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

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Message-Id: <20110818085233.69dbf23b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 18 Aug 2011 08:52:33 +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 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
> > 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?
> 

How about (1 << (MAX_ORDER-1))/loop ?

Thanks,
-Kame

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