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

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Date:	Wed, 17 Aug 2011 13:35:50 +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>,
	"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 Wed 17-08-11 09:54:05, KAMEZAWA Hiroyuki wrote:
> On Thu, 11 Aug 2011 16:50:55 +0200
> Michal Hocko <mhocko@...e.cz> wrote:
> 
> > What about this (just compile tested)?
> > --- 
> > From: Michal Hocko <mhocko@...e.cz>
> > Subject: memcg: add nr_pages argument for hierarchical reclaim
> > 
> > Now that we are doing memcg direct reclaim limited to nr_to_reclaim
> > pages (introduced by "memcg: stop vmscan when enough done.") we have to
> > be more careful. Currently we are using SWAP_CLUSTER_MAX which is OK for
> > most callers but it might cause failures for limit resize or force_empty
> > code paths on big NUMA machines.
> > 
> > Previously we might have reclaimed up to nr_nodes * SWAP_CLUSTER_MAX
> > while now we have it at SWAP_CLUSTER_MAX. Both resize and force_empty rely
> > on reclaiming a certain amount of pages and retrying if their condition is
> > still not met.
> > 
> > Let's add nr_pages argument to mem_cgroup_hierarchical_reclaim which will
> > push it further to try_to_free_mem_cgroup_pages. We still fall back to
> > SWAP_CLUSTER_MAX for small requests so the standard code (hot) paths are not
> > affected by this.
> > 
> > Open questions:
> > - Should we care about soft limit as well? Currently I am using excess
> >   number of pages for the parameter so it can replace direct query for
> >   the value in mem_cgroup_hierarchical_reclaim but should we push it to
> >   mem_cgroup_shrink_node_zone?
> >   I do not think so because we should try to reclaim from more groups in the
> >   hierarchy and also it doesn't get to shrink_zones which has been modified
> >   by the previous patch.
> 
> 
> 
> > - 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?

> > @@ -2332,7 +2332,8 @@ static int mem_cgroup_do_charge(struct m
> >  		return CHARGE_WOULDBLOCK;
> >  
> >  	ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
> > -					      gfp_mask, flags, NULL);
> > +					      gfp_mask, flags, NULL,
> > +					      nr_pages);
> 
> Hmm, in usual, nr_pages = batch = CHARGE_BATCH = 32 ? At allocating Hugepage,
> this nr_pages will be 512 ? I think it's too big...

Yes it is. I have posted updated version already:
http://www.spinics.net/lists/linux-mm/msg23113.html

> 
> Thanks,
> -Kame

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