After copying the input buffer, reuse it.

fuse/mountstate.go

@@ -145,25 +145,11 @@ func (me *MountState) BufferPoolStats() string {
 
 func (me *MountState) newRequest() *request {
 	r := &request{
-		status:             OK,
 		pool:               me.buffers,
-		bufferPoolInputBuf: me.buffers.AllocBuffer(uint32(me.opts.MaxWrite + 4096)),
 	}
-	r.inputBuf = r.bufferPoolInputBuf
 	return r
 }
 
-func (me *MountState) readRequest(req *request) Status {
-	n, err := me.mountFile.Read(req.inputBuf)
-	// If we start timing before the read, we may take into
-	// account waiting for input into the timing.
-	if me.latencies != nil {
-		req.startNs = time.Now().UnixNano()
-	}
-	req.inputBuf = req.inputBuf[0:n]
-	return ToStatus(err)
-}
-
 func (me *MountState) recordStats(req *request) {
 	if me.latencies != nil {
 		endNs := time.Now().UnixNano()
@@ -189,10 +175,16 @@ func (me *MountState) Loop() {
 }
 
 func (me *MountState) loop() {
+	var dest []byte
 	for {
-		req := me.newRequest()
-		errNo := me.readRequest(req)
-		if !errNo.Ok() {
+		if dest == nil {
+			dest = me.buffers.AllocBuffer(uint32(me.opts.MaxWrite + 4096))
+		}
+		
+		n, err := me.mountFile.Read(dest)
+		if err != nil {
+			errNo := ToStatus(err)
+		
 			// Retry.
 			if errNo == ENOENT {
 				continue
@@ -206,6 +198,14 @@ func (me *MountState) loop() {
 			log.Printf("Failed to read from fuse conn: %v", errNo)
 			break
 		}
+		
+		req := me.newRequest()
+		if me.latencies != nil {
+			req.startNs = time.Now().UnixNano()
+		}
+		if req.setInput(dest[:n]) {
+			dest = nil
+		}
 
 		// When closely analyzing timings, the context switch
 		// generates some delay.  While unfortunate, the

fuse/request.go

@@ -15,18 +15,16 @@ func (req *request) Discard() {
 	req.pool.FreeBuffer(req.bufferPoolInputBuf)
 }
 
-// The largest input without data is 128 (setattr). This also fits small
-// requests with short filenames.
-const SMALL_BUF_THRESHOLD = 128
-
 type request struct {
 	// the input, if obtained through bufferpool
 	bufferPoolInputBuf []byte
 	pool               BufferPool
 
-	// If we have a small input, we quickly copy it to here,
-	// and give back the large buffer to buffer pool.
-	smallInputBuf [SMALL_BUF_THRESHOLD]byte
+	// If we have a small input, we quickly copy it to here, and
+	// give back the large buffer to buffer pool.  The largest
+	// input without data is 128 (setattr). 128 also fits small
+	// requests with short filenames.
+	smallInputBuf [128]byte
 	
 	inputBuf []byte
 
@@ -103,6 +101,18 @@ func (me *request) OutputDebug() string {
 		operationName(me.inHeader.Opcode), me.status, dataStr, flatStr)
 }
 
+// setInput returns true if it takes ownership of the argument, false if not.
+func (me *request) setInput(input []byte) bool {
+	if len(input) < len(me.smallInputBuf) {
+		copy(me.smallInputBuf[:], input)
+		me.inputBuf = me.smallInputBuf[:len(input)]
+		return false
+	} 
+	me.inputBuf = input
+	me.bufferPoolInputBuf = input
+	
+	return true
+}
 
 func (me *request) parse() {
 	inHSize := int(unsafe.Sizeof(raw.InHeader{}))
@@ -111,16 +121,6 @@ func (me *request) parse() {
 		return
 	}
 
-	// We return the input buffer early if possible. Only write
-	// requests require a large input buffer, so if we hang onto
-	// the large buffer, we create unnecessary memory pressure.
-	if len(me.inputBuf) < SMALL_BUF_THRESHOLD {
-		copy(me.smallInputBuf[:], me.inputBuf)
-		me.inputBuf = me.smallInputBuf[:len(me.inputBuf)]
-		me.pool.FreeBuffer(me.bufferPoolInputBuf)
-		me.bufferPoolInputBuf = nil
-	}
-	
 	me.inHeader = (*raw.InHeader)(unsafe.Pointer(&me.inputBuf[0]))
 	me.arg = me.inputBuf[inHSize:]