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Date: Thu, 27 Sep 2012 14:34:35 +0100
From: Mel Gorman <mgorman@suse.de>
To: Glauber Costa <glommer@parallels.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        kamezawa.hiroyu@jp.fujitsu.com, devel@openvz.org,
        Tejun Heo <tj@kernel.org>, linux-mm@kvack.org,
        Suleiman Souhlal <suleiman@google.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        David Rientjes <rientjes@google.com>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@cs.helsinki.fi>, Michal Hocko <mhocko@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>, Rik van Riel <riel@redhat.com>,
        Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag
Message-ID: <20120927133435.GE3429@suse.de>
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On Tue, Sep 18, 2012 at 06:04:02PM +0400, Glauber Costa wrote:
> This flag is used to indicate to the callees that this allocation is a
> kernel allocation in process context, and should be accounted to
> current's memcg. It takes numerical place of the of the recently removed
> __GFP_NO_KSWAPD.
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> CC: Rik van Riel <riel@redhat.com>
> CC: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

I agree with Christophs recommendation that this flag always exist instead
of being 0 in the !MEMCG_KMEM case. If __GFP_KMEMCG ever is used in another
part of the VM (which would be unexpected but still) then the behaviour
might differ too much between MEMCG_KMEM and !MEMCG_KMEM cases. As unlikely
as the case is, it's not impossible.

For tracing __GFP_KMEMCG should have an entry in
include/trace/events/gfpflags.h

Get rid of the CONFIG_MEMCG_KMEM check and update
include/trace/events/gfpflags.h and then feel free to stick my Acked-by
on it.

-- 
Mel Gorman
SUSE Labs