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

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Date:	Fri, 27 Nov 2009 11:45:11 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	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>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v0 2/3] res_counter: implement thresholds

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

Thanks,
-Kame

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