diff --git a/weed/filesys/wfs.go b/weed/filesys/wfs.go
index c6d9080a1..f0ac6d80d 100644
--- a/weed/filesys/wfs.go
+++ b/weed/filesys/wfs.go
@@ -77,7 +77,7 @@ type WFS struct {
 	signature  int32
 
 	// throttle writers
-	concurrentWriters *util.LimitedConcurrentExecutor
+	concurrentWriters *util.LimitedOutOfOrderProcessor
 	Server            *fs.Server
 }
 type statsCache struct {
@@ -135,7 +135,7 @@ func NewSeaweedFileSystem(option *Option) *WFS {
 	wfs.fsNodeCache = newFsCache(wfs.root)
 
 	if wfs.option.ConcurrentWriters > 0 {
-		wfs.concurrentWriters = util.NewLimitedConcurrentExecutor(wfs.option.ConcurrentWriters)
+		wfs.concurrentWriters = util.NewLimitedOutOfOrderProcessor(int32(wfs.option.ConcurrentWriters))
 	}
 
 	return wfs
diff --git a/weed/operation/upload_processor.go b/weed/operation/upload_processor.go
deleted file mode 100644
index 903ae72ce..000000000
--- a/weed/operation/upload_processor.go
+++ /dev/null
@@ -1,61 +0,0 @@
-package operation
-
-import (
-	"reflect"
-	"runtime"
-	"sync"
-	"sync/atomic"
-)
-
-type OperationRequest func()
-
-var (
-	requestSlots          = uint32(32)
-	requests              = make([]chan OperationRequest, requestSlots) // increase slots to increase fairness
-	ConcurrentUploadLimit = int32(runtime.NumCPU())                     // directly related to memory usage
-	concurrentLimitCond   = sync.NewCond(new(sync.Mutex))
-	concurrentUpload      int32
-)
-
-func init() {
-
-	for i := 0; i < int(requestSlots); i++ {
-		requests[i] = make(chan OperationRequest)
-	}
-
-	cases := make([]reflect.SelectCase, requestSlots)
-	for i, ch := range requests {
-		cases[i] = reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(ch)}
-	}
-
-	go func() {
-		for {
-			_, value, ok := reflect.Select(cases)
-			if !ok {
-				continue
-			}
-
-			request := value.Interface().(OperationRequest)
-
-			concurrentLimitCond.L.Lock()
-			for atomic.LoadInt32(&concurrentUpload) > ConcurrentUploadLimit {
-				concurrentLimitCond.Wait()
-			}
-			atomic.AddInt32(&concurrentUpload, 1)
-			concurrentLimitCond.L.Unlock()
-
-			go func() {
-				defer atomic.AddInt32(&concurrentUpload, -1)
-				defer concurrentLimitCond.Signal()
-				request()
-			}()
-
-		}
-	}()
-
-}
-
-func AsyncOutOfOrderProcess(slotKey uint32, request OperationRequest) {
-	index := slotKey % requestSlots
-	requests[index] <- request
-}
diff --git a/weed/server/filer_server_handlers_write_upload.go b/weed/server/filer_server_handlers_write_upload.go
index 21af6a109..25275cf05 100644
--- a/weed/server/filer_server_handlers_write_upload.go
+++ b/weed/server/filer_server_handlers_write_upload.go
@@ -5,8 +5,8 @@ import (
 	"hash"
 	"io"
 	"io/ioutil"
-	"math/rand"
 	"net/http"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -20,6 +20,10 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
+var (
+	limitedUploadProcessor = util.NewLimitedOutOfOrderProcessor(int32(runtime.NumCPU()))
+)
+
 func (fs *FilerServer) uploadReaderToChunks(w http.ResponseWriter, r *http.Request, reader io.Reader, chunkSize int32, fileName, contentType string, contentLength int64, so *operation.StorageOption) (fileChunks []*filer_pb.FileChunk, md5Hash hash.Hash, dataSize int64, err error, smallContent []byte) {
 
 	md5Hash = md5.New()
@@ -58,7 +62,7 @@ func (fs *FilerServer) uploadReaderToChunks(w http.ResponseWriter, r *http.Reque
 	for readErr == nil {
 
 		wg.Add(1)
-		operation.AsyncOutOfOrderProcess(rand.Uint32(), func() {
+		limitedUploadProcessor.Execute(func() {
 			defer wg.Done()
 
 			var localOffset int64
diff --git a/weed/util/limiter.go b/weed/util/limiter.go
index 91499632c..2e5168d3d 100644
--- a/weed/util/limiter.go
+++ b/weed/util/limiter.go
@@ -1,40 +1,70 @@
 package util
 
-// initial version comes from https://github.com/korovkin/limiter/blob/master/limiter.go
+import (
+	"math/rand"
+	"reflect"
+	"sync"
+	"sync/atomic"
+)
 
-// LimitedConcurrentExecutor object
-type LimitedConcurrentExecutor struct {
-	limit     int
-	tokenChan chan int
+type OperationRequest func()
+
+type LimitedOutOfOrderProcessor struct {
+	processorSlots     uint32
+	processors         []chan OperationRequest
+	processorLimit     int32
+	processorLimitCond *sync.Cond
+	currentProcessor   int32
 }
 
-func NewLimitedConcurrentExecutor(limit int) *LimitedConcurrentExecutor {
+func NewLimitedOutOfOrderProcessor(limit int32) (c *LimitedOutOfOrderProcessor) {
 
-	// allocate a limiter instance
-	c := &LimitedConcurrentExecutor{
-		limit:     limit,
-		tokenChan: make(chan int, limit),
+	processorSlots := uint32(32)
+	c = &LimitedOutOfOrderProcessor{
+		processorSlots:     processorSlots,
+		processors:         make([]chan OperationRequest, processorSlots),
+		processorLimit:     limit,
+		processorLimitCond: sync.NewCond(new(sync.Mutex)),
 	}
 
-	// allocate the tokenChan:
-	for i := 0; i < c.limit; i++ {
-		c.tokenChan <- i
+	for i := 0; i < int(processorSlots); i++ {
+		c.processors[i] = make(chan OperationRequest)
 	}
 
-	return c
-}
+	cases := make([]reflect.SelectCase, processorSlots)
+	for i, ch := range c.processors {
+		cases[i] = reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(ch)}
+	}
 
-// Execute adds a function to the execution queue.
-// if num of go routines allocated by this instance is < limit
-// launch a new go routine to execute job
-// else wait until a go routine becomes available
-func (c *LimitedConcurrentExecutor) Execute(job func()) {
-	token := <-c.tokenChan
 	go func() {
-		defer func() {
-			c.tokenChan <- token
-		}()
-		// run the job
-		job()
+		for {
+			_, value, ok := reflect.Select(cases)
+			if !ok {
+				continue
+			}
+
+			request := value.Interface().(OperationRequest)
+
+			c.processorLimitCond.L.Lock()
+			for atomic.LoadInt32(&c.currentProcessor) > c.processorLimit {
+				c.processorLimitCond.Wait()
+			}
+			atomic.AddInt32(&c.currentProcessor, 1)
+			c.processorLimitCond.L.Unlock()
+
+			go func() {
+				defer atomic.AddInt32(&c.currentProcessor, -1)
+				defer c.processorLimitCond.Signal()
+				request()
+			}()
+
+		}
 	}()
+
+	return c
+}
+
+func (c *LimitedOutOfOrderProcessor) Execute(request OperationRequest) {
+	index := rand.Uint32() % c.processorSlots
+	c.processors[index] <- request
 }