diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9183f9c..d8da538 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4034,6 +4034,8 @@
 	return nr;
 }
 
+#define EXTENT_SIZE_PER_ITEM	(256 * 1024)
+
 /*
  * shrink metadata reservation for delalloc
  */
@@ -4050,6 +4052,10 @@
 	int loops;
 	enum btrfs_reserve_flush_enum flush;
 
+	/* Calc the number of the pages we need flush for space reservation */
+	to_reclaim = calc_reclaim_items_nr(root, to_reclaim);
+	to_reclaim *= EXTENT_SIZE_PER_ITEM;
+
 	trans = (struct btrfs_trans_handle *)current->journal_info;
 	block_rsv = &root->fs_info->delalloc_block_rsv;
 	space_info = block_rsv->space_info;