zstd: Tweak decoder allocs.

zstd/blockdec.go

@@ -232,7 +232,7 @@ func (b *blockDec) decodeBuf(hist *history) error {
 			if b.lowMem {
 				b.dst = make([]byte, b.RLESize)
 			} else {
-				b.dst = make([]byte, maxBlockSize)
+				b.dst = make([]byte, maxCompressedBlockSize)
 			}
 		}
 		b.dst = b.dst[:b.RLESize]

zstd/decoder.go

@@ -770,7 +770,7 @@ func (d *Decoder) startStreamDecoder(ctx context.Context, r io.Reader, output ch
 					if block.lowMem {
 						block.dst = make([]byte, block.RLESize)
 					} else {
-						block.dst = make([]byte, maxBlockSize)
+						block.dst = make([]byte, maxCompressedBlockSize)
 					}
 				}
 				block.dst = block.dst[:block.RLESize]

zstd/decoder_test.go

@@ -1249,7 +1249,7 @@ func BenchmarkDecoder_DecoderReset(b *testing.B) {
 	defer dec.Close()
 	bench := func(name string, b *testing.B, opts []DOption, in, want []byte) {
 		b.Helper()
-		buf := &bytesReader{Reader: bytes.NewReader(in), buf: in}
+		buf := newBytesReader(in)
 		dec, err := NewReader(nil, opts...)
 		if err != nil {
 			b.Fatal(err)
@@ -1298,6 +1298,11 @@ func BenchmarkDecoder_DecoderReset(b *testing.B) {
 	}
 }
 
+// newBytesReader returns a *bytes.Reader that also supports Bytes() []byte
+func newBytesReader(b []byte) *bytesReader {
+	return &bytesReader{Reader: bytes.NewReader(b), buf: b}
+}
+
 type bytesReader struct {
 	*bytes.Reader
 	buf []byte
@@ -1328,7 +1333,7 @@ func BenchmarkDecoder_DecoderNewNoRead(b *testing.B) {
 	bench := func(name string, b *testing.B, opts []DOption, in, want []byte) {
 		b.Helper()
 		b.Run(name, func(b *testing.B) {
-			buf := &bytesReader{Reader: bytes.NewReader(in), buf: in}
+			buf := newBytesReader(in)
 			b.SetBytes(1)
 			b.ReportAllocs()
 			b.ResetTimer()
@@ -1372,6 +1377,60 @@ func BenchmarkDecoder_DecoderNewNoRead(b *testing.B) {
 	}
 }
 
+func BenchmarkDecoder_DecoderNewSomeRead(b *testing.B) {
+	var buf [1 << 20]byte
+	bench := func(name string, b *testing.B, opts []DOption, in *os.File) {
+		b.Helper()
+		b.Run(name, func(b *testing.B) {
+			//b.ReportAllocs()
+			b.ResetTimer()
+			var heapTotal int64
+			var m runtime.MemStats
+			for i := 0; i < b.N; i++ {
+				runtime.GC()
+				runtime.ReadMemStats(&m)
+				heapTotal -= int64(m.HeapInuse)
+				_, err := in.Seek(io.SeekStart, 0)
+				if err != nil {
+					b.Fatal(err)
+				}
+
+				dec, err := NewReader(in, opts...)
+				if err != nil {
+					b.Fatal(err)
+				}
+				// Read 16 MB
+				_, err = io.CopyBuffer(io.Discard, io.LimitReader(dec, 16<<20), buf[:])
+				if err != nil {
+					b.Fatal(err)
+				}
+				runtime.GC()
+				runtime.ReadMemStats(&m)
+				heapTotal += int64(m.HeapInuse)
+
+				dec.Close()
+			}
+			b.ReportMetric(float64(heapTotal)/float64(b.N), "b/op")
+		})
+	}
+	files := []string{"testdata/000002.map.win32K.zst", "testdata/000002.map.win1MB.zst", "testdata/000002.map.win8MB.zst"}
+	for _, file := range files {
+		if !strings.HasSuffix(file, ".zst") {
+			continue
+		}
+		r, err := os.Open(file)
+		if err != nil {
+			b.Fatal(err)
+		}
+		defer r.Close()
+
+		b.Run(file, func(b *testing.B) {
+			bench("stream-single", b, []DOption{WithDecodeBuffersBelow(0), WithDecoderConcurrency(1)}, r)
+			bench("stream-single-himem", b, []DOption{WithDecodeBuffersBelow(0), WithDecoderConcurrency(1), WithDecoderLowmem(false)}, r)
+		})
+	}
+}
+
 func BenchmarkDecoder_DecodeAll(b *testing.B) {
 	zr := testCreateZipReader("testdata/benchdecoder.zip", b)
 	dec, err := NewReader(nil, WithDecoderConcurrency(1))

zstd/enc_fast.go

@@ -304,7 +304,7 @@ func (e *fastEncoder) EncodeNoHist(blk *blockEnc, src []byte) {
 		minNonLiteralBlockSize = 1 + 1 + inputMargin
 	)
 	if debugEncoder {
-		if len(src) > maxBlockSize {
+		if len(src) > maxCompressedBlockSize {
 			panic("src too big")
 		}
 	}

zstd/framedec.go

@@ -261,11 +261,16 @@ func (d *frameDec) reset(br byteBuffer) error {
 	}
 	d.history.windowSize = int(d.WindowSize)
 	if !d.o.lowMem || d.history.windowSize < maxBlockSize {
-		// Alloc 2x window size if not low-mem, or very small window size.
+		// Alloc 2x window size if not low-mem, or window size below 2MB.
 		d.history.allocFrameBuffer = d.history.windowSize * 2
 	} else {
-		// Alloc with one additional block
-		d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize
+		if d.o.lowMem {
+			// Alloc with 1MB extra.
+			d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize/2
+		} else {
+			// Alloc with 2MB extra.
+			d.history.allocFrameBuffer = d.history.windowSize + maxBlockSize
+		}
 	}
 
 	if debugDecoder {

zstd/fuzz_test.go

@@ -50,7 +50,7 @@ func FuzzDecodeAll(f *testing.F) {
 	})
 }
 
-func FuzzDecodeAllNoBMI2(f *testing.F) {
+func FuzzDecAllNoBMI2(f *testing.F) {
 	if !cpuinfo.HasBMI2() {
 		f.Skip("No BMI, so already tested")
 		return
@@ -62,18 +62,20 @@ func FuzzDecodeAllNoBMI2(f *testing.F) {
 func FuzzDecoder(f *testing.F) {
 	fuzz.AddFromZip(f, "testdata/fuzz/decode-corpus-raw.zip", true, testing.Short())
 	fuzz.AddFromZip(f, "testdata/fuzz/decode-corpus-encoded.zip", false, testing.Short())
-	decLow, err := NewReader(nil, WithDecoderLowmem(true), WithDecoderConcurrency(2), WithDecoderMaxMemory(20<<20), WithDecoderMaxWindow(1<<20), IgnoreChecksum(true))
+	decLow, err := NewReader(nil, WithDecoderLowmem(true), WithDecoderConcurrency(2), WithDecoderMaxMemory(20<<20), WithDecoderMaxWindow(1<<20), IgnoreChecksum(true), WithDecodeBuffersBelow(8<<10))
 	if err != nil {
 		f.Fatal(err)
 	}
 	defer decLow.Close()
 	// Test with high memory, but sync decoding
-	decHi, err := NewReader(nil, WithDecoderLowmem(false), WithDecoderConcurrency(1), WithDecoderMaxMemory(20<<20), WithDecoderMaxWindow(1<<20), IgnoreChecksum(true))
+	decHi, err := NewReader(nil, WithDecoderLowmem(false), WithDecoderConcurrency(1), WithDecoderMaxMemory(20<<20), WithDecoderMaxWindow(1<<20), IgnoreChecksum(true), WithDecodeBuffersBelow(8<<10))
 	if err != nil {
 		f.Fatal(err)
 	}
 	defer decHi.Close()
 
+	brLow := newBytesReader(nil)
+	brHi := newBytesReader(nil)
 	f.Fuzz(func(t *testing.T, b []byte) {
 		// Just test if we crash...
 		defer func() {
@@ -82,11 +84,13 @@ func FuzzDecoder(f *testing.F) {
 				t.Fatal(r)
 			}
 		}()
-		err := decLow.Reset(io.NopCloser(bytes.NewReader(b)))
+		brLow.Reset(b)
+		brHi.Reset(b)
+		err := decLow.Reset(brLow)
 		if err != nil {
 			t.Fatal(err)
 		}
-		err = decHi.Reset(io.NopCloser(bytes.NewReader(b)))
+		err = decHi.Reset(brHi)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -104,6 +108,15 @@ func FuzzDecoder(f *testing.F) {
 	})
 }
 
+func FuzzNoBMI2Dec(f *testing.F) {
+	if !cpuinfo.HasBMI2() {
+		f.Skip("No BMI, so already tested")
+		return
+	}
+	defer cpuinfo.DisableBMI2()()
+	FuzzDecoder(f)
+}
+
 func FuzzEncoding(f *testing.F) {
 	fuzz.AddFromZip(f, "testdata/fuzz/encode-corpus-raw.zip", true, testing.Short())
 	fuzz.AddFromZip(f, "testdata/comp-crashers.zip", true, false)