linux-kernel - Re: [patch] memcg: skip scanning active lists based on individual size

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Message-Id: <20110901090931.c0721216.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 1 Sep 2011 09:09:31 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Johannes Weiner <jweiner@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <bsingharora@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] memcg: skip scanning active lists based on individual
 size

On Wed, 31 Aug 2011 19:13:34 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> On Wed, Aug 31, 2011 at 6:08 PM, Johannes Weiner <jweiner@...hat.com> wrote:
> > Reclaim decides to skip scanning an active list when the corresponding
> > inactive list is above a certain size in comparison to leave the
> > assumed working set alone while there are still enough reclaim
> > candidates around.
> >
> > The memcg implementation of comparing those lists instead reports
> > whether the whole memcg is low on the requested type of inactive
> > pages, considering all nodes and zones.
> >
> > This can lead to an oversized active list not being scanned because of
> > the state of the other lists in the memcg, as well as an active list
> > being scanned while its corresponding inactive list has enough pages.
> >
> > Not only is this wrong, it's also a scalability hazard, because the
> > global memory state over all nodes and zones has to be gathered for
> > each memcg and zone scanned.
> >
> > Make these calculations purely based on the size of the two LRU lists
> > that are actually affected by the outcome of the decision.
> >
> > Signed-off-by: Johannes Weiner <jweiner@...hat.com>
> > Cc: Rik van Riel <riel@...hat.com>
> > Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > Cc: Balbir Singh <bsingharora@...il.com>
> 
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
> 
> I can't understand why memcg is designed for considering all nodes and zones.
> Is it a mistake or on purpose?

It's purpose. memcg just takes care of the amount of pages.
Them, any performance numbers ?


But, hmm, this change may be good for softlimit and your work.

I'll ack when you add performance numbers in changelog.

Thanks,
-Kame

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