diff --git a/weed/filesys/page_writer/mem_chunk.go b/weed/filesys/page_writer/mem_chunk.go
new file mode 100644
index 000000000..422240bd8
--- /dev/null
+++ b/weed/filesys/page_writer/mem_chunk.go
@@ -0,0 +1,64 @@
+package page_writer
+
+import (
+	"github.com/chrislusf/seaweedfs/weed/util"
+	"github.com/chrislusf/seaweedfs/weed/util/mem"
+)
+
+var (
+	_ = PageChunk(&MemChunk{})
+)
+
+type MemChunk struct {
+	buf             []byte
+	usage           *ChunkWrittenIntervalList
+	chunkSize       int64
+	logicChunkIndex LogicChunkIndex
+}
+
+func NewMemChunk(logicChunkIndex LogicChunkIndex, chunkSize int64) *MemChunk {
+	return &MemChunk{
+		logicChunkIndex: logicChunkIndex,
+		chunkSize:       chunkSize,
+		buf:             mem.Allocate(int(chunkSize)),
+		usage:           newChunkWrittenIntervalList(),
+	}
+}
+
+func (mc *MemChunk) FreeResource() {
+	mem.Free(mc.buf)
+}
+
+func (mc *MemChunk) WriteDataAt(src []byte, offset int64) (n int) {
+	n = copy(mc.buf[offset:], src)
+	mc.usage.MarkWritten(offset, offset+int64(n))
+	return
+}
+
+func (mc *MemChunk) ReadDataAt(p []byte, off int64) (maxStop int64) {
+	memChunkBaseOffset := int64(mc.logicChunkIndex) * mc.chunkSize
+	for t := mc.usage.head.next; t != mc.usage.tail; t = t.next {
+		logicStart := max(off, int64(mc.logicChunkIndex)*mc.chunkSize+t.StartOffset)
+		logicStop := min(off+int64(len(p)), memChunkBaseOffset+t.stopOffset)
+		if logicStart < logicStop {
+			copy(p[logicStart-off:logicStop-off], mc.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
+			maxStop = max(maxStop, logicStop)
+		}
+	}
+	return
+}
+
+func (mc *MemChunk) IsComplete() bool {
+	return mc.usage.IsComplete(mc.chunkSize)
+}
+
+func (mc *MemChunk) SaveContent(saveFn SaveToStorageFunc) {
+	if saveFn == nil {
+		return
+	}
+	for t := mc.usage.head.next; t != mc.usage.tail; t = t.next {
+		reader := util.NewBytesReader(mc.buf[t.StartOffset:t.stopOffset])
+		saveFn(reader, int64(mc.logicChunkIndex)*mc.chunkSize+t.StartOffset, t.Size(), func() {
+		})
+	}
+}
diff --git a/weed/filesys/page_writer/page_chunk.go b/weed/filesys/page_writer/page_chunk.go
index 1c892ddb6..d1f3a5745 100644
--- a/weed/filesys/page_writer/page_chunk.go
+++ b/weed/filesys/page_writer/page_chunk.go
@@ -1,8 +1,6 @@
 package page_writer
 
 import (
-	"github.com/chrislusf/seaweedfs/weed/util"
-	"github.com/chrislusf/seaweedfs/weed/util/mem"
 	"io"
 )
 
@@ -15,61 +13,3 @@ type PageChunk interface {
 	IsComplete() bool
 	SaveContent(saveFn SaveToStorageFunc)
 }
-
-var (
-	_ = PageChunk(&MemChunk{})
-)
-
-type MemChunk struct {
-	buf             []byte
-	usage           *ChunkWrittenIntervalList
-	chunkSize       int64
-	logicChunkIndex LogicChunkIndex
-}
-
-func NewMemChunk(logicChunkIndex LogicChunkIndex, chunkSize int64) *MemChunk {
-	return &MemChunk{
-		logicChunkIndex: logicChunkIndex,
-		chunkSize:       chunkSize,
-		buf:             mem.Allocate(int(chunkSize)),
-		usage:           newChunkWrittenIntervalList(),
-	}
-}
-
-func (mc *MemChunk) FreeResource() {
-	mem.Free(mc.buf)
-}
-
-func (mc *MemChunk) WriteDataAt(src []byte, offset int64) (n int) {
-	n = copy(mc.buf[offset:], src)
-	mc.usage.MarkWritten(offset, offset+int64(n))
-	return
-}
-
-func (mc *MemChunk) ReadDataAt(p []byte, off int64) (maxStop int64) {
-	memChunkBaseOffset := int64(mc.logicChunkIndex) * mc.chunkSize
-	for t := mc.usage.head.next; t != mc.usage.tail; t = t.next {
-		logicStart := max(off, int64(mc.logicChunkIndex)*mc.chunkSize+t.StartOffset)
-		logicStop := min(off+int64(len(p)), memChunkBaseOffset+t.stopOffset)
-		if logicStart < logicStop {
-			copy(p[logicStart-off:logicStop-off], mc.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
-			maxStop = max(maxStop, logicStop)
-		}
-	}
-	return
-}
-
-func (mc *MemChunk) IsComplete() bool {
-	return mc.usage.IsComplete(mc.chunkSize)
-}
-
-func (mc *MemChunk) SaveContent(saveFn SaveToStorageFunc) {
-	if saveFn == nil {
-		return
-	}
-	for t := mc.usage.head.next; t != mc.usage.tail; t = t.next {
-		reader := util.NewBytesReader(mc.buf[t.StartOffset:t.stopOffset])
-		saveFn(reader, int64(mc.logicChunkIndex)*mc.chunkSize+t.StartOffset, t.Size(), func() {
-		})
-	}
-}