linux-kernel - Re: [PATCH 07/20] Simplify the check on whether cpusets are a factor or not

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Date:	Mon, 23 Feb 2009 10:07:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Pekka J Enberg <penberg@...helsinki.fi>
Cc:	Mel Gorman <mel@....ul.ie>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH 07/20] Simplify the check on whether cpusets are a
 factor or not

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@....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@...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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