daemon/logger: Increase initial buffers size

Make the allocated buffers bigger to allow better reusability and avoid
frequent reallocations.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

daemon/logger/jsonfilelog/jsonfilelog.go

@@ -23,7 +23,7 @@ const Name = "json-file"
 // Every buffer will have to store the same constant json structure with the message
 // len(`{"log":"","stream:"stdout","time":"2000-01-01T00:00:00.000000000Z"}\n`) = 68.
 // So let's start with a buffer bigger than this.
-const initialBufSize = 128
+const initialBufSize = 256
 
 var buffersPool = sync.Pool{New: func() interface{} { return bytes.NewBuffer(make([]byte, 0, initialBufSize)) }}
 

daemon/logger/local/local.go

@@ -3,6 +3,7 @@ package local // import "github.com/docker/docker/daemon/logger/local"
 import (
 	"encoding/binary"
 	"io"
+	"math/bits"
 	"strconv"
 	"sync"
 	"time"
@@ -110,7 +111,11 @@ func marshal(m *logger.Message, buffer *[]byte) error {
 
 	buf := *buffer
 	if writeLen > cap(buf) {
-		buf = make([]byte, writeLen)
+		// If we already need to reallocate the buffer, make it larger to be more reusable.
+		// Round to the next power of two.
+		capacity := 1 << (bits.Len(uint(writeLen)) + 1)
+
+		buf = make([]byte, writeLen, capacity)
 	} else {
 		buf = buf[:writeLen]
 	}