linux-kernel - Re: [PATCH 04/10] memcg: skip memcg kmem allocations in specified code regions

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Message-ID: <50169593.5020506@parallels.com>
Date:	Mon, 30 Jul 2012 18:09:23 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Greg Thelen <gthelen@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>, <devel@...nvz.org>,
	<cgroups@...r.kernel.org>, Pekka Enberg <penberg@...helsinki.fi>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH 04/10] memcg: skip memcg kmem allocations in specified
 code regions

On 07/30/2012 04:50 PM, Kirill A. Shutemov wrote:
> On Wed, Jul 25, 2012 at 06:38:15PM +0400, 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.
> 
> Why not a GFP_* flag?
> 

The main reason for this is to prevent nested calls of
kmem_cache_create(), since they could create (and in my tests, do
create) funny circular dependencies with each other. So the cache
creation itself would proceed without involving memcg.

At first, it is a bit weird to have cache creation itself depending on a
allocation flag test.
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