perf(orch): pool NBD dispatch buffer (#2379)

Use sync.Pool for the 4 MiB dispatch buffer allocated per Handle call.
Each NBD connection allocates this buffer for reading request packets;
pooling it across connection lifecycles avoids repeated large
allocations.

Author: ValentaTomas

packages/orchestrator/pkg/sandbox/nbd/dispatch.go

@@ -34,6 +34,14 @@ var (
 
 var ErrShuttingDown = errors.New("shutting down. Cannot serve any new requests")
 
+var dispatchBufPool = sync.Pool{
+	New: func() any {
+		b := make([]byte, dispatchBufferSize)
+
+		return &b
+	},
+}
+
 type Provider interface {
 	storage.SeekableReader
 	io.WriterAt
@@ -141,7 +149,9 @@ func (d *Dispatch) writeResponse(respError uint32, respHandle uint64, chunk []by
  *
  */
 func (d *Dispatch) Handle(ctx context.Context) error {
-	buffer := make([]byte, dispatchBufferSize)
+	poolBuf := dispatchBufPool.Get().(*[]byte)
+	defer dispatchBufPool.Put(poolBuf)
+	buffer := *poolBuf
 	wp := 0
 
 	request := Request{}