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

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Message-ID: <508E8B95.406@parallels.com>
Date:	Mon, 29 Oct 2012 17:58:45 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.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


> 
> Changes since v1
> - use kerndoc
> - be more specific about mem_cgroup_move_parent possible failures
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Reviewed-by: Tejun Heo <tj@...nel.org>
Reviewed-by: Glauber Costa <glommer@...allels.com>

> + * 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?

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