diff --git a/[refs] b/[refs]
index e04d27c9c164..ce66a39270bf 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 235772da3e2adb1f4d71f27ec5475093dd38b2ac
+refs/heads/master: 7c786059293335412f99732c6f4c2a886eab25c2
diff --git a/trunk/fs/ext4/mballoc.c b/trunk/fs/ext4/mballoc.c
index 7de0e2824436..b5235c8a2e78 100644
--- a/trunk/fs/ext4/mballoc.c
+++ b/trunk/fs/ext4/mballoc.c
@@ -635,7 +635,12 @@ static int __mb_check_buddy(struct ext4_buddy *e4b, char *file,
 #define mb_check_buddy(e4b)
 #endif
 
-/* FIXME!! need more doc */
+/*
+ * Divide blocks started from @first with length @len into
+ * smaller chunks with power of 2 blocks.
+ * Clear the bits in bitmap which the blocks of the chunk(s) covered,
+ * then increase bb_counters[] for corresponded chunk size.
+ */
 static void ext4_mb_mark_free_simple(struct super_block *sb,
 				void *buddy, ext4_grpblk_t first, ext4_grpblk_t len,
 					struct ext4_group_info *grp)