linux-kernel - Re: [PATCH 11/25] Calculate the cold parameter for allocation only once

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Message-ID: <20090421100818.GO12713@csn.ul.ie>
Date:	Tue, 21 Apr 2009 11:08:20 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.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>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 11/25] Calculate the cold parameter for allocation only
	once

On Tue, Apr 21, 2009 at 06:07:24PM +0900, KOSAKI Motohiro wrote:
> > GFP mask is checked for __GFP_COLD has been specified when deciding which
> > end of the PCP lists to use. However, it is happening multiple times per
> > allocation, at least once per zone traversed. Calculate it once.
> > 
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > ---
> >  mm/page_alloc.c |   35 ++++++++++++++++++-----------------
> >  1 files changed, 18 insertions(+), 17 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 1506cd5..51e1ded 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1066,11 +1066,10 @@ void split_page(struct page *page, unsigned int order)
> >   */
> >  static struct page *buffered_rmqueue(struct zone *preferred_zone,
> >  			struct zone *zone, int order, gfp_t gfp_flags,
> > -			int migratetype)
> > +			int migratetype, int cold)
> >  {
> >  	unsigned long flags;
> >  	struct page *page;
> > -	int cold = !!(gfp_flags & __GFP_COLD);
> >  	int cpu;
> 
> Honestly, I don't like this ;-)
> 
> It seems benefit is too small. It don't win against code ugliness, I think.
> 

Ok, I'll drop it for now and then generate figures for it at a later
time. The intention is to have this first set relatively
uncontroversial.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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