linux-kernel - Re: [PATCH v5 2/6] memcg: stop vmscan when enough done.

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Message-Id: <20110818154259.6b4adf09.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 18 Aug 2011 15:42:59 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH v5 2/6]  memcg: stop vmscan when enough done.

On Thu, 18 Aug 2011 08:27:22 +0200
Michal Hocko <mhocko@...e.cz> wrote:

> On Thu 18-08-11 08:52:33, KAMEZAWA Hiroyuki wrote:
> > On Wed, 17 Aug 2011 13:35:50 +0200
> > Michal Hocko <mhocko@...e.cz> wrote:
> > 
> > > On Wed 17-08-11 09:54:05, KAMEZAWA Hiroyuki wrote:
> > > > On Thu, 11 Aug 2011 16:50:55 +0200
> > > > > - mem_cgroup_force_empty asks for reclaiming all pages. I guess it should be
> > > > >   OK but will have to think about it some more.
> > > > 
> > > > force_empty/rmdir() is allowed to be stopped by Ctrl-C. I think passing res->usage
> > > > is overkilling.
> > > 
> > > So, how many pages should be reclaimed then?
> > > 
> > 
> > How about (1 << (MAX_ORDER-1))/loop ?
> 
> Hmm, I am not sure I see any benefit. We want to reclaim all those
> pages why shouldn't we do it in one batch? If we use a value based on
> MAX_ORDER then we make a bigger chance that force_empty fails for big
> cgroups (e.g. with a lot of page cache).

Why bigger chance to fail ? retry counter is decreased only when we cannot
make any reclaim. The number passed here is not problem against the faiulre.

I don't like very long vmscan which cannot be stopped by Ctrl-C.


> Anyway, if we want to mimic the previous behavior then we should use
> something like nr_nodes * SWAP_CLUSTER_MAX (the above value would be
> sufficient for up to 32 nodes).
> 

agreed.

Thanks,
-Kame


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