linux-kernel - Re: [PATCH v3 19/28] slab: per-memcg accounting of slab caches

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Message-ID: <4FC4F5A8.9060506@parallels.com>
Date:	Tue, 29 May 2012 20:13:28 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<linux-mm@...ck.org>, <kamezawa.hiroyu@...fujitsu.com>,
	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>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v3 19/28] slab: per-memcg accounting of slab caches

On 05/29/2012 08:07 PM, Glauber Costa wrote:
> On 05/29/2012 06:52 PM, Christoph Lameter wrote:
>> On Fri, 25 May 2012, Glauber Costa wrote:
>>
>>> > This patch charges allocation of a slab object to a particular
>>> > memcg.
>> Ok so a requirement is to support tracking of individual slab
>> objects to cgroups? That is going to be quite expensive since it will
>> touch the hotpaths.
>>
>
> No, we track pages. But all the objects in the page belong to the same
> cgroup.
>

Also, please note the following:

The code that relays us to the right cache, is wrapped inside a static 
branch. Whoever is not using more than the root cgroup, will not suffer 
a single bit.

If you are, but your process is in the right cgroup, you will 
unfortunately pay function call penalty(*), but the code will make and 
effort to detect that as early as possible and resume.


(*) Not even then if you fall in the following categories, that are 
resolved inline:

+       if (!current->mm)
+               return cachep;
+       if (in_interrupt())
+               return cachep;
+       if (gfp & __GFP_NOFAIL)
+               return cachep;

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