linux-kernel - Re: [PATCH 30/35] Skip the PCP list search by counting the order and type of pages on list

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Date:	Mon, 16 Mar 2009 16:51:03 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 30/35] Skip the PCP list search by counting the order
	and type of pages on list

On Mon, Mar 16, 2009 at 12:31:44PM -0400, Christoph Lameter wrote:
> On Mon, 16 Mar 2009, Mel Gorman wrote:
> 
> >
> >  struct per_cpu_pages {
> > -	int count;		/* number of pages in the list */
> > +	/* The total number of pages on the PCP lists */
> > +	int count;
> > +
> > +	/* Count of each migratetype and order */
> > +	u8 mocount[MIGRATE_PCPTYPES][PAGE_ALLOC_COSTLY_ORDER+1];
> 
> What about overflow? You could have more than 255 pages of a given type in
> a pcp.
> 

Are you sure? The maximum size I would expect is pcp->high which is
6 * pcp->batch which is limited in size. I might have missed something
though.

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