linux-kernel - Re: [PATCH RFC v2 3/4] memcg: rework usage of stats by soft limit

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Date:	Sat, 12 Dec 2009 15:06:52 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	nishimura@....nes.nec.co.jp
Cc:	containers@...ts.linux-foundation.org, linux-mm@...ck.org,
	Paul Menage <menage@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Dan Malek <dan@...eddedalley.com>,
	Vladislav Buzov <vbuzov@...eddedalley.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 3/4] memcg: rework usage of stats by soft limit

On Sat, Dec 12, 2009 at 5:50 AM, Daisuke Nishimura
<d-nishimura@....biglobe.ne.jp> wrote:
> Sorry, I disagree this change.
>
> mem_cgroup_soft_limit_check() is used for checking how much current usage exceeds
> the soft_limit_in_bytes and updating softlimit tree asynchronously, instead of
> checking every charge/uncharge. What if you change the soft_limit_in_bytes,
> but the number of charges and uncharges are very balanced afterwards ?
> The softlimit tree will not be updated for a long time.

I don't see how my patch affects the logic you've described.
Statistics updates and
checks in the same place. It just uses decrement instead of increment.

>
> And IIUC, it's the same for your threshold feature, right ?
> I think it would be better:
>
> - discard this change.
> - in 4/4, rename mem_cgroup_soft_limit_check to mem_cgroup_event_check,
>  and instead of adding a new STAT counter, do like:
>
>        if (mem_cgroup_event_check(mem)) {
>                mem_cgroup_update_tree(mem, page);
>                mem_cgroup_threshold(mem);
>        }

I think that mem_cgroup_update_tree() and mem_cgroup_threshold() should be
run with different frequency. How to share MEM_CGROUP_STAT_EVENTS
between soft limits and thresholds in this case?
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