linux-kernel - Re: [patch] memcg: pin execution to current cpu while draining stock

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Message-ID: <20110818055649.GA23056@tiehlicka.suse.cz>
Date:	Thu, 18 Aug 2011 07:56:49 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <jweiner@...hat.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, Balbir Singh <bsingharora@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] memcg: pin execution to current cpu while draining stock

On Wed 17-08-11 21:49:27, Johannes Weiner wrote:
> Commit d1a05b6 'memcg: do not try to drain per-cpu caches without
> pages' added a drain_local_stock() call to a preemptible section.
> 
> The draining task looks up the cpu-local stock twice to set the
> draining-flag, then to drain the stock and clear the flag again.  If
> the task is migrated to a different CPU in between, noone will clear
> the flag on the first stock and it will be forever undrainable.  Its
> charge can not be recovered and the cgroup can not be deleted anymore.
> 
> Properly pin the task to the executing CPU while draining stocks.
> 
> Signed-off-by: Johannes Weiner <jweiner@...hat.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com
> Cc: Michal Hocko <mhocko@...e.cz>

My fault, I didn't realize that drain_local_stock needs preemption
disabled. Sorry about that and good work, Johannes. 

Acked-by: Michal Hocko <mhocko@...e.cz>
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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