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Date: Fri, 23 May 2014 14:09:48 +0200
From: Michal Hocko <mhocko@suse.cz>
To: Greg Thelen <gthelen@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Tejun Heo <tj@kernel.org>, Hugh Dickins <hughd@google.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org
Subject: Re: [PATCH] memcg: deprecate memory.force_empty knob
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On Mon 19-05-14 17:50:18, Michal Hocko wrote:
> On Mon 19-05-14 16:02:48, Michal Hocko wrote:
> > On Fri 16-05-14 15:00:16, Greg Thelen wrote:
> [...]
> > > -- First, demonstrate that just rmdir, without memory.force_empty,
> > >    temporarily hides reparented child memory stats.
> > > 
> > > $ /test
> > > p/memory.stat:rss 0
> > > p/memory.stat:total_rss 69632
> > > p/c/memory.stat:rss 69632
> > > p/c/memory.stat:total_rss 69632
> > > For a small time the p/c memory has not been reparented to p.
> > > p/memory.stat:rss 0
> > > p/memory.stat:total_rss 0
> > 
> > OK, this is a bug. Our iterators skip the children because css_tryget
> > fails on it but css_offline still not done.

Recent cgroup changes distinguish css_tryget and css_tryget_online
(http://marc.info/?l=linux-kernel&m=140025648704805). So we will only
need to use css_tryget rather than the _online variant in
__mem_cgroup_iter_next. I guess this is what Johannes was talking about.

-- 
Michal Hocko
SUSE Labs