linux-kernel - Re: [PATCH 16/23] slab: provide kmalloc_no

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Date:	Thu, 26 Apr 2012 09:13:51 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	cgroups@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...nvz.org,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, fweisbec@...il.com,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 16/23] slab: provide kmalloc_no_account

(2012/04/25 23:29), Glauber Costa wrote:

> On 04/24/2012 10:44 PM, KAMEZAWA Hiroyuki wrote:
>> (2012/04/23 8:53), Glauber Costa wrote:
>>
>>> Some allocations need to be accounted to the root memcg regardless
>>> of their context. One trivial example, is the allocations we do
>>> during the memcg slab cache creation themselves. Strictly speaking,
>>> they could go to the parent, but it is way easier to bill them to
>>> the root cgroup.
>>>
>>> Only generic kmalloc allocations are allowed to be bypassed.
>>>
>>> The function is not exported, because drivers code should always
>>> be accounted.
>>>
>>> This code is mosly written by Suleiman Souhlal.
>>>
>>> Signed-off-by: Glauber Costa<glommer@...allels.com>
>>> CC: Christoph Lameter<cl@...ux.com>
>>> CC: Pekka Enberg<penberg@...helsinki.fi>
>>> CC: Michal Hocko<mhocko@...e.cz>
>>> CC: Kamezawa Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
>>> CC: Johannes Weiner<hannes@...xchg.org>
>>> CC: Suleiman Souhlal<suleiman@...gle.com>
>>
>>
>> Seems reasonable.
>> Reviewed-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
>>
>> Hmm...but can't we find the 'context' in automatic way ?
>>
> 
> Not that I can think of. Well, actually, not without adding some tests
> to the allocation path I'd rather not (like testing for the return
> address and then doing a table lookup, etc)
> 
> An option would be to store it in the task_struct. So we would allocate
> as following:
> 
> memcg_skip_account_start(p);
> do_a_bunch_of_allocations();
> memcg_skip_account_stop(p);
> 
> The problem with that, is that it is quite easy to abuse.
> but if we don't export that to modules, it would be acceptable.
> 
> Question is, given the fact that the number of kmalloc_no_account() is
> expected to be really small, is it worth it?
> 

ok, but.... There was an idea __GFP_NOACCOUNT, which is better ?
Are you afraid that__GFP_NOACCOUNT can be spread too much rather than kmalloc_no_account() ?


Thanks,
-Kame


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