linux-kernel - Re: [PATCH v3 3/6] memcg: Simplify mem_cgroup_force_empty

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Message-Id: <20121029150022.a595b866.akpm@linux-foundation.org>
Date:	Mon, 29 Oct 2012 15:00:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Michal Hocko <mhocko@...e.cz>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [PATCH v3 3/6] memcg: Simplify mem_cgroup_force_empty_list
 error handling

On Mon, 29 Oct 2012 17:58:45 +0400
Glauber Costa <glommer@...allels.com> wrote:

> > + * move charges to its parent or the root cgroup if the group has no
> > + * parent (aka use_hierarchy==0).
> > + * Although this might fail (get_page_unless_zero, isolate_lru_page or
> > + * mem_cgroup_move_account fails) the failure is always temporary and
> > + * it signals a race with a page removal/uncharge or migration. In the
> > + * first case the page is on the way out and it will vanish from the LRU
> > + * on the next attempt and the call should be retried later.
> > + * Isolation from the LRU fails only if page has been isolated from
> > + * the LRU since we looked at it and that usually means either global
> > + * reclaim or migration going on. The page will either get back to the
> > + * LRU or vanish.
> 
> I just wonder for how long can it go in the worst case?

If the kernel is uniprocessor and the caller is SCHED_FIFO: ad infinitum!
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