diff --git a/weed/filesys/dirty_page.go b/weed/filesys/dirty_page.go
index 3418dc1c9..f1532a6a0 100644
--- a/weed/filesys/dirty_page.go
+++ b/weed/filesys/dirty_page.go
@@ -4,8 +4,8 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"io"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
@@ -15,28 +15,19 @@ import (
 )
 
 type ContinuousDirtyPages struct {
-	hasData bool
-	Offset  int64
-	Size    int64
-	Data    []byte
-	f       *File
-	lock    sync.Mutex
+	intervals *ContinuousIntervals
+	f         *File
+	lock      sync.Mutex
 }
 
 func newDirtyPages(file *File) *ContinuousDirtyPages {
 	return &ContinuousDirtyPages{
-		Data: nil,
-		f:    file,
+		intervals: &ContinuousIntervals{},
+		f:         file,
 	}
 }
 
 func (pages *ContinuousDirtyPages) releaseResource() {
-	if pages.Data != nil {
-		pages.f.wfs.bufPool.Put(pages.Data)
-		pages.Data = nil
-		atomic.AddInt32(&counter, -1)
-		glog.V(3).Infof("%s/%s releasing resource %d", pages.f.dir.Path, pages.f.Name, counter)
-	}
 }
 
 var counter = int32(0)
@@ -46,84 +37,49 @@ func (pages *ContinuousDirtyPages) AddPage(ctx context.Context, offset int64, da
 	pages.lock.Lock()
 	defer pages.lock.Unlock()
 
-	var chunk *filer_pb.FileChunk
+	glog.V(3).Infof("%s AddPage [%d,%d)", pages.f.fullpath(), offset, offset+int64(len(data)))
 
 	if len(data) > int(pages.f.wfs.option.ChunkSizeLimit) {
 		// this is more than what buffer can hold.
 		return pages.flushAndSave(ctx, offset, data)
 	}
 
-	if pages.Data == nil {
-		pages.Data = pages.f.wfs.bufPool.Get().([]byte)
-		atomic.AddInt32(&counter, 1)
-		glog.V(3).Infof("%s/%s acquire resource %d", pages.f.dir.Path, pages.f.Name, counter)
-	}
-
-	if offset < pages.Offset || offset >= pages.Offset+int64(len(pages.Data)) ||
-		pages.Offset+int64(len(pages.Data)) < offset+int64(len(data)) {
-		// if the data is out of range,
-		// or buffer is full if adding new data,
-		// flush current buffer and add new data
-
-		glog.V(4).Infof("offset=%d, size=%d, existing pages offset=%d, pages size=%d, data=%d", offset, len(data), pages.Offset, pages.Size, len(pages.Data))
-
-		if chunk, err = pages.saveExistingPagesToStorage(ctx); err == nil {
-			if chunk != nil {
-				glog.V(4).Infof("%s/%s add save [%d,%d)", pages.f.dir.Path, pages.f.Name, chunk.Offset, chunk.Offset+int64(chunk.Size))
-				chunks = append(chunks, chunk)
-			}
-		} else {
-			glog.V(0).Infof("%s/%s add save [%d,%d): %v", pages.f.dir.Path, pages.f.Name, chunk.Offset, chunk.Offset+int64(chunk.Size), err)
-			return
-		}
-		pages.Offset = offset
-		glog.V(4).Infof("copy data0: offset=%d, size=%d, existing pages offset=%d, pages size=%d, data=%d", offset, len(data), pages.Offset, pages.Size, len(pages.Data))
-		copy(pages.Data, data)
-		pages.Size = int64(len(data))
+	hasOverlap := pages.intervals.AddInterval(data, offset)
+	if hasOverlap {
+		chunks, err = pages.saveExistingPagesToStorage(ctx)
+		pages.intervals.AddInterval(data, offset)
 		return
 	}
 
-	if offset != pages.Offset+pages.Size {
-		// when this happens, debug shows the data overlapping with existing data is empty
-		// the data is not just append
-		if offset == pages.Offset && int(pages.Size) < len(data) {
-			glog.V(4).Infof("copy data1: offset=%d, size=%d, existing pages offset=%d, pages size=%d, data=%d", offset, len(data), pages.Offset, pages.Size, len(pages.Data))
-			copy(pages.Data[pages.Size:], data[pages.Size:])
-		} else {
-			if pages.Size != 0 {
-				glog.V(1).Infof("%s/%s add page: pages [%d, %d) write [%d, %d)", pages.f.dir.Path, pages.f.Name, pages.Offset, pages.Offset+pages.Size, offset, offset+int64(len(data)))
-			}
-			return pages.flushAndSave(ctx, offset, data)
+	var chunk *filer_pb.FileChunk
+	var hasSavedData bool
+
+	if pages.intervals.TotalSize() > pages.f.wfs.option.ChunkSizeLimit {
+		chunk, hasSavedData, err = pages.saveExistingLargestPageToStorage(ctx)
+		if hasSavedData {
+			chunks = append(chunks, chunk)
 		}
-	} else {
-		glog.V(4).Infof("copy data2: offset=%d, size=%d, existing pages offset=%d, pages size=%d, data=%d", offset, len(data), pages.Offset, pages.Size, len(pages.Data))
-		copy(pages.Data[offset-pages.Offset:], data)
 	}
 
-	pages.Size = max(pages.Size, offset+int64(len(data))-pages.Offset)
-
 	return
 }
 
 func (pages *ContinuousDirtyPages) flushAndSave(ctx context.Context, offset int64, data []byte) (chunks []*filer_pb.FileChunk, err error) {
 
 	var chunk *filer_pb.FileChunk
+	var newChunks []*filer_pb.FileChunk
 
 	// flush existing
-	if chunk, err = pages.saveExistingPagesToStorage(ctx); err == nil {
-		if chunk != nil {
-			glog.V(4).Infof("%s/%s flush existing [%d,%d) to %s", pages.f.dir.Path, pages.f.Name, chunk.Offset, chunk.Offset+int64(chunk.Size), chunk.FileId)
-			chunks = append(chunks, chunk)
+	if newChunks, err = pages.saveExistingPagesToStorage(ctx); err == nil {
+		if newChunks != nil {
+			chunks = append(chunks, newChunks...)
 		}
 	} else {
-		glog.V(0).Infof("%s/%s failed to flush1 [%d,%d): %v", pages.f.dir.Path, pages.f.Name, chunk.Offset, chunk.Offset+int64(chunk.Size), err)
 		return
 	}
-	pages.Size = 0
-	pages.Offset = 0
 
 	// flush the new page
-	if chunk, err = pages.saveToStorage(ctx, data, offset); err == nil {
+	if chunk, err = pages.saveToStorage(ctx, bytes.NewReader(data), offset, int64(len(data))); err == nil {
 		if chunk != nil {
 			glog.V(4).Infof("%s/%s flush big request [%d,%d) to %s", pages.f.dir.Path, pages.f.Name, chunk.Offset, chunk.Offset+int64(chunk.Size), chunk.FileId)
 			chunks = append(chunks, chunk)
@@ -136,37 +92,55 @@ func (pages *ContinuousDirtyPages) flushAndSave(ctx context.Context, offset int6
 	return
 }
 
-func (pages *ContinuousDirtyPages) FlushToStorage(ctx context.Context) (chunk *filer_pb.FileChunk, err error) {
+func (pages *ContinuousDirtyPages) FlushToStorage(ctx context.Context) (chunks []*filer_pb.FileChunk, err error) {
 
 	pages.lock.Lock()
 	defer pages.lock.Unlock()
 
-	if pages.Size == 0 {
-		return nil, nil
-	}
+	return pages.saveExistingPagesToStorage(ctx)
+}
 
-	if chunk, err = pages.saveExistingPagesToStorage(ctx); err == nil {
-		pages.Size = 0
-		pages.Offset = 0
-		if chunk != nil {
-			glog.V(4).Infof("%s/%s flush [%d,%d)", pages.f.dir.Path, pages.f.Name, chunk.Offset, chunk.Offset+int64(chunk.Size))
+func (pages *ContinuousDirtyPages) saveExistingPagesToStorage(ctx context.Context) (chunks []*filer_pb.FileChunk, err error) {
+
+	var hasSavedData bool
+	var chunk *filer_pb.FileChunk
+
+	for {
+
+		chunk, hasSavedData, err = pages.saveExistingLargestPageToStorage(ctx)
+		if !hasSavedData {
+			return chunks, err
+		}
+
+		if err == nil {
+			chunks = append(chunks, chunk)
+		} else {
+			return
 		}
 	}
-	return
+
 }
 
-func (pages *ContinuousDirtyPages) saveExistingPagesToStorage(ctx context.Context) (*filer_pb.FileChunk, error) {
+func (pages *ContinuousDirtyPages) saveExistingLargestPageToStorage(ctx context.Context) (chunk *filer_pb.FileChunk, hasSavedData bool, err error) {
 
-	if pages.Size == 0 {
-		return nil, nil
+	maxList := pages.intervals.RemoveLargestIntervalLinkedList()
+	if maxList == nil {
+		return nil, false, nil
 	}
 
-	glog.V(0).Infof("%s/%s saveExistingPagesToStorage [%d,%d): Data len=%d", pages.f.dir.Path, pages.f.Name, pages.Offset, pages.Size, len(pages.Data))
+	chunk, err = pages.saveToStorage(ctx, maxList.ToReader(), maxList.Offset(), maxList.Size())
+	if err == nil {
+		hasSavedData = true
+		glog.V(3).Infof("%s saveToStorage [%d,%d) %s", pages.f.fullpath(), maxList.Offset(), maxList.Offset()+maxList.Size(), chunk.FileId)
+	} else {
+		glog.V(0).Infof("%s saveToStorage [%d,%d): %v", pages.f.fullpath(), maxList.Offset(), maxList.Offset()+maxList.Size(), err)
+		return
+	}
 
-	return pages.saveToStorage(ctx, pages.Data[:pages.Size], pages.Offset)
+	return
 }
 
-func (pages *ContinuousDirtyPages) saveToStorage(ctx context.Context, buf []byte, offset int64) (*filer_pb.FileChunk, error) {
+func (pages *ContinuousDirtyPages) saveToStorage(ctx context.Context, reader io.Reader, offset int64, size int64) (*filer_pb.FileChunk, error) {
 
 	var fileId, host string
 	var auth security.EncodedJwt
@@ -195,8 +169,7 @@ func (pages *ContinuousDirtyPages) saveToStorage(ctx context.Context, buf []byte
 	}
 
 	fileUrl := fmt.Sprintf("http://%s/%s", host, fileId)
-	bufReader := bytes.NewReader(buf)
-	uploadResult, err := operation.Upload(fileUrl, pages.f.Name, bufReader, false, "", nil, auth)
+	uploadResult, err := operation.Upload(fileUrl, pages.f.Name, reader, false, "", nil, auth)
 	if err != nil {
 		glog.V(0).Infof("upload data %v to %s: %v", pages.f.Name, fileUrl, err)
 		return nil, fmt.Errorf("upload data: %v", err)
@@ -209,7 +182,7 @@ func (pages *ContinuousDirtyPages) saveToStorage(ctx context.Context, buf []byte
 	return &filer_pb.FileChunk{
 		FileId: fileId,
 		Offset: offset,
-		Size:   uint64(len(buf)),
+		Size:   uint64(size),
 		Mtime:  time.Now().UnixNano(),
 		ETag:   uploadResult.ETag,
 	}, nil
@@ -229,23 +202,11 @@ func min(x, y int64) int64 {
 	return y
 }
 
-func (pages *ContinuousDirtyPages) ReadDirtyData(ctx context.Context, data []byte, startOffset int64) (offset int64, size int, err error) {
-	bufSize := int64(len(data))
+func (pages *ContinuousDirtyPages) ReadDirtyData(ctx context.Context, data []byte, startOffset int64) (offset int64, size int) {
 
 	pages.lock.Lock()
 	defer pages.lock.Unlock()
 
-	if startOffset+bufSize < pages.Offset {
-		return
-	}
-	if startOffset >= pages.Offset+pages.Size {
-		return
-	}
-
-	offset = max(pages.Offset, startOffset)
-	stopOffset := min(pages.Offset+pages.Size, startOffset+bufSize)
-	size = int(stopOffset - offset)
-	copy(data[offset-startOffset:], pages.Data[offset-pages.Offset:stopOffset-pages.Offset])
+	return pages.intervals.ReadData(data, startOffset)
 
-	return
 }
diff --git a/weed/filesys/dirty_page_interval.go b/weed/filesys/dirty_page_interval.go
new file mode 100644
index 000000000..5c55268c7
--- /dev/null
+++ b/weed/filesys/dirty_page_interval.go
@@ -0,0 +1,190 @@
+package filesys
+
+import (
+	"bytes"
+	"io"
+	"math"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+type IntervalNode struct {
+	Data   []byte
+	Offset int64
+	Size   int64
+	Next   *IntervalNode
+}
+
+type IntervalLinkedList struct {
+	Head *IntervalNode
+	Tail *IntervalNode
+}
+
+type ContinuousIntervals struct {
+	lists []*IntervalLinkedList
+}
+
+func (list *IntervalLinkedList) Offset() int64 {
+	return list.Head.Offset
+}
+func (list *IntervalLinkedList) Size() int64 {
+	return list.Tail.Offset + list.Tail.Size - list.Head.Offset
+}
+func (list *IntervalLinkedList) addNodeToTail(node *IntervalNode) {
+	// glog.V(0).Infof("add to tail [%d,%d) + [%d,%d) => [%d,%d)", list.Head.Offset, list.Tail.Offset+list.Tail.Size, node.Offset, node.Offset+node.Size, list.Head.Offset, node.Offset+node.Size)
+	list.Tail.Next = node
+	list.Tail = node
+}
+func (list *IntervalLinkedList) addNodeToHead(node *IntervalNode) {
+	// glog.V(0).Infof("add to head [%d,%d) + [%d,%d) => [%d,%d)", node.Offset, node.Offset+node.Size, list.Head.Offset, list.Tail.Offset+list.Tail.Size, node.Offset, list.Tail.Offset+list.Tail.Size)
+	node.Next = list.Head
+	list.Head = node
+}
+
+func (list *IntervalLinkedList) ReadData(buf []byte, start, stop int64) {
+	t := list.Head
+	for {
+
+		nodeStart, nodeStop := max(start, t.Offset), min(stop, t.Offset+t.Size)
+		if nodeStart < nodeStop {
+			glog.V(0).Infof("copying start=%d stop=%d t=[%d,%d) t.data=%d => bufSize=%d nodeStart=%d, nodeStop=%d",
+				start, stop, t.Offset, t.Offset+t.Size, len(t.Data),
+				len(buf), nodeStart, nodeStop)
+			copy(buf[nodeStart-start:], t.Data[nodeStart-t.Offset:nodeStop-t.Offset])
+		}
+
+		if t.Next == nil {
+			break
+		}
+		t = t.Next
+	}
+}
+
+func (c *ContinuousIntervals) TotalSize() (total int64) {
+	for _, list := range c.lists {
+		total += list.Size()
+	}
+	return
+}
+
+func (c *ContinuousIntervals) AddInterval(data []byte, offset int64) (hasOverlap bool) {
+	interval := &IntervalNode{Data: data, Offset: offset, Size: int64(len(data))}
+
+	var prevList, nextList *IntervalLinkedList
+
+	for _, list := range c.lists {
+		if list.Head.Offset == interval.Offset+interval.Size {
+			nextList = list
+			break
+		}
+	}
+
+	for _, list := range c.lists {
+		if list.Head.Offset+list.Size() == offset {
+			list.addNodeToTail(interval)
+			prevList = list
+			break
+		}
+		if list.Head.Offset <= offset && offset < list.Head.Offset+list.Size() {
+			if list.Tail.Offset <= offset {
+				dataStartIndex := list.Tail.Offset + list.Tail.Size - offset
+				// glog.V(4).Infof("overlap data new [0,%d) same=%v", dataStartIndex, bytes.Compare(interval.Data[0:dataStartIndex], list.Tail.Data[len(list.Tail.Data)-int(dataStartIndex):]))
+				interval.Data = interval.Data[dataStartIndex:]
+				interval.Size -= dataStartIndex
+				interval.Offset = offset + dataStartIndex
+				// glog.V(4).Infof("overlapping append as [%d,%d) dataSize=%d", interval.Offset, interval.Offset+interval.Size, len(interval.Data))
+				list.addNodeToTail(interval)
+				prevList = list
+				break
+			}
+			glog.V(4).Infof("overlapped! interval is [%d,%d) dataSize=%d", interval.Offset, interval.Offset+interval.Size, len(interval.Data))
+			hasOverlap = true
+			return
+		}
+	}
+
+	if prevList != nil && nextList != nil {
+		// glog.V(4).Infof("connecting [%d,%d) + [%d,%d) => [%d,%d)", prevList.Head.Offset, prevList.Tail.Offset+prevList.Tail.Size, nextList.Head.Offset, nextList.Tail.Offset+nextList.Tail.Size, prevList.Head.Offset, nextList.Tail.Offset+nextList.Tail.Size)
+		prevList.Tail.Next = nextList.Head
+		prevList.Tail = nextList.Tail
+		c.removeList(nextList)
+	} else if nextList != nil {
+		// add to head was not done when checking
+		nextList.addNodeToHead(interval)
+	}
+	if prevList == nil && nextList == nil {
+		c.lists = append(c.lists, &IntervalLinkedList{
+			Head: interval,
+			Tail: interval,
+		})
+	}
+
+	return
+}
+
+func (c *ContinuousIntervals) RemoveLargestIntervalLinkedList() *IntervalLinkedList {
+	var maxSize int64
+	maxIndex := -1
+	for k, list := range c.lists {
+		if maxSize <= list.Size() {
+			maxSize = list.Size()
+			maxIndex = k
+		}
+	}
+	if maxSize <= 0 {
+		return nil
+	}
+
+	t := c.lists[maxIndex]
+	c.lists = append(c.lists[0:maxIndex], c.lists[maxIndex+1:]...)
+	return t
+
+}
+
+func (c *ContinuousIntervals) removeList(target *IntervalLinkedList) {
+	index := -1
+	for k, list := range c.lists {
+		if list.Offset() == target.Offset() {
+			index = k
+		}
+	}
+	if index < 0 {
+		return
+	}
+
+	c.lists = append(c.lists[0:index], c.lists[index+1:]...)
+
+}
+
+func (c *ContinuousIntervals) ReadData(data []byte, startOffset int64) (offset int64, size int) {
+	var minOffset int64 = math.MaxInt64
+	var maxStop int64
+	for _, list := range c.lists {
+		start := max(startOffset, list.Offset())
+		stop := min(startOffset+int64(len(data)), list.Offset()+list.Size())
+		if start <= stop {
+			list.ReadData(data[start-startOffset:], start, stop)
+			minOffset = min(minOffset, start)
+			maxStop = max(maxStop, stop)
+		}
+	}
+
+	if minOffset == math.MaxInt64 {
+		return 0, 0
+	}
+
+	offset = minOffset
+	size = int(maxStop - offset)
+	return
+}
+
+func (l *IntervalLinkedList) ToReader() io.Reader {
+	var readers []io.Reader
+	t := l.Head
+	readers = append(readers, bytes.NewReader(t.Data))
+	for t.Next != nil {
+		t = t.Next
+		readers = append(readers, bytes.NewReader(t.Data))
+	}
+	return io.MultiReader(readers...)
+}
diff --git a/weed/filesys/file.go b/weed/filesys/file.go
index b1d53507b..5a823f516 100644
--- a/weed/filesys/file.go
+++ b/weed/filesys/file.go
@@ -230,12 +230,6 @@ func (file *File) maybeLoadEntry(ctx context.Context) error {
 	return nil
 }
 
-func (file *File) addChunk(chunk *filer_pb.FileChunk) {
-	if chunk != nil {
-		file.addChunks([]*filer_pb.FileChunk{chunk})
-	}
-}
-
 func (file *File) addChunks(chunks []*filer_pb.FileChunk) {
 
 	sort.Slice(chunks, func(i, j int) bool {
diff --git a/weed/filesys/filehandle.go b/weed/filesys/filehandle.go
index 981de7ea2..c3f06ae8a 100644
--- a/weed/filesys/filehandle.go
+++ b/weed/filesys/filehandle.go
@@ -55,8 +55,8 @@ func (fh *FileHandle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fus
 
 	totalRead, err := fh.readFromChunks(ctx, buff, req.Offset)
 	if err == nil {
-		dirtyOffset, dirtySize, dirtyReadErr := fh.readFromDirtyPages(ctx, buff, req.Offset)
-		if dirtyReadErr == nil && totalRead+req.Offset < dirtyOffset+int64(dirtySize) {
+		dirtyOffset, dirtySize := fh.readFromDirtyPages(ctx, buff, req.Offset)
+		if totalRead+req.Offset < dirtyOffset+int64(dirtySize) {
 			totalRead = dirtyOffset + int64(dirtySize) - req.Offset
 		}
 	}
@@ -70,7 +70,7 @@ func (fh *FileHandle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fus
 	return err
 }
 
-func (fh *FileHandle) readFromDirtyPages(ctx context.Context, buff []byte, startOffset int64) (offset int64, size int, err error) {
+func (fh *FileHandle) readFromDirtyPages(ctx context.Context, buff []byte, startOffset int64) (offset int64, size int) {
 	return fh.dirtyPages.ReadDirtyData(ctx, buff, startOffset)
 }
 
@@ -102,8 +102,6 @@ func (fh *FileHandle) Write(ctx context.Context, req *fuse.WriteRequest, resp *f
 
 	// write the request to volume servers
 
-	glog.V(4).Infof("%+v/%v write fh %d: [%d,%d)", fh.f.dir.Path, fh.f.Name, fh.handle, req.Offset, req.Offset+int64(len(req.Data)))
-
 	chunks, err := fh.dirtyPages.AddPage(ctx, req.Offset, req.Data)
 	if err != nil {
 		glog.Errorf("%+v/%v write fh %d: [%d,%d): %v", fh.f.dir.Path, fh.f.Name, fh.handle, req.Offset, req.Offset+int64(len(req.Data)), err)
@@ -152,13 +150,16 @@ func (fh *FileHandle) Flush(ctx context.Context, req *fuse.FlushRequest) error {
 	// send the data to the OS
 	glog.V(4).Infof("%s fh %d flush %v", fh.f.fullpath(), fh.handle, req)
 
-	chunk, err := fh.dirtyPages.FlushToStorage(ctx)
+	chunks, err := fh.dirtyPages.FlushToStorage(ctx)
 	if err != nil {
 		glog.Errorf("flush %s/%s: %v", fh.f.dir.Path, fh.f.Name, err)
 		return fmt.Errorf("flush %s/%s: %v", fh.f.dir.Path, fh.f.Name, err)
 	}
 
-	fh.f.addChunk(chunk)
+	fh.f.addChunks(chunks)
+	if len(chunks) > 0 {
+		fh.dirtyMetadata = true
+	}
 
 	if !fh.dirtyMetadata {
 		return nil