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

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Message-Id: <1235380403.6216.16.camel@penberg-laptop>
Date:	Mon, 23 Feb 2009 11:13:23 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Peter Zijlstra <peterz@...radead.org>
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 10:07 +0100, Peter Zijlstra wrote:
> 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).

Right. Combining both patches is probably the best solution then as we
get rid of the #ifdef in get_page_from_freelist().

			Pekka

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