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Subject: Re: [PATCH 07/20] Simplify the check on whether cpusets are a
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From: Peter Zijlstra <peterz@infradead.org>
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Date: Mon, 23 Feb 2009 10:07:52 +0100
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To: Pekka J Enberg <penberg@cs.helsinki.fi>
Cc: Mel Gorman <mel@csn.ul.ie>, Linux Memory Management List <linux-mm@kvack.org>, Rik van Riel <riel@redhat.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Nick Piggin <npiggin@suse.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Lin Ming <ming.m.lin@intel.com>, Zhang Yanmin <yanmin_zhang@linux.intel.com>
List-ID: <linux-mm.kvack.org>

On Mon, 2009-02-23 at 09:14 +0200, Pekka J Enberg wrote:
> On Sun, 22 Feb 2009, Mel Gorman wrote:
> > The check whether cpuset contraints need to be checked or not is complex
> > and often repeated.  This patch makes the check in advance to the comparison
> > is simplier to compute.
> > 
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> 
> You can do that in a cleaner way by defining ALLOC_CPUSET to be zero when 
> CONFIG_CPUSETS is disabled. Something like following untested patch:
> 
> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
> ---
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5675b30..18b687d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1135,7 +1135,12 @@ failed:
>  #define ALLOC_WMARK_HIGH	0x08 /* use pages_high watermark */
>  #define ALLOC_HARDER		0x10 /* try to alloc harder */
>  #define ALLOC_HIGH		0x20 /* __GFP_HIGH set */
> +
> +#ifdef CONFIG_CPUSETS
>  #define ALLOC_CPUSET		0x40 /* check for correct cpuset */
> +#else
> +#define ALLOC_CPUSET		0x00
> +#endif
>  

Mel's patch however even avoids the code when cpusets are configured but
not actively used (the most common case for distro kernels).

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