[PATCH] memcg: update documentation to describe usage_in_bytes

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Mon, 28 Mar 2011 08:55:08 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> > > Considering more, without these files, we cannot know the actual usage of
> > > a res_counter, although we set a limit to a res_counter. So, I want to keep
> > > these files.
> > > 
> > > If no-one have any objections, I'll prepare a patch to update the documentation.
> > > 
> > 
> > please.
> > 
> I'm sorry for my late response. I've been out of office because of a cold.
> I'll prepare the patch later.
> 
How about this ?

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

Update the meaning of *.usage_in_bytes. They doesn't show the actual usage of
RSS+Cache(+Swap). They show the res_counter->usage for memory and memory+swap.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 Documentation/cgroups/memory.txt |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 7781857..ab7d4c1 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -52,8 +52,10 @@ Brief summary of control files.
  tasks				 # attach a task(thread) and show list of threads
  cgroup.procs			 # show list of processes
  cgroup.event_control		 # an interface for event_fd()
- memory.usage_in_bytes		 # show current memory(RSS+Cache) usage.
- memory.memsw.usage_in_bytes	 # show current memory+Swap usage
+ memory.usage_in_bytes		 # show current res_counter usage for memory
+				 (See 5.5 for details)
+ memory.memsw.usage_in_bytes	 # show current res_counter usage for memory+Swap
+				 (See 5.5 for details)
  memory.limit_in_bytes		 # set/show limit of memory usage
  memory.memsw.limit_in_bytes	 # set/show limit of memory+Swap usage
  memory.failcnt			 # show the number of memory usage hits limits
@@ -453,6 +455,16 @@ memory under it will be reclaimed.
 You can reset failcnt by writing 0 to failcnt file.
 # echo 0 > .../memory.failcnt
 
+5.5 usage_in_bytes
+
+As described in 2.1, memory cgroup uses res_counter for tracking and limiting
+the memory usage. memory.usage_in_bytes shows the current res_counter usage for
+memory, and DOESN'T show a actual usage of RSS and Cache. It is usually bigger
+than the actual usage for a performance improvement reason. If you want to know
+the actual usage, you can use memory.stat(see 5.2).
+It's the same for memory.memsw.usage_in_bytes, which shows the current
+res_counter usage for memory+swap.
+
 6. Hierarchy support
 
 The memory controller supports a deep hierarchy and hierarchical accounting.
-- 
1.7.1

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