linux-kernel - Re: [PATCH RFC v0 2/3] res_counter: implement thresholds

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Date:	Fri, 27 Nov 2009 09:08:19 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <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>,
	Pavel Emelyanov <xemul@...nvz.org>,
	linux-kernel@...r.kernel.org, Dan Malek <dan@...eddedalley.com>,
	Vladislav Buzov <vbuzov@...eddedalley.com>
Subject: Re: [PATCH RFC v0 2/3] res_counter: implement thresholds

On Fri, Nov 27, 2009 at 5:08 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> On Fri, Nov 27, 2009 at 8:15 AM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
>> On Fri, 27 Nov 2009 09:20:35 +0900
>> Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
>>
>>> Hi.
>>> >
>>> > @@ -73,6 +76,7 @@ void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
>>> >             val = counter->usage;
>>> >
>>> >     counter->usage -= val;
>>> > +   res_counter_threshold_notify_locked(counter);
>>> >  }
>>> >
>>> hmm.. this adds new checks to hot-path of process life cycle.
>>>
>>> Do you have any number on performance impact of these patches(w/o setting any threshold)?

No, I don't. I did only functional testing on this stage.

>>> IMHO, it might be small enough to be ignored because KAMEZAWA-san's coalesce charge/uncharge
>>> patches have decreased charge/uncharge for res_counter itself, but I want to know just to make sure.
>>>
>> Another concern is to support root cgroup, you need another notifier hook in
>> memcg because root cgroup doesn't use res_counter now.
>>
>> Can't this be implemented in a way like softlimit check ?

I'll investigate it.

>> Filter by the number of event will be good for notifier behavior, for avoiding
>> too much wake up, too.

Good idea, thanks.

> I guess the semantics would vary then, they would become activity
> semantics. I think we should avoid threshold notification for root,
> since we have no limits in root anymore.

Threshold notifications for root cgroup is really needed on embedded
systems to avid OOM-killer.

>
> BTW, Kirill, I've been meaning to write this layer on top of
> cgroupstats, is there anything that prevents us from using that today?

I'll investigate it.

> CC'ing Dan Malek and Vladslav Buzov who worked on similar patches
> earlier.
>
> Balbir Singh.
>
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