linux-kernel - Re: [PATCH 3/3] page-allocator: Move pcp static fields for high and batch off-pcp and onto the zone

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Message-ID: <20090818205050.GA756@csn.ul.ie>
Date:	Tue, 18 Aug 2009 21:50:50 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] page-allocator: Move pcp static fields for high
	and batch off-pcp and onto the zone

On Tue, Aug 18, 2009 at 01:56:22PM -0400, Christoph Lameter wrote:
> On Tue, 18 Aug 2009, Mel Gorman wrote:
> 
> > On Tue, Aug 18, 2009 at 10:18:48AM -0400, Christoph Lameter wrote:
> > >
> > > This will increase the cache footprint for the hot code path. Could these
> > > new variable be moved next to zone fields that are already in use there?
> > > The pageset array is used f.e.
> > >
> >
> > pageset is ____cacheline_aligned_in_smp so putting pcp->high/batch near
> > it won't help in terms of cache footprint. This is why I located it near
> > watermarks because it's known they'll be needed at roughly the same time
> > pcp->high/batch would be normally accessed.
> 
> watermarks are not accessed from the hot code path in free_hot_cold page.
> 

They are used in a commonly-used path for allocation so there is some
advantage. Put beside pageset, there is no advantage as that structure
is already aligned to a cache-line.

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