memcg: fix pgpgin/pgpgout documentation

The two memcg stats pgpgin/pgpgout have different meaning than the ones
in vmstat, which indicates that we picked a bad naming for them.

It might be late to change the stat name, but better documentation is
always helpful.

Signed-off-by: Ying Han <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index c7de7dac43b51779260f3ae08e39baa9cbeb6ac3..4c95c0034a4bbbffdae12a99ff2ddbd0798ca09c 100644 (file)
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -410,8 +410,11 @@ memory.stat file includes following statistics
 cache          - # of bytes of page cache memory.
 rss            - # of bytes of anonymous and swap cache memory.
 mapped_file    - # of bytes of mapped file (includes tmpfs/shmem)
-pgpgin         - # of pages paged in (equivalent to # of charging events).
-pgpgout                - # of pages paged out (equivalent to # of uncharging events).
+pgpgin         - # of charging events to the memory cgroup. The charging
+               event happens each time a page is accounted as either mapped
+               anon page(RSS) or cache page(Page Cache) to the cgroup.
+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
 inactive_anon  - # of bytes of anonymous memory and swap cache memory on
                LRU list.