linux-kernel - Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

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Message-ID: <5069542C.2020103@parallels.com>
Date:	Mon, 1 Oct 2012 12:28:28 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Michal Hocko <mhocko@...e.cz>, <linux-kernel@...r.kernel.org>,
	<cgroups@...r.kernel.org>, <kamezawa.hiroyu@...fujitsu.com>,
	<devel@...nvz.org>, <linux-mm@...ck.org>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v3 06/13] memcg: kmem controller infrastructure

On 09/30/2012 12:25 PM, Tejun Heo wrote:
> On Fri, Sep 28, 2012 at 03:34:19PM +0400, Glauber Costa wrote:
>> On 09/27/2012 05:44 PM, Michal Hocko wrote:
>>> Anyway, I have just noticed that __mem_cgroup_try_charge does
>>> VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should
>>> keep css ref count up as well.
>>
>> IIRC, css_get will prevent the cgroup directory from being removed.
>> Because some allocations are expected to outlive the cgroup, we
>> specifically don't want that.
> 
> That synchronous ref draining is going away.  Maybe we can do that
> before kmemcg?  Michal, do you have some timeframe on mind?
> 

Since you said yourself in other points in this thread that you are fine
with some page references outliving the cgroup in the case of slab, this
is a situation that comes with the code, not a situation that was
incidentally there, and we're making use of.


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