[PATCH] memcg: fix the document of pgpgin/pgpgout

[Ying Han <yinghan@google.com>]

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>
---
 Documentation/cgroups/memory.txt |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index cc0ebc5..eb6a911 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -386,8 +386,11 @@ 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.
-- 
1.7.3.1

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