diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 2a33306963727fba16c047610d9738b1076db38e..8af4ad12182869c4f972eeb9a5029c35e383b19a 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -490,6 +490,8 @@ pgpgin		- # of charging events to the memory cgroup. The charging
 pgpgout		- # of uncharging events to the memory cgroup. The uncharging
 		event happens each time a page is unaccounted from the cgroup.
 swap		- # of bytes of swap usage
+writeback	- # of bytes of file/anon cache that are queued for syncing to
+		disk.
 inactive_anon	- # of bytes of anonymous and swap cache memory on inactive
 		LRU list.
 active_anon	- # of bytes of anonymous and swap cache memory on active