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Date: Thu, 18 Oct 2012 13:44:57 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Glauber Costa <glommer@parallels.com>
Cc: <linux-mm@kvack.org>, <cgroups@vger.kernel.org>,
        Mel Gorman <mgorman@suse.de>, Tejun Heo <tj@kernel.org>,
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        <linux-kernel@vger.kernel.org>, Pekka Enberg <penberg@cs.helsinki.fi>,
        Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg
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On Thu, 18 Oct 2012 13:24:47 +0400
Glauber Costa <glommer@parallels.com> wrote:

> On 10/18/2012 02:12 AM, Andrew Morton wrote:
> > On Tue, 16 Oct 2012 14:16:44 +0400
> > Glauber Costa <glommer@parallels.com> wrote:
> > 
> >> When a process tries to allocate a page with the __GFP_KMEMCG flag, the
> >> page allocator will call the corresponding memcg functions to validate
> >> the allocation. Tasks in the root memcg can always proceed.
> >>
> >> To avoid adding markers to the page - and a kmem flag that would
> >> necessarily follow, as much as doing page_cgroup lookups for no reason,
> >> whoever is marking its allocations with __GFP_KMEMCG flag is responsible
> >> for telling the page allocator that this is such an allocation at
> >> free_pages() time.
> > 
> > Well, why?  Was that the correct decision?
> > 
> 
> I don't fully understand your question. Is this the same question you
> posed in patch 0, about marking some versus marking all? If so, I
> believe I should have answered it there.

Yes, it's the same question.  The one which has not yet been fully answered ;)