linux-kernel - Re: [PATCH 00/25] Cleanup and optimise the page allocator V5

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Date:	Fri, 20 Mar 2009 16:27:16 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/25] Cleanup and optimise the page allocator V5

On Fri, Mar 20, 2009 at 12:07:22PM -0400, Christoph Lameter wrote:
> On Fri, 20 Mar 2009, Mel Gorman wrote:
> 
> > good idea one way or the other. Course, this meant a search of the PCP
> > lists or increasing the size of the PCP structure - swings and
> > roundabouts :/
> 
> The PCP list structure irks me a bit. Manipulating doubly linked lists
> means touching at least 3 cachelines.

Yeah, and bloats the structure quite a bit. It's what hits the
one-list-per-migratetype the hardest.

> Is it possible to go to a simple
> linked list (one cacheline to be touched)?

I considered it but it breaks the hot/cold allocation/freeing logic and
the search code became weird enough looking fast enough that I dropped
it.

> Or an array of pointers to
> pages instead (one cacheline may contian multiple pointers to pcp pages
> which means multiple pages could be handled with a single cacheline)?
> 

An array of pointers is promising but it would bloat the structure quiet a
bit too.

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