linux-kernel - Re: [PATCH v2 09/11] memcg: propagate kmem limiting information to children

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Date:	Fri, 17 Aug 2012 14:39:23 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <devel@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v2 09/11] memcg: propagate kmem limiting information to
 children

On 08/17/2012 02:35 PM, Michal Hocko wrote:
> On Fri 17-08-12 14:07:00, Glauber Costa wrote:
>> On 08/17/2012 01:35 PM, Michal Hocko wrote:
>>>>> Above you said "Once enabled, can't be disabled." and now you can
>>>>>>> disable it? Say you are a leaf group with non accounted parents. This
>>>>>>> will clear the flag and so no further accounting is done. Shouldn't
>>>>>>> unlimited mean that we will never reach the limit? Or am I missing
>>>>>>> something?
>>>>>>>
>>>>>
>>>>> You are missing something, and maybe I should be more clear about that.
>>>>> The static branches can't be disabled (it is only safe to disable them
>>>>> from disarm_static_branches(), when all references are gone). Note that
>>>>> when unlimited, we flip bits, do a transversal, but there is no mention
>>>>> to the static branch.
>>> My little brain still doesn't get this. I wasn't concerned about static
>>> branches. I was worried about memcg_can_account_kmem which will return
>>> false now, doesn't it.
>>>
>>
>> Yes, it will. If I got you right, you are concerned because I said that
>> can't happen. But it will.
>>
>> But I never said that can't happen. I said (ok, I meant) the static
>> branches can't be disabled.
> 
> Ok, then I misunderstood that because the comment was there even before
> static branches were introduced and it made sense to me. This is
> inconsistent with what we do for user accounting because even if we set
> limit to unlimitted we still account. Why should we differ here?
> 
There is another thing as well. Mel was right in his comment: I am
actually abusing this bit (because it is flippable), and it seems the
static branch can be updated more than once...

I'll merge your comments, and fix this.
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