bytes: use padding as bootstarp

Signed-off-by: Maxim Eryomenko <[email protected]>

Author: moeryomenko

src/bytes/buffer.go

@@ -23,8 +23,9 @@ type Buffer struct {
 	off      int    // read at &buf[off], write at &buf[len(buf)]
 	lastRead readOp // last read operation, so that Unread* can work correctly.
 
-	// This is padding for Buffer to cache lines to avoid false sharing.
-	_ [cpu.BufferPaddingSize]byte
+	// memory to hold first slice; helps small buffers (Printf) avoid allocation.
+	// Also it's padding for Buffer to cache lines to avoid false sharing.
+	bootstrap [cpu.BufferPaddingSize]byte
 }
 
 // The readOp constants describe the last action performed on
@@ -128,9 +129,15 @@ func (b *Buffer) grow(n int) int {
 	if i, ok := b.tryGrowByReslice(n); ok {
 		return i
 	}
-	if b.buf == nil && n <= smallBufferSize {
-		b.buf = make([]byte, n, smallBufferSize)
-		return 0
+	if b.buf == nil {
+		switch {
+		case n <= cpu.BufferPaddingSize:
+			buf = b.bootstrap[0:]
+			return 0
+		case n <= smallBufferSize:
+			b.buf = make([]byte, n, smallBufferSize)
+			return 0
+		}
 	}
 	c := cap(b.buf)
 	if n <= c/2-m {