From: Michal Hocko <mhocko@suse.cz>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] memcg: update documentation to describe usage_in_bytes
Date: Mon, 28 Mar 2011 11:48:20 +0200 [thread overview]
Message-ID: <20110328094820.GC5693@tiehlicka.suse.cz> (raw)
In-Reply-To: <20110328181127.b8a2a1c5.kamezawa.hiroyu@jp.fujitsu.com>
On Mon 28-03-11 18:11:27, KAMEZAWA Hiroyuki wrote:
> On Mon, 28 Mar 2011 09:43:42 +0200
> Michal Hocko <mhocko@suse.cz> wrote:
>
> > On Mon 28-03-11 13:25:50, Daisuke Nishimura wrote:
> > > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
[...]
> > > +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.
> >
> > Isn't an explicit mention about caching charges better?
> >
>
> It's difficult to distinguish which is spec. and which is implemnation details...
Sure. At least commit log should contain the implementation details IMO,
though.
>
> My one here ;)
> ==
> 5.5 usage_in_bytes
>
> For efficiency, as other kernel components, memory cgroup uses some optimization to
> avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the
> method and doesn't show 'exact' value of usage, it's an fuzz value for efficient
> access. (Of course, when necessary, it's synchronized.)
> In usual, the value (RSS+CACHE) in memory.stat shows more exact value. IOW,
- In usual, the value (RSS+CACHE) in memory.stat shows more exact value. IOW,
+ (RSS+CACHE) value from memory.stat shows more exact value and should be used
+ by userspace. IOW,
?
> usage_in_bytes is less exact than memory.stat. The error will be larger on the larger
> hardwares which have many cpus and tasks.
> ==
>
> Hmm ?
Looks much better.
Thanks
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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next prev parent reply other threads:[~2011-03-28 9:48 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-18 15:25 cgroup: real meaning of memory.usage_in_bytes Michal Hocko
2011-03-18 15:29 ` Michal Hocko
2011-03-21 9:34 ` Michal Hocko
2011-03-21 10:24 ` [PATCH] memcg: consider per-cpu stock reserves when returning RES_USAGE for _MEM Michal Hocko
2011-03-22 0:10 ` KAMEZAWA Hiroyuki
2011-03-22 1:47 ` Daisuke Nishimura
2011-03-22 7:31 ` Michal Hocko
2011-03-23 0:27 ` Daisuke Nishimura
2011-03-23 4:35 ` KAMEZAWA Hiroyuki
2011-03-27 23:55 ` Daisuke Nishimura
2011-03-28 4:25 ` [PATCH] memcg: update documentation to describe usage_in_bytes Daisuke Nishimura
2011-03-28 7:43 ` Michal Hocko
2011-03-28 9:11 ` KAMEZAWA Hiroyuki
2011-03-28 9:48 ` Michal Hocko [this message]
2011-03-28 10:31 ` KAMEZAWA Hiroyuki
2011-03-29 1:15 ` [PATCH v2] " Daisuke Nishimura
2011-03-29 1:24 ` KAMEZAWA Hiroyuki
2011-03-29 7:21 ` Michal Hocko
2011-04-19 12:14 ` Michal Hocko
2011-04-19 23:24 ` Daisuke Nishimura
2011-03-21 17:22 ` cgroup: real meaning of memory.usage_in_bytes Ying Han
2011-03-22 7:35 ` Michal Hocko
2011-03-22 17:06 ` Ying Han
2011-03-23 14:26 ` Michal Hocko
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