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

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Message-ID: <00000139dedaeb71-1199f5a3-c122-460e-a1d8-74174a9d96db-000000@email.amazonses.com>
Date:	Wed, 19 Sep 2012 14:07:33 +0000
From:	Christoph Lameter <cl@...ux.com>
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>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.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 Wed, 19 Sep 2012, Glauber Costa wrote:

> On 09/18/2012 07:06 PM, Christoph Lameter wrote:
> > On Tue, 18 Sep 2012, Glauber Costa wrote:
> >
> >> +++ b/include/linux/gfp.h
> >> @@ -35,6 +35,11 @@ struct vm_area_struct;
> >>  #else
> >>  #define ___GFP_NOTRACK		0
> >>  #endif
> >> +#ifdef CONFIG_MEMCG_KMEM
> >> +#define ___GFP_KMEMCG		0x400000u
> >> +#else
> >> +#define ___GFP_KMEMCG		0
> >> +#endif
> >
> > Could you leave __GFP_MEMCG a simple definition and then define GFP_MEMCG
> > to be zer0 if !MEMCG_KMEM? I think that would be cleaner and the
> > __GFP_KMEMCHECK another case that would be good to fix up.
> >
> >
> >
> I can, but what does this buy us?

All the numeric values should be defined with __ unconditionally so that
they can be used in future context. Note the comment above the __GFP_XX
which says "Do not use this directly".

> Also, in any case, this can be done incrementally, and for the other
> flag as well, as you describe.

There is only one other flag that does not follow the scheme. I'd
appreciate it if you could submit a patch to fix up the __GFP_NOTRACK
conditional there.

There is no need to do this incrementally. Do it the right way
immediately.

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