linux-kernel - Re: [patch 14/22] memcg: fix direct softlimit reclaim to be called in limit path

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Date:	Tue, 28 Jun 2011 10:53:36 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, nishimura@....nes.nec.co.jp,
	yinghan@...gle.com, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 14/22] memcg: fix direct softlimit reclaim to be called
 in limit path

On Tue 28-06-11 17:06:49, KAMEZAWA Hiroyuki wrote:
> On Tue, 28 Jun 2011 10:08:47 +0200
> Michal Hocko <mhocko@...e.cz> wrote:
> 
> > I am sorry, that I am answering that late but I didn't get to this
> > sooner.
> > 
> > On Mon 27-06-11 16:18:12, Andrew Morton wrote:
> > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > > 
> > > commit d149e3b ("memcg: add the soft_limit reclaim in global direct
> > > reclaim") adds a softlimit hook to shrink_zones().  By this, soft limit is
> > > called as
> > > 
> > >    try_to_free_pages()
> > >        do_try_to_free_pages()
> > >            shrink_zones()
> > >                mem_cgroup_soft_limit_reclaim()
> > > 
> > > Then, direct reclaim is memcg softlimit hint aware, now.
> > > 
> > > But, the memory cgroup's "limit" path can call softlimit shrinker.
> > > 
> > >    try_to_free_mem_cgroup_pages()
> > >        do_try_to_free_pages()
> > >            shrink_zones()
> > >                mem_cgroup_soft_limit_reclaim()
> > > 
> > > This will cause a global reclaim when a memcg hits limit.
> > 
> > Sorry, I do not get it. How does it cause the global reclaim? Did you
> > mean soft reclaim?
> > 
> 
> yes. soft reclaim does global reclaim (in some means). 

But calling it global reclaim is rather confusing because in both paths
we have sc.mem_cgroup set to non-NULL which is evaluated as
!scanning_global_lru(sc). Anyway, this is not that important, I just
wanted to be sure what you meant by that comment.

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