linux-kernel - Re: [patch v2 3/6] memcg: rework mem_cgroup

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Date:	Tue, 11 Dec 2012 16:54:32 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Ying Han <yinghan@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <htejun@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [patch v2 3/6] memcg: rework mem_cgroup_iter to use cgroup
 iterators

On Sun 09-12-12 11:39:50, Ying Han wrote:
> On Mon, Nov 26, 2012 at 10:47 AM, Michal Hocko <mhocko@...e.cz> wrote:
[...]
> >                 if (reclaim) {
> > -                       iter->position = id;
> > +                       struct mem_cgroup *curr = memcg;
> > +
> > +                       if (last_visited)
> > +                               css_put(&last_visited->css);
			    ^^^^^^^^^^^
			    here
> > +
> > +                       if (css && !memcg)
> > +                               curr = mem_cgroup_from_css(css);
> > +
> > +                       /* make sure that the cached memcg is not removed */
> > +                       if (curr)
> > +                               css_get(&curr->css);
> > +                       iter->last_visited = curr;
> 
> Here we take extra refcnt for last_visited, and assume it is under
> target reclaim which then calls mem_cgroup_iter_break() and we leaked
> a refcnt of the target memcg css.

I think you are not right here. The extra reference is kept for
iter->last_visited and it will be dropped the next time somebody sees
the same zone-priority iter. See above.

Or have I missed your question?

[...]
-- 
Michal Hocko
SUSE Labs
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