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

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Date:	Wed, 16 May 2012 10:19:15 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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

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.


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