linux-kernel - Re: [PATCH] memcg, oom: lock mem_cgroup_print_oom

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Date:	Thu, 12 Dec 2013 15:31:51 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg, oom: lock mem_cgroup_print_oom_info

On Thu, 12 Dec 2013, Michal Hocko wrote:

> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index 28c9221b74ea..c72b03bf9679 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -1647,13 +1647,13 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
> > >   */
> > >  void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
> > >  {
> > > -	struct cgroup *task_cgrp;
> > > -	struct cgroup *mem_cgrp;
> > >  	/*
> > > -	 * Need a buffer in BSS, can't rely on allocations. The code relies
> > > -	 * on the assumption that OOM is serialized for memory controller.
> > > -	 * If this assumption is broken, revisit this code.
> > > +	 * protects memcg_name and makes sure that parallel ooms do not
> > > +	 * interleave
> > 
> > Parallel memcg oom kills can happen in disjoint memcg hierarchies, this 
> > just prevents the printing of the statistics from interleaving.  I'm not 
> > sure if that's clear from this comment.
> 
> What about this instead:
> 	* Protects memcg_name and makes sure that ooms from parallel
> 	* hierarchies do not interleave.
> ?

I think it would be better to explicitly say that you're referring only to 
the printing here and that we're ensuring it does not interleave in the 
kernel log.
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