linux-kernel - Re: [RFC][PATCH] mm: the page of MIGRATE

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Message-ID: <20081107104242.GC13786@csn.ul.ie>
Date:	Fri, 7 Nov 2008 10:42:42 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] mm: the page of MIGRATE_RESERVE don't insert into pcp

On Fri, Nov 07, 2008 at 10:42:24AM +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 6 Nov 2008 16:46:45 +0000
> Mel Gorman <mel@....ul.ie> wrote:
> > > otherwise, the system have unnecessary memory starvation risk
> > > because other cpu can't use this emergency pages.
> > > 
> > > 
> > > 
> > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > > CC: Mel Gorman <mel@....ul.ie>
> > > CC: Christoph Lameter <cl@...ux-foundation.org>
> > > 
> > 
> > This patch seems functionally sound but as Christoph points out, this
> > adds another branch to the fast path. Now, I ran some tests and those that
> > completed didn't show any problems but adding branches in the fast path can
> > eventually lead to hard-to-detect performance problems.
> > 
> dividing pcp-list into MIGRATE_TYPES is bad ?

I do not understand what your question is.

> If divided, we can get rid of scan. 
> 

I don't know what you are saying here either. I think you are saying
that we should avoid scanning the PCP lists for migrate types at all.
That hurts anti-fragmentation as pages can be badly placed if any pcp
page is used.

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