linux-kernel - Re: [PATCH 20/35] Use a pre-calculated value for num_online

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Date:	Mon, 16 Mar 2009 12:46:44 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Mel Gorman <mel@....ul.ie>,
	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>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	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 20/35] Use a pre-calculated value for num_online_nodes()

On Mon, Mar 16, 2009 at 10:42:34PM +1100, Nick Piggin wrote:
> On Monday 16 March 2009 20:46:15 Mel Gorman wrote:
> > num_online_nodes() is called by the page allocator to decide whether the
> > zonelist needs to be filtered based on cpusets or the zonelist cache.
> > This is actually a heavy function and touches a number of cache lines.
> > This patch stores the number of online nodes at boot time and when
> > nodes get onlined and offlined.
> >
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > ---
> >  include/linux/nodemask.h |   16 ++++++++++++++--
> >  mm/page_alloc.c          |    6 ++++--
> >  2 files changed, 18 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
> > index 848025c..4749e30 100644
> > --- a/include/linux/nodemask.h
> > +++ b/include/linux/nodemask.h
> > @@ -449,13 +449,25 @@ static inline int num_node_state(enum node_states
> > state) node;					\
> >  })
> >
> > +/* Recorded value for num_online_nodes() */
> > +extern int static_num_online_nodes;
> 
> __read_mostly, please. Check this for any other place you've added
> global cachelines that are referenced by the allocator.

OK I'm blind, sorry ignore that :P
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