linux-kernel - Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code regions

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Date:	Wed, 16 May 2012 16:55:49 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizefan@...wei.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, devel@...nvz.org,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code
 regions

(2012/05/16 15:19), Glauber Costa wrote:

> On 05/15/2012 06:46 AM, KAMEZAWA Hiroyuki wrote:
>> (2012/05/12 2:44), Glauber Costa wrote:
>>
>>> This patch creates a mechanism that skip memcg allocations during
>>> certain pieces of our core code. It basically works in the same way
>>> as preempt_disable()/preempt_enable(): By marking a region under
>>> which all allocations will be accounted to the root memcg.
>>>
>>> We need this to prevent races in early cache creation, when we
>>> allocate data using caches that are not necessarily created already.
>>>
>>> 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>
>>
>>
>> The concept seems okay to me but...
>>
>>> ---
>>>   include/linux/sched.h |    1 +
>>>   mm/memcontrol.c       |   25 +++++++++++++++++++++++++
>>>   2 files changed, 26 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>> index 81a173c..0501114 100644
>>> --- a/include/linux/sched.h
>>> +++ b/include/linux/sched.h
>>> @@ -1613,6 +1613,7 @@ struct task_struct {
>>>   		unsigned long nr_pages;	/* uncharged usage */
>>>   		unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
>>>   	} memcg_batch;
>>> +	atomic_t memcg_kmem_skip_account;
>>
>>
>> If only 'current' thread touch this, you don't need to make this atomic counter.
>> you can use 'long'.
>>
> You're absolutely right, Kame, thanks.
> I first used atomic_t because I had it tested against current->mm->owner.
> 
> Do you, btw, agree to use current instead of owner here?
> You can find the rationale in earlier mails between me and Suleiman.

I agree to use current. This information depends on the context of callers.

Thanks,
-Kame


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