diff --git a/weed/filesys/page_writer/page_chunk_interval_list.go b/weed/filesys/page_writer/page_chunk_interval_list.go
new file mode 100644
index 000000000..e626b2a7f
--- /dev/null
+++ b/weed/filesys/page_writer/page_chunk_interval_list.go
@@ -0,0 +1,96 @@
+package page_writer
+
+import "math"
+
+// PageChunkWrittenInterval mark one written interval within one page chunk
+type PageChunkWrittenInterval struct {
+	startOffset int64
+	stopOffset  int64
+	prev        *PageChunkWrittenInterval
+	next        *PageChunkWrittenInterval
+}
+
+// PageChunkWrittenIntervalList mark written intervals within one page chunk
+type PageChunkWrittenIntervalList struct {
+	head *PageChunkWrittenInterval
+	tail *PageChunkWrittenInterval
+}
+
+func newPageChunkWrittenIntervalList() *PageChunkWrittenIntervalList {
+	list := &PageChunkWrittenIntervalList{
+		head: &PageChunkWrittenInterval{
+			startOffset: -1,
+			stopOffset:  -1,
+		},
+		tail: &PageChunkWrittenInterval{
+			startOffset: math.MaxInt64,
+			stopOffset:  math.MaxInt64,
+		},
+	}
+	list.head.next = list.tail
+	list.tail.prev = list.head
+	return list
+}
+
+func (list *PageChunkWrittenIntervalList) MarkWritten(startOffset, stopOffset int64) {
+	interval := &PageChunkWrittenInterval{
+		startOffset: startOffset,
+		stopOffset:  stopOffset,
+	}
+	list.addInterval(interval)
+}
+func (list *PageChunkWrittenIntervalList) addInterval(interval *PageChunkWrittenInterval) {
+
+	p := list.head
+	for ; p.next != nil && p.next.startOffset <= interval.startOffset; p = p.next {
+	}
+	q := list.tail
+	for ; q.prev != nil && q.prev.stopOffset >= interval.stopOffset; q = q.prev {
+	}
+
+	if interval.startOffset <= p.stopOffset && q.startOffset <= interval.stopOffset {
+		// merge p and q together
+		p.stopOffset = q.stopOffset
+		unlinkNodesBetween(p, q.next)
+		return
+	}
+	if interval.startOffset <= p.stopOffset {
+		// merge new interval into p
+		p.stopOffset = interval.stopOffset
+		unlinkNodesBetween(p, q)
+		return
+	}
+	if q.startOffset <= interval.stopOffset {
+		// merge new interval into q
+		q.startOffset = interval.startOffset
+		unlinkNodesBetween(p, q)
+		return
+	}
+
+	// add the new interval between p and q
+	unlinkNodesBetween(p, q)
+	p.next = interval
+	interval.prev = p
+	q.prev = interval
+	interval.next = q
+
+}
+
+// unlinkNodesBetween remove all nodes after start and before stop, exclusive
+func unlinkNodesBetween(start *PageChunkWrittenInterval, stop *PageChunkWrittenInterval) {
+	if start.next == stop {
+		return
+	}
+	start.next.prev = nil
+	start.next = stop
+	stop.prev.next = nil
+	stop.prev = start
+}
+
+func (list *PageChunkWrittenIntervalList) size() int {
+	var count int
+	for t := list.head; t != nil; t = t.next {
+		count++
+	}
+	return count - 2
+}
diff --git a/weed/filesys/page_writer/page_chunk_interval_list_test.go b/weed/filesys/page_writer/page_chunk_interval_list_test.go
new file mode 100644
index 000000000..f54b229d8
--- /dev/null
+++ b/weed/filesys/page_writer/page_chunk_interval_list_test.go
@@ -0,0 +1,49 @@
+package page_writer
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func Test_PageChunkWrittenIntervalList(t *testing.T) {
+	list := newPageChunkWrittenIntervalList()
+
+	assert.Equal(t, 0, list.size(), "empty list")
+
+	list.MarkWritten(0, 5)
+	assert.Equal(t, 1, list.size(), "one interval")
+
+	list.MarkWritten(0, 5)
+	assert.Equal(t, 1, list.size(), "duplicated interval2")
+
+	list.MarkWritten(95, 100)
+	assert.Equal(t, 2, list.size(), "two intervals")
+
+	list.MarkWritten(50, 60)
+	assert.Equal(t, 3, list.size(), "three intervals")
+
+	list.MarkWritten(50, 55)
+	assert.Equal(t, 3, list.size(), "three intervals merge")
+
+	list.MarkWritten(40, 50)
+	assert.Equal(t, 3, list.size(), "three intervals grow forward")
+
+	list.MarkWritten(50, 65)
+	assert.Equal(t, 3, list.size(), "three intervals grow backward")
+
+	list.MarkWritten(70, 80)
+	assert.Equal(t, 4, list.size(), "four intervals")
+
+	list.MarkWritten(60, 70)
+	assert.Equal(t, 3, list.size(), "three intervals merged")
+
+	list.MarkWritten(59, 71)
+	assert.Equal(t, 3, list.size(), "covered three intervals")
+
+	list.MarkWritten(5, 59)
+	assert.Equal(t, 2, list.size(), "covered two intervals")
+
+	list.MarkWritten(70, 99)
+	assert.Equal(t, 1, list.size(), "covered one intervals")
+
+}