linux-kernel - Re: [PATCH v3 05/13] Add a __GFP

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Date:	Thu, 27 Sep 2012 14:34:35 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, devel@...nvz.org,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
	Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH v3 05/13] Add a __GFP_KMEMCG flag

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@...allels.com>
> CC: Christoph Lameter <cl@...ux.com>
> CC: Pekka Enberg <penberg@...helsinki.fi>
> CC: Michal Hocko <mhocko@...e.cz>
> CC: Johannes Weiner <hannes@...xchg.org>
> CC: Suleiman Souhlal <suleiman@...gle.com>
> CC: Rik van Riel <riel@...hat.com>
> CC: Mel Gorman <mel@....ul.ie>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@...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
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