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 <yinghan@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 8058273e04a0a9272efae676d770752870f319ef..8e19065c9a1938c4216e89b7155f15b4354083bf 100644 (file)
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -428,8 +428,11 @@ 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.