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perf: Optimize dirInode prevDirListingTimeStamp by using atomic.Int64 instead of time.Time #4862

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Merged
vedantdas-source merged 2 commits into from
Jul 18, 2026
+74 −29
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perf: Optimize dirInode prevDirListingTimeStamp by using atomic.Int64 instead of time.Time #4862

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fac8f05
perf: changed dirInode prevDirListingTimeStamp to atomic.Int64
vedantdas-source Jul 10, 2026
4db3346
added test to check concurrency bug
vedantdas-source Jul 10, 2026
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27 changes: 19 additions & 8 deletions internal/fs/inode/dir.go
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Original file line number Diff line number Diff line change
Expand Up @@ -265,7 +265,7 @@ type dirInode struct {
// (via kernel) the directory listing from the filesystem.
// Specially used when kernelListCacheTTL > 0 that means kernel list-cache is
// enabled.
prevDirListingTimeStamp time.Time
prevDirListingTimeStamp atomic.Int64
Comment thread
vedantdas-source marked this conversation as resolved.

metadataCacheTtlSecs int64

Expand Down Expand Up @@ -634,7 +634,6 @@ func (d *dirInode) CancelCurrDirPrefetcher() {
if d.prefetcher != nil {
d.prefetcher.Cancel()
}
return
}

// UpdateSize is a no-op for implicit directories. These directories are not
Expand Down Expand Up @@ -1105,7 +1104,12 @@ func (d *dirInode) ReadEntryCores(ctx context.Context, tok string) (cores map[Na
return
}

d.prevDirListingTimeStamp = d.cacheClock.Now()
if now := d.cacheClock.Now(); !now.IsZero() {
d.prevDirListingTimeStamp.Store(now.UnixNano())
} else {
d.prevDirListingTimeStamp.Store(0)
}

return
}

Expand Down Expand Up @@ -1508,12 +1512,19 @@ func (d *dirInode) LocalFileEntries(localFileInodes map[Name]Inode) (localEntrie
func (d *dirInode) ShouldInvalidateKernelListCache(ttl time.Duration) bool {
// prevDirListingTimeStamp.IsZero() true means listing has not happened yet, and we should
// invalidate for clean start.
if d.prevDirListingTimeStamp.IsZero() {
prevNS := d.prevDirListingTimeStamp.Load()
if prevNS == 0 {
return true
}

cachedDuration := d.cacheClock.Now().Sub(d.prevDirListingTimeStamp)
return cachedDuration >= ttl
now := d.cacheClock.Now()
if now.IsZero() {
return true
}
nowNS := now.UnixNano()
if nowNS < prevNS {
return true
}
return time.Duration(nowNS-prevNS) >= ttl
}

// LOCKS_REQUIRED(d)
Expand Down Expand Up @@ -1571,7 +1582,7 @@ func (d *dirInode) RenameFolder(ctx context.Context, folderName string, destinat

func (d *dirInode) InvalidateKernelListCache() {
// Set prevDirListingTimeStamp to Zero time so that cache is invalidated.
d.prevDirListingTimeStamp = time.Time{}
d.prevDirListingTimeStamp.Store(0)
}

func (d *dirInode) isBucketHierarchical() bool {
Expand Down
76 changes: 55 additions & 21 deletions internal/fs/inode/dir_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ import (
"os"
"path"
"sort"
"sync"
"testing"
"time"

Expand Down Expand Up @@ -933,13 +934,13 @@ func (t *DirTest) TestReadDescendants_NonEmpty() {
func (t *DirTest) TestReadEntries_Empty() {
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())
entries, err := t.readAllEntries()

require.NoError(t.T(), err)
assert.ElementsMatch(t.T(), []fuseutil.Dirent{}, entries)
// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestReadEntries_NonEmpty_ImplicitDirsDisabled() {
Expand All @@ -966,7 +967,7 @@ func (t *DirTest) TestReadEntries_NonEmpty_ImplicitDirsDisabled() {
// Nil prevDirListingTimeStamp
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())

// Read entries.
entries, err := t.readAllEntries()
Expand Down Expand Up @@ -1003,7 +1004,7 @@ func (t *DirTest) TestReadEntries_NonEmpty_ImplicitDirsDisabled() {
}

// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestReadEntries_NonEmpty_ImplicitDirsEnabled() {
Expand Down Expand Up @@ -1033,7 +1034,7 @@ func (t *DirTest) TestReadEntries_NonEmpty_ImplicitDirsEnabled() {
// Nil prevDirListingTimeStamp
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())

// Read entries.
entries, err := t.readAllEntries()
Expand Down Expand Up @@ -1077,7 +1078,7 @@ func (t *DirTest) TestReadEntries_NonEmpty_ImplicitDirsEnabled() {
}

// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestReadEntries_TypeCaching() {
Expand All @@ -1097,7 +1098,7 @@ func (t *DirTest) TestReadEntries_TypeCaching() {
// Nil prevDirListingTimeStamp
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())

// Read the directory, priming the type cache.
_, err = t.readAllEntries()
Expand Down Expand Up @@ -1136,21 +1137,21 @@ func (t *DirTest) TestReadEntries_TypeCaching() {
assert.Equal(t.T(), dirObjName, result.MinObject.Name)

// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestReadEntryCores_Empty() {
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())

cores, unsupportedPaths, err := t.readAllEntryCores()

require.NoError(t.T(), err)
assert.Equal(t.T(), 0, len(cores))
assert.Equal(t.T(), 0, len(unsupportedPaths))
// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestReadEntryCores_NonEmpty_ImplicitDirsDisabled() {
Expand Down Expand Up @@ -1184,7 +1185,7 @@ func (t *DirTest) TestReadEntryCores_NonEmpty_ImplicitDirsDisabled() {
// Nil prevDirListingTimeStamp
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())

// Read cores.
cores, _, _, err = t.in.ReadEntryCores(t.ctx, "")
Expand All @@ -1196,7 +1197,7 @@ func (t *DirTest) TestReadEntryCores_NonEmpty_ImplicitDirsDisabled() {
t.validateCore(cores, "file", false, metadata.RegularFileType, testFileName)
t.validateCore(cores, "symlink", false, metadata.SymlinkType, symlinkName)
// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestReadEntryCores_NonEmpty_ImplicitDirsEnabled() {
Expand Down Expand Up @@ -1238,7 +1239,7 @@ func (t *DirTest) TestReadEntryCores_NonEmpty_ImplicitDirsEnabled() {
// Nil prevDirListingTimeStamp
d := t.in.(*dirInode)
require.NotNil(t.T(), d)
require.True(t.T(), d.prevDirListingTimeStamp.IsZero())
require.Zero(t.T(), d.prevDirListingTimeStamp.Load())

// Read cores.
cores, unsupportedPaths, err = t.readAllEntryCores()
Expand All @@ -1253,7 +1254,7 @@ func (t *DirTest) TestReadEntryCores_NonEmpty_ImplicitDirsEnabled() {
t.validateCore(cores, "symlink", false, metadata.SymlinkType, symlinkName)
assert.ElementsMatch(t.T(), []string{dirInodeName + "../", dirInodeName + "/"}, unsupportedPaths)
// Make sure prevDirListingTimeStamp is initialized.
require.False(t.T(), d.prevDirListingTimeStamp.IsZero())
require.NotZero(t.T(), d.prevDirListingTimeStamp.Load())
}

func (t *DirTest) TestCreateChildFile_DoesntExist() {
Expand Down Expand Up @@ -2023,7 +2024,7 @@ func (t *DirTest) TestLocalFileEntriesWithUnlinkedLocalChildFiles() {

func (t *DirTest) Test_ShouldInvalidateKernelListCache_ListingNotHappenedYet() {
d := t.in.(*dirInode)
d.prevDirListingTimeStamp = time.Time{}
d.prevDirListingTimeStamp.Store(0)

// Irrespective of the ttl value, this should always return true.
shouldInvalidate := t.in.ShouldInvalidateKernelListCache(util.MaxTimeDuration)
Expand All @@ -2033,7 +2034,7 @@ func (t *DirTest) Test_ShouldInvalidateKernelListCache_ListingNotHappenedYet() {

func (t *DirTest) Test_ShouldInvalidateKernelListCache_WithinTtl() {
d := t.in.(*dirInode)
d.prevDirListingTimeStamp = d.cacheClock.Now()
d.prevDirListingTimeStamp.Store(d.cacheClock.Now().UnixNano())
ttl := time.Second * 10
t.clock.AdvanceTime(ttl / 2)

Expand All @@ -2044,7 +2045,7 @@ func (t *DirTest) Test_ShouldInvalidateKernelListCache_WithinTtl() {

func (t *DirTest) Test_ShouldInvalidateKernelListCache_ExpiredTtl() {
d := t.in.(*dirInode)
d.prevDirListingTimeStamp = d.cacheClock.Now()
d.prevDirListingTimeStamp.Store(d.cacheClock.Now().UnixNano())
ttl := 10 * time.Second
t.clock.AdvanceTime(ttl + time.Second)

Expand All @@ -2055,7 +2056,7 @@ func (t *DirTest) Test_ShouldInvalidateKernelListCache_ExpiredTtl() {

func (t *DirTest) Test_ShouldInvalidateKernelListCache_ZeroTtl() {
d := t.in.(*dirInode)
d.prevDirListingTimeStamp = d.cacheClock.Now()
d.prevDirListingTimeStamp.Store(d.cacheClock.Now().UnixNano())
ttl := time.Duration(0)

shouldInvalidate := t.in.ShouldInvalidateKernelListCache(ttl)
Expand All @@ -2065,12 +2066,12 @@ func (t *DirTest) Test_ShouldInvalidateKernelListCache_ZeroTtl() {

func (t *DirTest) Test_InvalidateKernelListCache() {
d := t.in.(*dirInode)
d.prevDirListingTimeStamp = d.cacheClock.Now()
assert.False(t.T(), d.prevDirListingTimeStamp.IsZero())
d.prevDirListingTimeStamp.Store(d.cacheClock.Now().UnixNano())
assert.False(t.T(), d.prevDirListingTimeStamp.Load() == 0)

t.in.InvalidateKernelListCache()

assert.True(t.T(), d.prevDirListingTimeStamp.IsZero())
assert.True(t.T(), d.prevDirListingTimeStamp.Load() == 0)
}

func (t *DirTest) Test_ReadObjectsUnlocked() {
Expand Down Expand Up @@ -2402,3 +2403,36 @@ func (t *DirTest) TestMetadataPrefetcher_InitializationGuards() {
})
}
}

func (t *DirTest) Test_ShouldInvalidateKernelListCache_RaceCondition() {
Comment thread
vedantdas-source marked this conversation as resolved.
// This test demonstrates the concurrency data race that existed when using time.Time.
// If run with `go test -race`, it would fail prior to the atomic.Int64 refactor.
var wg sync.WaitGroup
wg.Add(3)

go func() {
defer wg.Done()
for range 1000 {
t.in.InvalidateKernelListCache()
}
}()

go func() {
defer wg.Done()
for range 1000 {
// Simulate concurrent lock-free reads
_ = t.in.ShouldInvalidateKernelListCache(time.Second)
}
}()

go func() {
defer wg.Done()
d := t.in.(*dirInode)
for range 1000 {
// Simulate concurrent writes (like what ReadEntryCores does)
d.prevDirListingTimeStamp.Store(d.cacheClock.Now().UnixNano())
}
}()

wg.Wait()
}
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