mount: shortcut when there is only one chunk

weed/filesys/dirty_page_interval.go

@@ -3,6 +3,8 @@ package filesys
 import (
 	"bytes"
 	"io"
+
+	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
 type IntervalNode struct {
@@ -200,10 +202,13 @@ func (c *ContinuousIntervals) ReadDataAt(data []byte, startOffset int64) (maxSto
 func (l *IntervalLinkedList) ToReader() io.Reader {
 	var readers []io.Reader
 	t := l.Head
-	readers = append(readers, bytes.NewReader(t.Data))
+	readers = append(readers, util.NewBytesReader(t.Data))
 	for t.Next != nil {
 		t = t.Next
 		readers = append(readers, bytes.NewReader(t.Data))
 	}
+	if len(readers) == 1 {
+		return readers[0]
+	}
 	return io.MultiReader(readers...)
 }