linux-kernel - Re: [PATCH v3][0/6] memcg: prevent -ENOMEM in pre

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Message-ID: <CAOS58YNuSMjDB00UgOPjGCSFcRx-gjvMrW+e4uW0ug8WMsuFSw@mail.gmail.com>
Date:	Thu, 28 Jun 2012 09:06:25 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Han Ying <yinghan@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3][0/6] memcg: prevent -ENOMEM in pre_destroy()

Hello, KAME.

On Thu, Jun 28, 2012 at 1:33 AM, Kamezawa Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
>> Ooh, once memcg drops the __DEPRECATED_clear_css_refs, cgroup_rmdir()
>> will mark the cgroup dead before start calling pre_destroy() and none
>> of the above will happen.
>>
>
> Hm, threads which touches memcg should hold memcg's reference count rather
> than css.
> Right ? IIUC, one of reason is a reference from kswapd etc...hm. I'll check
> it.

Not sure I'm following. I meant that css_tryget() will always fail
once pre_destroy() calls being for the cgroup, so no new child or
reference can be created for it after that point.

Thanks.

-- 
tejun
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