Sentry: always use "best speed" compression for save and remove the option.

PiperOrigin-RevId: 195835861
Change-Id: Ib696b1b571a6b061725a33c535cd7215fe518b97

pkg/sentry/state/state.go

@@ -50,11 +50,6 @@ type SaveOpts struct {
 	// Metadata is save metadata.
 	Metadata map[string]string
 
-	// CompressionLevel is the compression level to use.
-	//
-	// See statefile.NewWriter for details.
-	CompressionLevel int
-
 	// Callback is called prior to unpause, with any save error.
 	Callback func(err error)
 }
@@ -76,7 +71,7 @@ func (opts SaveOpts) Save(k *kernel.Kernel, w *watchdog.Watchdog) error {
 	addSaveMetadata(opts.Metadata)
 
 	// Open the statefile.
-	wc, err := statefile.NewWriter(opts.Destination, opts.Key, opts.Metadata, opts.CompressionLevel)
+	wc, err := statefile.NewWriter(opts.Destination, opts.Key, opts.Metadata)
 	if err != nil {
 		err = ErrStateFile{err}
 	} else {

pkg/state/statefile/statefile.go

@@ -45,6 +45,7 @@ package statefile
 
 import (
 	"bytes"
+	"compress/flate"
 	"crypto/hmac"
 	"crypto/sha256"
 	"encoding/json"
@@ -86,7 +87,7 @@ var ErrMetadataInvalid = fmt.Errorf("metadata invalid, can't start with _")
 // NewWriter returns a state data writer for a statefile.
 //
 // Note that the returned WriteCloser must be closed.
-func NewWriter(w io.Writer, key []byte, metadata map[string]string, compressionLevel int) (io.WriteCloser, error) {
+func NewWriter(w io.Writer, key []byte, metadata map[string]string) (io.WriteCloser, error) {
 	if metadata == nil {
 		metadata = make(map[string]string)
 	}
@@ -140,8 +141,11 @@ func NewWriter(w io.Writer, key []byte, metadata map[string]string, compressionL
 
 	w = hashio.NewWriter(w, h)
 
-	// Wrap in compression.
-	return compressio.NewWriter(w, compressionChunkSize, compressionLevel)
+	// Wrap in compression. We always use "best speed" mode here. When using
+	// "best compression" mode, there is usually only a little gain in file
+	// size reduction, which translate to even smaller gain in restore
+	// latency reduction, while inccuring much more CPU usage at save time.
+	return compressio.NewWriter(w, compressionChunkSize, flate.BestSpeed)
 }
 
 // MetadataUnsafe reads out the metadata from a state file without verifying any

pkg/state/statefile/statefile_test.go

@@ -16,7 +16,6 @@ package statefile
 
 import (
 	"bytes"
-	"compress/flate"
 	crand "crypto/rand"
 	"encoding/base64"
 	"io"
@@ -89,7 +88,7 @@ func TestStatefile(t *testing.T) {
 					var bufDecoded bytes.Buffer
 
 					// Do all the writing.
-					w, err := NewWriter(&bufEncoded, key, c.metadata, flate.BestSpeed)
+					w, err := NewWriter(&bufEncoded, key, c.metadata)
 					if err != nil {
 						t.Fatalf("error creating writer: got %v, expected nil", err)
 					}
@@ -195,7 +194,7 @@ func benchmark(b *testing.B, size int, write bool, compressible bool) {
 	var stateBuf bytes.Buffer
 	writeState := func() {
 		stateBuf.Reset()
-		w, err := NewWriter(&stateBuf, key, nil, flate.BestSpeed)
+		w, err := NewWriter(&stateBuf, key, nil)
 		if err != nil {
 			b.Fatalf("error creating writer: %v", err)
 		}