diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index b90cd37..1bf2ff5 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -17,6 +17,7 @@
  */
 
 #include <linux/vmalloc.h>
+#include <linux/rbtree.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "backref.h"
@@ -34,6 +35,266 @@ struct extent_inode_elem {
 	struct extent_inode_elem *next;
 };
 
+/*
+ * ref_root is used as the root of the ref tree that hold a collection
+ * of unique references.
+ */
+struct ref_root {
+	struct rb_root rb_root;
+
+	/*
+	 * The unique_refs represents the number of ref_nodes with a positive
+	 * count stored in the tree. Even if a ref_node(the count is greater
+	 * than one) is added, the unique_refs will only increase one.
+	 */
+	unsigned int unique_refs;
+};
+
+/* ref_node is used to store a unique reference to the ref tree. */
+struct ref_node {
+	struct rb_node rb_node;
+
+	/* For NORMAL_REF, otherwise all these fields should be set to 0 */
+	u64 root_id;
+	u64 object_id;
+	u64 offset;
+
+	/* For SHARED_REF, otherwise parent field should be set to 0 */
+	u64 parent;
+
+	/* Ref to the ref_mod of btrfs_delayed_ref_node(delayed-ref.h) */
+	int ref_mod;
+};
+
+/* Dynamically allocate and initialize a ref_root */
+static struct ref_root *ref_root_alloc(void)
+{
+	struct ref_root *ref_tree;
+
+	ref_tree = kmalloc(sizeof(*ref_tree), GFP_NOFS);
+	if (!ref_tree)
+		return NULL;
+
+	ref_tree->rb_root = RB_ROOT;
+	ref_tree->unique_refs = 0;
+
+	return ref_tree;
+}
+
+/* Free all nodes in the ref tree, and reinit ref_root */
+static void ref_root_fini(struct ref_root *ref_tree)
+{
+	struct ref_node *node;
+	struct rb_node *next;
+
+	while ((next = rb_first(&ref_tree->rb_root)) != NULL) {
+		node = rb_entry(next, struct ref_node, rb_node);
+		rb_erase(next, &ref_tree->rb_root);
+		kfree(node);
+	}
+
+	ref_tree->rb_root = RB_ROOT;
+	ref_tree->unique_refs = 0;
+}
+
+/* Free dynamically allocated ref_root */
+static void ref_root_free(struct ref_root *ref_tree)
+{
+	if (!ref_tree)
+		return;
+
+	ref_root_fini(ref_tree);
+	kfree(ref_tree);
+}
+
+/*
+ * Compare ref_node with (root_id, object_id, offset, parent)
+ *
+ * The function compares the two ref_node a and b. It returns an integer less
+ * than, equal to, or greater than zero , respectively, to be less than, to
+ * equal, or be greater than b.
+ */
+static int ref_node_cmp(struct ref_node *a, struct ref_node *b)
+{
+	if (a->root_id < b->root_id)
+		return -1;
+	else if (a->root_id > b->root_id)
+		return 1;
+
+	if (a->object_id < b->object_id)
+		return -1;
+	else if (a->object_id > b->object_id)
+		return 1;
+
+	if (a->offset < b->offset)
+		return -1;
+	else if (a->offset > b->offset)
+		return 1;
+
+	if (a->parent < b->parent)
+		return -1;
+	else if (a->parent > b->parent)
+		return 1;
+
+	return 0;
+}
+
+/*
+ * Search ref_node with (root_id, object_id, offset, parent) in the tree
+ *
+ * if found, the pointer of the ref_node will be returned;
+ * if not found, NULL will be returned and pos will point to the rb_node for
+ * insert, pos_parent will point to pos'parent for insert;
+*/
+static struct ref_node *__ref_tree_search(struct ref_root *ref_tree,
+					  struct rb_node ***pos,
+					  struct rb_node **pos_parent,
+					  u64 root_id, u64 object_id,
+					  u64 offset, u64 parent)
+{
+	struct ref_node *cur = NULL;
+	struct ref_node entry;
+	int ret;
+
+	entry.root_id = root_id;
+	entry.object_id = object_id;
+	entry.offset = offset;
+	entry.parent = parent;
+
+	*pos = &ref_tree->rb_root.rb_node;
+
+	while (**pos) {
+		*pos_parent = **pos;
+		cur = rb_entry(*pos_parent, struct ref_node, rb_node);
+
+		ret = ref_node_cmp(cur, &entry);
+		if (ret > 0)
+			*pos = &(**pos)->rb_left;
+		else if (ret < 0)
+			*pos = &(**pos)->rb_right;
+		else
+			return cur;
+	}
+
+	return NULL;
+}
+
+/*
+ * Insert a ref_node to the ref tree
+ * @pos used for specifiy the position to insert
+ * @pos_parent for specifiy pos's parent
+ *
+ * success, return 0;
+ * ref_node already exists, return -EEXIST;
+*/
+static int ref_tree_insert(struct ref_root *ref_tree, struct rb_node **pos,
+			   struct rb_node *pos_parent, struct ref_node *ins)
+{
+	struct rb_node **p = NULL;
+	struct rb_node *parent = NULL;
+	struct ref_node *cur = NULL;
+
+	if (!pos) {
+		cur = __ref_tree_search(ref_tree, &p, &parent, ins->root_id,
+					ins->object_id, ins->offset,
+					ins->parent);
+		if (cur)
+			return -EEXIST;
+	} else {
+		p = pos;
+		parent = pos_parent;
+	}
+
+	rb_link_node(&ins->rb_node, parent, p);
+	rb_insert_color(&ins->rb_node, &ref_tree->rb_root);
+
+	return 0;
+}
+
+/* Erase and free ref_node, caller should update ref_root->unique_refs */
+static void ref_tree_remove(struct ref_root *ref_tree, struct ref_node *node)
+{
+	rb_erase(&node->rb_node, &ref_tree->rb_root);
+	kfree(node);
+}
+
+/*
+ * Update ref_root->unique_refs
+ *
+ * Call __ref_tree_search
+ *	1. if ref_node doesn't exist, ref_tree_insert this node, and update
+ *	ref_root->unique_refs:
+ *		if ref_node->ref_mod > 0, ref_root->unique_refs++;
+ *		if ref_node->ref_mod < 0, do noting;
+ *
+ *	2. if ref_node is found, then get origin ref_node->ref_mod, and update
+ *	ref_node->ref_mod.
+ *		if ref_node->ref_mod is equal to 0,then call ref_tree_remove
+ *
+ *		according to origin_mod and new_mod, update ref_root->items
+ *		+----------------+--------------+-------------+
+ *		|		 |new_count <= 0|new_count > 0|
+ *		+----------------+--------------+-------------+
+ *		|origin_count < 0|       0      |      1      |
+ *		+----------------+--------------+-------------+
+ *		|origin_count > 0|      -1      |      0      |
+ *		+----------------+--------------+-------------+
+ *
+ * In case of allocation failure, -ENOMEM is returned and the ref_tree stays
+ * unaltered.
+ * Success, return 0
+ */
+static int ref_tree_add(struct ref_root *ref_tree, u64 root_id, u64 object_id,
+			u64 offset, u64 parent, int count)
+{
+	struct ref_node *node = NULL;
+	struct rb_node **pos = NULL;
+	struct rb_node *pos_parent = NULL;
+	int origin_count;
+	int ret;
+
+	if (!count)
+		return 0;
+
+	node = __ref_tree_search(ref_tree, &pos, &pos_parent, root_id,
+				 object_id, offset, parent);
+	if (node == NULL) {
+		node = kmalloc(sizeof(*node), GFP_NOFS);
+		if (!node)
+			return -ENOMEM;
+
+		node->root_id = root_id;
+		node->object_id = object_id;
+		node->offset = offset;
+		node->parent = parent;
+		node->ref_mod = count;
+
+		ret = ref_tree_insert(ref_tree, pos, pos_parent, node);
+		ASSERT(!ret);
+		if (ret) {
+			kfree(node);
+			return ret;
+		}
+
+		ref_tree->unique_refs += node->ref_mod > 0 ? 1 : 0;
+
+		return 0;
+	}
+
+	origin_count = node->ref_mod;
+	node->ref_mod += count;
+
+	if (node->ref_mod > 0)
+		ref_tree->unique_refs += origin_count > 0 ? 0 : 1;
+	else if (node->ref_mod <= 0)
+		ref_tree->unique_refs += origin_count > 0 ? -1 : 0;
+
+	if (!node->ref_mod)
+		ref_tree_remove(ref_tree, node);
+
+	return 0;
+}
+
 static int check_extent_in_eb(struct btrfs_key *key, struct extent_buffer *eb,
 				struct btrfs_file_extent_item *fi,
 				u64 extent_item_pos,
@@ -703,6 +964,7 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
 static int __add_inline_refs(struct btrfs_fs_info *fs_info,
 			     struct btrfs_path *path, u64 bytenr,
 			     int *info_level, struct list_head *prefs,
+			     struct ref_root *ref_tree,
 			     u64 *total_refs, u64 inum)
 {
 	int ret = 0;
@@ -770,6 +1032,13 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
 			count = btrfs_shared_data_ref_count(leaf, sdref);
 			ret = __add_prelim_ref(prefs, 0, NULL, 0, offset,
 					       bytenr, count, GFP_NOFS);
+			if (ref_tree) {
+				if (!ret)
+					ret = ref_tree_add(ref_tree, 0, 0, 0,
+							   bytenr, count);
+				if (!ret && ref_tree->unique_refs > 1)
+					ret = BACKREF_FOUND_SHARED;
+			}
 			break;
 		}
 		case BTRFS_TREE_BLOCK_REF_KEY:
@@ -797,6 +1066,15 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
 			root = btrfs_extent_data_ref_root(leaf, dref);
 			ret = __add_prelim_ref(prefs, root, &key, 0, 0,
 					       bytenr, count, GFP_NOFS);
+			if (ref_tree) {
+				if (!ret)
+					ret = ref_tree_add(ref_tree, root,
+							   key.objectid,
+							   key.offset, 0,
+							   count);
+				if (!ret && ref_tree->unique_refs > 1)
+					ret = BACKREF_FOUND_SHARED;
+			}
 			break;
 		}
 		default:
@@ -815,7 +1093,8 @@ static int __add_inline_refs(struct btrfs_fs_info *fs_info,
  */
 static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
 			    struct btrfs_path *path, u64 bytenr,
-			    int info_level, struct list_head *prefs, u64 inum)
+			    int info_level, struct list_head *prefs,
+			    struct ref_root *ref_tree, u64 inum)
 {
 	struct btrfs_root *extent_root = fs_info->extent_root;
 	int ret;
@@ -858,6 +1137,13 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
 			count = btrfs_shared_data_ref_count(leaf, sdref);
 			ret = __add_prelim_ref(prefs, 0, NULL, 0, key.offset,
 						bytenr, count, GFP_NOFS);
+			if (ref_tree) {
+				if (!ret)
+					ret = ref_tree_add(ref_tree, 0, 0, 0,
+							   bytenr, count);
+				if (!ret && ref_tree->unique_refs > 1)
+					ret = BACKREF_FOUND_SHARED;
+			}
 			break;
 		}
 		case BTRFS_TREE_BLOCK_REF_KEY:
@@ -886,6 +1172,15 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
 			root = btrfs_extent_data_ref_root(leaf, dref);
 			ret = __add_prelim_ref(prefs, root, &key, 0, 0,
 					       bytenr, count, GFP_NOFS);
+			if (ref_tree) {
+				if (!ret)
+					ret = ref_tree_add(ref_tree, root,
+							   key.objectid,
+							   key.offset, 0,
+							   count);
+				if (!ret && ref_tree->unique_refs > 1)
+					ret = BACKREF_FOUND_SHARED;
+			}
 			break;
 		}
 		default:
@@ -912,13 +1207,16 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
  * commit root.
  * The special case is for qgroup to search roots in commit_transaction().
  *
+ * If check_shared is set to 1, any extent has more than one ref item, will
+ * be returned BACKREF_FOUND_SHARED immediately.
+ *
  * FIXME some caching might speed things up
  */
 static int find_parent_nodes(struct btrfs_trans_handle *trans,
 			     struct btrfs_fs_info *fs_info, u64 bytenr,
 			     u64 time_seq, struct ulist *refs,
 			     struct ulist *roots, const u64 *extent_item_pos,
-			     u64 root_objectid, u64 inum)
+			     u64 root_objectid, u64 inum, int check_shared)
 {
 	struct btrfs_key key;
 	struct btrfs_path *path;
@@ -930,6 +1228,7 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 	struct list_head prefs;
 	struct __prelim_ref *ref;
 	struct extent_inode_elem *eie = NULL;
+	struct ref_root *ref_tree = NULL;
 	u64 total_refs = 0;
 
 	INIT_LIST_HEAD(&prefs);
@@ -961,6 +1260,18 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans,
 again:
 	head = NULL;
 
+	if (check_shared) {
+		if (!ref_tree) {
+			ref_tree = ref_root_alloc();
+			if (!ref_tree) {
+				ret = -ENOMEM;
+				goto out;
+			}
+		} else {
+			ref_root_fini(ref_tree);
+		}
+	}
+
 	ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
 	if (ret < 0)
 		goto out;
@@ -1005,6 +1316,36 @@ again:
 		} else {
 			spin_unlock(&delayed_refs->lock);
 		}
+
+		if (check_shared && !list_empty(&prefs_delayed)) {
+			/*
+			 * Add all delay_ref to the ref_tree and check if there
+			 * are multiple ref items added.
+			 */
+			list_for_each_entry(ref, &prefs_delayed, list) {
+				if (ref->key_for_search.type) {
+					ret = ref_tree_add(ref_tree,
+						ref->root_id,
+						ref->key_for_search.objectid,
+						ref->key_for_search.offset,
+						0, ref->count);
+					if (ret)
+						goto out;
+				} else {
+					ret = ref_tree_add(ref_tree, 0, 0, 0,
+						     ref->parent, ref->count);
+					if (ret)
+						goto out;
+				}
+
+			}
+
+			if (ref_tree->unique_refs > 1) {
+				ret = BACKREF_FOUND_SHARED;
+				goto out;
+			}
+
+		}
 	}
 
 	if (path->slots[0]) {
@@ -1020,11 +1361,13 @@ again:
 		     key.type == BTRFS_METADATA_ITEM_KEY)) {
 			ret = __add_inline_refs(fs_info, path, bytenr,
 						&info_level, &prefs,
-						&total_refs, inum);
+						ref_tree, &total_refs,
+						inum);
 			if (ret)
 				goto out;
 			ret = __add_keyed_refs(fs_info, path, bytenr,
-					       info_level, &prefs, inum);
+					       info_level, &prefs,
+					       ref_tree, inum);
 			if (ret)
 				goto out;
 		}
@@ -1109,6 +1452,7 @@ again:
 
 out:
 	btrfs_free_path(path);
+	ref_root_free(ref_tree);
 	while (!list_empty(&prefs)) {
 		ref = list_first_entry(&prefs, struct __prelim_ref, list);
 		list_del(&ref->list);
@@ -1162,8 +1506,8 @@ static int btrfs_find_all_leafs(struct btrfs_trans_handle *trans,
 	if (!*leafs)
 		return -ENOMEM;
 
-	ret = find_parent_nodes(trans, fs_info, bytenr,
-				time_seq, *leafs, NULL, extent_item_pos, 0, 0);
+	ret = find_parent_nodes(trans, fs_info, bytenr, time_seq,
+				*leafs, NULL, extent_item_pos, 0, 0, 0);
 	if (ret < 0 && ret != -ENOENT) {
 		free_leaf_list(*leafs);
 		return ret;
@@ -1205,8 +1549,8 @@ static int __btrfs_find_all_roots(struct btrfs_trans_handle *trans,
 
 	ULIST_ITER_INIT(&uiter);
 	while (1) {
-		ret = find_parent_nodes(trans, fs_info, bytenr,
-					time_seq, tmp, *roots, NULL, 0, 0);
+		ret = find_parent_nodes(trans, fs_info, bytenr, time_seq,
+					tmp, *roots, NULL, 0, 0, 0);
 		if (ret < 0 && ret != -ENOENT) {
 			ulist_free(tmp);
 			ulist_free(*roots);
@@ -1276,7 +1620,7 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
 	ULIST_ITER_INIT(&uiter);
 	while (1) {
 		ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
-					roots, NULL, root_objectid, inum);
+					roots, NULL, root_objectid, inum, 1);
 		if (ret == BACKREF_FOUND_SHARED) {
 			/* this is the only condition under which we return 1 */
 			ret = 1;
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 2e7c97a..31a174a 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -20,6 +20,7 @@
 #include "locking.h"
 #include "rcu-string.h"
 #include "backref.h"
+#include "transaction.h"
 
 static struct kmem_cache *extent_state_cache;
 static struct kmem_cache *extent_buffer_cache;
@@ -4498,21 +4499,36 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			flags |= (FIEMAP_EXTENT_DELALLOC |
 				  FIEMAP_EXTENT_UNKNOWN);
 		} else if (fieinfo->fi_extents_max) {
+			struct btrfs_trans_handle *trans;
+
 			u64 bytenr = em->block_start -
 				(em->start - em->orig_start);
 
 			disko = em->block_start + offset_in_extent;
 
 			/*
+			 * We need a trans handle to get delayed refs
+			 */
+			trans = btrfs_join_transaction(root);
+			/*
+			 * It's OK if we can't start a trans
+			 * we can still check from commit_root
+			 */
+			if (IS_ERR(trans))
+				trans = NULL;
+
+			/*
 			 * As btrfs supports shared space, this information
 			 * can be exported to userspace tools via
 			 * flag FIEMAP_EXTENT_SHARED.  If fi_extents_max == 0
 			 * then we're just getting a count and we can skip the
 			 * lookup stuff.
 			 */
-			ret = btrfs_check_shared(NULL, root->fs_info,
+			ret = btrfs_check_shared(trans, root->fs_info,
 						 root->objectid,
 						 btrfs_ino(inode), bytenr);
+			if (trans)
+				btrfs_end_transaction(trans, root);
 			if (ret < 0)
 				goto out_free;
 			if (ret)
