Make async buffering start slowly to improve seek performance

fs/buffer.go

@@ -7,7 +7,10 @@ import (
 	"github.com/pkg/errors"
 )
 
-const asyncBufferSize = 128 * 1024
+const (
+	asyncBufferSize  = 1024 * 1024
+	softStartInitial = 4 * 1024
+)
 
 var asyncBufferPool = sync.Pool{
 	New: func() interface{} { return newBuffer() },
@@ -26,6 +29,7 @@ type asyncReader struct {
 	err     error         // If an error has occurred it is here
 	cur     *buffer       // Current buffer being served
 	exited  chan struct{} // Channel is closed been the async reader shuts down
+	size    int           // size of buffer to use
 }
 
 // newAsyncReader returns a reader that will asynchronously read from
@@ -54,6 +58,7 @@ func (a *asyncReader) init(rd io.ReadCloser, buffers int) {
 	a.exited = make(chan struct{}, 0)
 	a.buffers = buffers
 	a.cur = nil
+	a.size = softStartInitial
 
 	// Create tokens
 	for i := 0; i < buffers; i++ {
@@ -69,6 +74,10 @@ func (a *asyncReader) init(rd io.ReadCloser, buffers int) {
 			select {
 			case <-a.token:
 				b := a.getBuffer()
+				if a.size < asyncBufferSize {
+					b.buf = b.buf[:a.size]
+					a.size <<= 1
+				}
 				err := b.read(a.in)
 				a.ready <- b
 				if err != nil {
@@ -89,7 +98,8 @@ func (a *asyncReader) putBuffer(b *buffer) {
 
 // get a buffer from the pool
 func (a *asyncReader) getBuffer() *buffer {
-	return asyncBufferPool.Get().(*buffer)
+	b := asyncBufferPool.Get().(*buffer)
+	return b
 }
 
 // Read will return the next available data.