linux-kernel - Re: [PATCH v4 3/5] memcg : stop scanning if enough

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Message-ID: <20110801194905.GA5354@tiehlicka.suse.cz>
Date:	Mon, 1 Aug 2011 21:49:42 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH v4 3/5] memcg : stop scanning if enough

On Mon 01-08-11 16:37:45, Michal Hocko wrote:
> On Wed 27-07-11 14:49:00, KAMEZAWA Hiroyuki wrote:
> > memcg :avoid node fallback scan if possible.
> > 
> > Now, try_to_free_pages() scans all zonelist because the page allocator
> > should visit all zonelists...but that behavior is harmful for memcg.
> > Memcg just scans memory because it hits limit...no memory shortage
> > in pased zonelist.
> > 
> > For example, with following unbalanced nodes
> > 
> >      Node 0    Node 1
> > File 1G        0
> > Anon 200M      200M
> > 
> > memcg will cause swap-out from Node1 at every vmscan.
> > 
> > Another example, assume 1024 nodes system.
> > With 1024 node system, memcg will visit 1024 nodes
> > pages per vmscan... This is overkilling. 
> > 
> > This is why memcg's victim node selection logic doesn't work
> > as expected.
> 
> Previous patch adds nodemask filled by
> mem_cgroup_select_victim_node. Shouldn't we rather limit that nodemask
> to a victim node?

Bahh, scratch that. I was jumping from one thing to another and got 
totally confused. Victim memcg is not bound to any particular node in 
general...
Sorry for noise. I will try to get back to this tomorrow.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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