linux-kernel - Re: [patch 08/11] mm: vmscan: convert global reclaim to per-memcg LRU lists

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Date:	Wed, 21 Sep 2011 15:57:41 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <jweiner@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <bsingharora@...il.com>,
	Ying Han <yinghan@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 08/11] mm: vmscan: convert global reclaim to per-memcg
 LRU lists

On Wed 21-09-11 15:51:43, Johannes Weiner wrote:
> On Wed, Sep 21, 2011 at 03:10:45PM +0200, Michal Hocko wrote:
> > On Mon 12-09-11 12:57:25, Johannes Weiner wrote:
[...]
> > > @@ -2451,13 +2445,24 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
> > >  static void age_active_anon(struct zone *zone, struct scan_control *sc,
> > >  			    int priority)
> > >  {
> > > -	struct mem_cgroup_zone mz = {
> > > -		.mem_cgroup = NULL,
> > > -		.zone = zone,
> > > -	};
> > > +	struct mem_cgroup *mem;
> > > +
> > > +	if (!total_swap_pages)
> > > +		return;
> > > +
> > > +	mem = mem_cgroup_iter(NULL, NULL, NULL);
> > 
> > Wouldn't be for_each_mem_cgroup more appropriate? Macro is not exported
> > but probably worth exporting? The same applies for
> > scan_zone_unevictable_pages from the previous patch.
> 
> Unfortunately, in generic code, these loops need to be layed out like
> this for !CONFIG_MEMCG to do the right thing.  mem_cgroup_iter() will
> return NULL and the loop has to execute exactly once.

Ahh, right you are. I have missed that.

> 
> This is something that will go away once we implement Christoph's
> suggestion of always having a (skeleton) root_mem_cgroup around, even
> for !CONFIG_MEMCG.

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