linux-kernel - Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging kmem

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Date:	Fri, 14 Jun 2013 14:56:13 +0400
From:	Glauber Costa <glommer@...il.com>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Michal Hocko <mhocko@...e.cz>, Tejun Heo <tj@...nel.org>,
	Glauber Costa <glommer@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH v3 5/9] memcg: use css_get/put when charging/uncharging
 kmem

On Fri, Jun 14, 2013 at 09:17:40AM +0800, Li Zefan wrote:
> >>  static void memcg_kmem_mark_dead(struct mem_cgroup *memcg)
> >>  {
> >> +	/*
> >> +	 * We need to call css_get() first, because memcg_uncharge_kmem()
> >> +	 * will call css_put() if it sees the memcg is dead.
> >> +	 */
> >> +	smb_wmb();
> >>  	if (test_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_account_flags))
> >>  		set_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_account_flags);
> > 
> > I do not feel strongly about that but maybe open coding this in
> > mem_cgroup_css_offline would be even better. There is only single caller
> > and there is smaller chance somebody will use the function incorrectly
> > later on.
> > 
> > So I leave the decision on you because this doesn't matter much.
> > 
> 
> Yeah, it should go away soon. I'll post a patch after this patchset gets
> merged into -mm tree and then we can discuss there.
 
I don't care if it is open coded or not. If there is any strong preference
from anyone on this matter, feel free to change it.
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