValue) {
return evictableRangeSetValue{}, evictableRangeSetValue{}
}
+
+// reclaimSetValue is the value type of reclaimSet.
+type reclaimSetValue struct{}
+
+type reclaimSetFunctions struct{}
+
+func (reclaimSetFunctions) MinKey() uint64 {
+ return 0
+}
+
+func (reclaimSetFunctions) MaxKey() uint64 {
+ return math.MaxUint64
+}
+
+func (reclaimSetFunctions) ClearValue(val *reclaimSetValue) {
+}
+
+func (reclaimSetFunctions) Merge(_ platform.FileRange, _ reclaimSetValue, _ platform.FileRange, _ reclaimSetValue) (reclaimSetValue, bool) {
+ return reclaimSetValue{}, true
+}
+
+func (reclaimSetFunctions) Split(_ platform.FileRange, _ reclaimSetValue, _ uint64) (reclaimSetValue, reclaimSetValue) {
+ return reclaimSetValue{}, reclaimSetValue{}
+}
diff --git a/pkg/sentry/pgalloc/pgalloc_test.go b/pkg/sentry/pgalloc/pgalloc_test.go
index 293f22c6b..b5b68eb52 100644
--- a/pkg/sentry/pgalloc/pgalloc_test.go
+++ b/pkg/sentry/pgalloc/pgalloc_test.go
@@ -23,39 +23,49 @@ import (
const (
page = usermem.PageSize
hugepage = usermem.HugePageSize
+ topPage = (1 << 63) - page
)
func TestFindUnallocatedRange(t *testing.T) {
for _, test := range []struct {
- desc string
- usage *usageSegmentDataSlices
- start uint64
- length uint64
- alignment uint64
- unallocated uint64
- minUnallocated uint64
+ desc string
+ usage *usageSegmentDataSlices
+ fileSize int64
+ length uint64
+ alignment uint64
+ start uint64
+ expectFail bool
}{
{
- desc: "Initial allocation succeeds",
- usage: &usageSegmentDataSlices{},
- start: 0,
- length: page,
- alignment: page,
- unallocated: 0,
- minUnallocated: 0,
+ desc: "Initial allocation succeeds",
+ usage: &usageSegmentDataSlices{},
+ length: page,
+ alignment: page,
+ start: chunkSize - page, // Grows by chunkSize, allocate down.
},
{
- desc: "Allocation begins at start of file",
+ desc: "Allocation finds empty space at start of file",
usage: &usageSegmentDataSlices{
Start: []uint64{page},
End: []uint64{2 * page},
Values: []usageInfo{{refs: 1}},
},
- start: 0,
- length: page,
- alignment: page,
- unallocated: 0,
- minUnallocated: 0,
+ fileSize: 2 * page,
+ length: page,
+ alignment: page,
+ start: 0,
+ },
+ {
+ desc: "Allocation finds empty space at end of file",
+ usage: &usageSegmentDataSlices{
+ Start: []uint64{0},
+ End: []uint64{page},
+ Values: []usageInfo{{refs: 1}},
+ },
+ fileSize: 2 * page,
+ length: page,
+ alignment: page,
+ start: page,
},
{
desc: "In-use frames are not allocatable",
@@ -64,11 +74,10 @@ func TestFindUnallocatedRange(t *testing.T) {
End: []uint64{page, 2 * page},
Values: []usageInfo{{refs: 1}, {refs: 2}},
},
- start: 0,
- length: page,
- alignment: page,
- unallocated: 2 * page,
- minUnallocated: 2 * page,
+ fileSize: 2 * page,
+ length: page,
+ alignment: page,
+ start: 3 * page, // Double fileSize, allocate top-down.
},
{
desc: "Reclaimable frames are not allocatable",
@@ -77,11 +86,10 @@ func TestFindUnallocatedRange(t *testing.T) {
End: []uint64{page, 2 * page, 3 * page},
Values: []usageInfo{{refs: 1}, {refs: 0}, {refs: 1}},
},
- start: 0,
- length: page,
- alignment: page,
- unallocated: 3 * page,
- minUnallocated: 3 * page,
+ fileSize: 3 * page,
+ length: page,
+ alignment: page,
+ start: 5 * page, // Double fileSize, grow down.
},
{
desc: "Gaps between in-use frames are allocatable",
@@ -90,11 +98,10 @@ func TestFindUnallocatedRange(t *testing.T) {
End: []uint64{page, 3 * page},
Values: []usageInfo{{refs: 1}, {refs: 1}},
},
- start: 0,
- length: page,
- alignment: page,
- unallocated: page,
- minUnallocated: page,
+ fileSize: 3 * page,
+ length: page,
+ alignment: page,
+ start: page,
},
{
desc: "Inadequately-sized gaps are rejected",
@@ -103,14 +110,13 @@ func TestFindUnallocatedRange(t *testing.T) {
End: []uint64{page, 3 * page},
Values: []usageInfo{{refs: 1}, {refs: 1}},
},
- start: 0,
- length: 2 * page,
- alignment: page,
- unallocated: 3 * page,
- minUnallocated: page,
+ fileSize: 3 * page,
+ length: 2 * page,
+ alignment: page,
+ start: 4 * page, // Double fileSize, grow down.
},
{
- desc: "Hugepage alignment is honored",
+ desc: "Alignment is honored at end of file",
usage: &usageSegmentDataSlices{
Start: []uint64{0, hugepage + page},
// Hugepage-sized gap here that shouldn't be allocated from
@@ -118,37 +124,95 @@ func TestFindUnallocatedRange(t *testing.T) {
End: []uint64{page, hugepage + 2*page},
Values: []usageInfo{{refs: 1}, {refs: 1}},
},
- start: 0,
- length: hugepage,
- alignment: hugepage,
- unallocated: 2 * hugepage,
- minUnallocated: page,
+ fileSize: hugepage + 2*page,
+ length: hugepage,
+ alignment: hugepage,
+ start: 3 * hugepage, // Double fileSize until alignment is satisfied, grow down.
+ },
+ {
+ desc: "Alignment is honored before end of file",
+ usage: &usageSegmentDataSlices{
+ Start: []uint64{0, 2*hugepage + page},
+ // Page will need to be shifted down from top.
+ End: []uint64{page, 2*hugepage + 2*page},
+ Values: []usageInfo{{refs: 1}, {refs: 1}},
+ },
+ fileSize: 2*hugepage + 2*page,
+ length: hugepage,
+ alignment: hugepage,
+ start: hugepage,
},
{
- desc: "Pages before start ignored",
+ desc: "Allocations are compact if possible",
usage: &usageSegmentDataSlices{
Start: []uint64{page, 3 * page},
End: []uint64{2 * page, 4 * page},
Values: []usageInfo{{refs: 1}, {refs: 2}},
},
- start: page,
- length: page,
- alignment: page,
- unallocated: 2 * page,
- minUnallocated: 2 * page,
+ fileSize: 4 * page,
+ length: page,
+ alignment: page,
+ start: 2 * page,
+ },
+ {
+ desc: "Top-down allocation within one gap",
+ usage: &usageSegmentDataSlices{
+ Start: []uint64{page, 4 * page, 7 * page},
+ End: []uint64{2 * page, 5 * page, 8 * page},
+ Values: []usageInfo{{refs: 1}, {refs: 2}, {refs: 1}},
+ },
+ fileSize: 8 * page,
+ length: page,
+ alignment: page,
+ start: 6 * page,
+ },
+ {
+ desc: "Top-down allocation between multiple gaps",
+ usage: &usageSegmentDataSlices{
+ Start: []uint64{page, 3 * page, 5 * page},
+ End: []uint64{2 * page, 4 * page, 6 * page},
+ Values: []usageInfo{{refs: 1}, {refs: 2}, {refs: 1}},
+ },
+ fileSize: 6 * page,
+ length: page,
+ alignment: page,
+ start: 4 * page,
},
{
- desc: "start may be in the middle of segment",
+ desc: "Top-down allocation with large top gap",
usage: &usageSegmentDataSlices{
- Start: []uint64{0, 3 * page},
+ Start: []uint64{page, 3 * page},
End: []uint64{2 * page, 4 * page},
Values: []usageInfo{{refs: 1}, {refs: 2}},
},
- start: page,
- length: page,
- alignment: page,
- unallocated: 2 * page,
- minUnallocated: 2 * page,
+ fileSize: 8 * page,
+ length: page,
+ alignment: page,
+ start: 7 * page,
+ },
+ {
+ desc: "Gaps found with possible overflow",
+ usage: &usageSegmentDataSlices{
+ Start: []uint64{page, topPage - page},
+ End: []uint64{2 * page, topPage},
+ Values: []usageInfo{{refs: 1}, {refs: 1}},
+ },
+ fileSize: topPage,
+ length: page,
+ alignment: page,
+ start: topPage - 2*page,
+ },
+ {
+ desc: "Overflow detected",
+ usage: &usageSegmentDataSlices{
+ Start: []uint64{page},
+ End: []uint64{topPage},
+ Values: []usageInfo{{refs: 1}},
+ },
+ fileSize: topPage,
+ length: 2 * page,
+ alignment: page,
+ expectFail: true,
},
} {
t.Run(test.desc, func(t *testing.T) {
@@ -156,12 +220,18 @@ func TestFindUnallocatedRange(t *testing.T) {
if err := usage.ImportSortedSlices(test.usage); err != nil {
t.Fatalf("Failed to initialize usage from %v: %v", test.usage, err)
}
- unallocated, minUnallocated := findUnallocatedRange(&usage, test.start, test.length, test.alignment)
- if unallocated != test.unallocated {
- t.Errorf("findUnallocatedRange(%v, %x, %x, %x): got unallocated %x, wanted %x", test.usage, test.start, test.length, test.alignment, unallocated, test.unallocated)
+ fr, ok := findAvailableRange(&usage, test.fileSize, test.length, test.alignment)
+ if !test.expectFail && !ok {
+ t.Fatalf("findAvailableRange(%v, %x, %x, %x): got %x, false wanted %x, true", test.usage, test.fileSize, test.length, test.alignment, fr.Start, test.start)
+ }
+ if test.expectFail && ok {
+ t.Fatalf("findAvailableRange(%v, %x, %x, %x): got %x, true wanted %x, false", test.usage, test.fileSize, test.length, test.alignment, fr.Start, test.start)
+ }
+ if ok && fr.Start != test.start {
+ t.Errorf("findAvailableRange(%v, %x, %x, %x): got start=%x, wanted %x", test.usage, test.fileSize, test.length, test.alignment, fr.Start, test.start)
}
- if minUnallocated != test.minUnallocated {
- t.Errorf("findUnallocatedRange(%v, %x, %x, %x): got minUnallocated %x, wanted %x", test.usage, test.start, test.length, test.alignment, minUnallocated, test.minUnallocated)
+ if ok && fr.End != test.start+test.length {
+ t.Errorf("findAvailableRange(%v, %x, %x, %x): got end=%x, wanted %x", test.usage, test.fileSize, test.length, test.alignment, fr.End, test.start+test.length)
}
})
}