storage: don't buffer tar split file in memory

I cannot see any reason why we should buffer the full tar split content
in memory before writing it. That layer is still mark partial at this
point and the store is locked so there is no concurrent access either
thus we do not need the atomic rename here.

Signed-off-by: Paul Holzinger <[email protected]>

Author: Luap99

storage/layers.go

@@ -31,6 +31,7 @@ import (
 	"go.podman.io/storage/pkg/ioutils"
 	"go.podman.io/storage/pkg/lockfile"
 	"go.podman.io/storage/pkg/mount"
+	"go.podman.io/storage/pkg/pools"
 	"go.podman.io/storage/pkg/stringid"
 	"go.podman.io/storage/pkg/system"
 	"go.podman.io/storage/pkg/tarlog"
@@ -2398,6 +2399,13 @@ func (r *layerStore) ApplyDiff(to string, diff io.Reader) (size int64, err error
 	return r.applyDiffWithOptions(to, nil, diff)
 }
 
+func createTarSplitFile(r *layerStore, layerID string) (*os.File, error) {
+	if err := os.MkdirAll(filepath.Dir(r.tspath(layerID)), 0o700); err != nil {
+		return nil, err
+	}
+	return os.OpenFile(r.tspath(layerID), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
+}
+
 // Requires startWriting.
 func (r *layerStore) applyDiffWithOptions(to string, layerOptions *LayerOptions, diff io.Reader) (size int64, err error) {
 	if !r.lockfile.IsReadWrite() {
@@ -2442,13 +2450,19 @@ func (r *layerStore) applyDiffWithOptions(to string, layerOptions *LayerOptions,
 	compressedCounter := ioutils.NewWriteCounter(compressedWriter)
 	defragmented = io.TeeReader(defragmented, compressedCounter)
 
-	tsdata := bytes.Buffer{}
+	tarSplitFile, err := createTarSplitFile(r, layer.ID)
+	if err != nil {
+		return -1, err
+	}
+	defer tarSplitFile.Close()
+	tarSplitWriter := pools.BufioWriter32KPool.Get(tarSplitFile)
+
 	uidLog := make(map[uint32]struct{})
 	gidLog := make(map[uint32]struct{})
 	var uncompressedCounter *ioutils.WriteCounter
 
 	size, err = func() (int64, error) { // A scope for defer
-		compressor, err := pgzip.NewWriterLevel(&tsdata, pgzip.BestSpeed)
+		compressor, err := pgzip.NewWriterLevel(tarSplitWriter, pgzip.BestSpeed)
 		if err != nil {
 			return -1, err
 		}
@@ -2496,12 +2510,13 @@ func (r *layerStore) applyDiffWithOptions(to string, layerOptions *LayerOptions,
 		return -1, err
 	}
 
-	if err := os.MkdirAll(filepath.Dir(r.tspath(layer.ID)), 0o700); err != nil {
-		return -1, err
+	if err := tarSplitWriter.Flush(); err != nil {
+		return -1, fmt.Errorf("failed to flush tar split writer buffer: %w", err)
 	}
-	if err := ioutils.AtomicWriteFile(r.tspath(layer.ID), tsdata.Bytes(), 0o600); err != nil {
-		return -1, err
+	if err := tarSplitFile.Sync(); err != nil {
+		return -1, fmt.Errorf("sync tar split file: %w", err)
 	}
+
 	if compressedDigester != nil {
 		compressedDigest = compressedDigester.Digest()
 	}
@@ -2597,10 +2612,16 @@ func (r *layerStore) applyDiffFromStagingDirectory(id string, diffOutput *driver
 	}
 
 	if diffOutput.TarSplit != nil {
-		tsdata := bytes.Buffer{}
-		compressor, err := pgzip.NewWriterLevel(&tsdata, pgzip.BestSpeed)
+		tarSplitFile, err := createTarSplitFile(r, layer.ID)
 		if err != nil {
-			compressor = pgzip.NewWriter(&tsdata)
+			return err
+		}
+		defer tarSplitFile.Close()
+		tarSplitWriter := pools.BufioWriter32KPool.Get(tarSplitFile)
+
+		compressor, err := pgzip.NewWriterLevel(tarSplitWriter, pgzip.BestSpeed)
+		if err != nil {
+			compressor = pgzip.NewWriter(tarSplitWriter)
 		}
 		if _, err := diffOutput.TarSplit.Seek(0, io.SeekStart); err != nil {
 			return err
@@ -2614,11 +2635,12 @@ func (r *layerStore) applyDiffFromStagingDirectory(id string, diffOutput *driver
 			return err
 		}
 		compressor.Close()
-		if err := os.MkdirAll(filepath.Dir(r.tspath(layer.ID)), 0o700); err != nil {
-			return err
+
+		if err := tarSplitWriter.Flush(); err != nil {
+			return fmt.Errorf("failed to flush tar split writer buffer: %w", err)
 		}
-		if err := ioutils.AtomicWriteFile(r.tspath(layer.ID), tsdata.Bytes(), 0o600); err != nil {
-			return err
+		if err := tarSplitFile.Sync(); err != nil {
+			return fmt.Errorf("sync tar split file: %w", err)
 		}
 	}
 	for k, v := range diffOutput.BigData {