linux-kernel - Re: [PATCH 17/23] kmem controller charge/uncharge infrastructure

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Date:	Tue, 24 Apr 2012 18:36:02 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	<cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <devel@...nvz.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	"Christoph Lameter" <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 17/23] kmem controller charge/uncharge infrastructure

On 04/24/2012 05:25 PM, David Rientjes wrote:
> On Tue, 24 Apr 2012, Glauber Costa wrote:
>
>> I think memcg is not necessarily wrong. That is because threads in a process
>> share an address space, and you will eventually need to map a page to deliver
>> it to userspace. The mm struct points you to the owner of that.
>>
>> But that is not necessarily true for things that live in the kernel address
>> space.
>>
>> Do you view this differently ?
>>
>
> Yes, for user memory, I see charging to p->mm->owner as allowing that
> process to eventually move and be charged to a different memcg and there's
> no way to do proper accounting if the charge is split amongst different
> memcgs because of thread membership to a set of memcgs.  This is
> consistent with charges for shared memory being moved when a thread
> mapping it moves to a new memcg, as well.

But that's the problem.

When we are dealing with kernel memory, we are allocating a whole slab 
page. It is essentially impossible to track, given a page, which task 
allocated which object.
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