linux-kernel - Re: cgroup: real meaning of memory.usage_in

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Message-ID: <20110323142645.GB15474@tiehlicka.suse.cz>
Date:	Wed, 23 Mar 2011 15:26:45 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Ying Han <yinghan@...gle.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: cgroup: real meaning of memory.usage_in_bytes

On Tue 22-03-11 10:06:27, Ying Han wrote:
> On Tue, Mar 22, 2011 at 12:35 AM, Michal Hocko <mhocko@...e.cz> wrote:
> > On Mon 21-03-11 10:22:41, Ying Han wrote:
> > [...]
> >>
> >> Michal,
> >>
> >> Can you help to post the test result after applying the patch?
> >
> > The result of the LTP test is:
> > TEST 4: MEMORY CONTROLLER TESTING
> > RUNNING SETUP.....
> > WARN:/dev/memctl already exist..overwriting
> > Cleanup called
> > TEST STARTED: Please avoid using system while this test executes
> > memory usage from memory.usage_in_bytes= 62955520
> > memory usage from memory.stat= 62955520
> > TINFO ? Memory Resource Controller: stat check test passes first run
> > Test continues to run the second step.
> > memory usage from memory.usage_in_bytes= 78643200
> > memory usage from memory.stat=78643200
> > TPASS ? Memory Resource Controller: stat check test PASSED
> > Memory Resource Controller test executed successfully.
> > Cleanup called
[...]
> Thanks Michal for fixing it up. Regardless of the performance
> overhead, the change make sense to me.

As you can see in the other email in this thread the patch is not 100%
correct because it doesn't consider batched uncharges which are stored
in the task_struct. Make it 100% correct would be harder and probably
not worth the overhead. Daisuke Nishimura is working on the
documentation update patch which will most likely describe that
usage_in_bytes is not exactly rss+cache and that nobody should rely on
it.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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