linux-kernel - Re: [PATCH] Mark the correct zone as full when scanning zonelists

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Message-ID: <20080915232056.GA23031@csn.ul.ie>
Date:	Tue, 16 Sep 2008 00:20:57 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, apw@...dowen.org
Subject: Re: [PATCH] Mark the correct zone as full when scanning zonelists

On (11/09/08 14:41), Andrew Morton didst pronounce:
> On Thu, 11 Sep 2008 22:25:51 +0100
> Mel Gorman <mel@....ul.ie> wrote:
> 
> > The for_each_zone_zonelist() uses a struct zoneref *z cursor when scanning
> > zonelists to keep track of where in the zonelist it is. The zoneref that
> > is returned corresponds to the the next zone that is to be scanned, not
> > the current one as it originally thought of as an opaque list.
> > 
> > When the page allocator is scanning a zonelist, it marks zones that it
> > temporarily full zones to eliminate near-future scanning attempts.
> 
> That sentence needs help.
> 
> > It uses
> > the zoneref for the marking and consequently the incorrect zone gets marked
> > full. This leads to a suitable zone being skipped in the mistaken belief
> > it is full. This patch corrects the problem by changing zoneref to be the
> > current zone being scanned instead of the next one.
> 
> Applicable to 2.6.26 as well, yes?
> 
> 
> Someone reported a bug a few weeks ago which I think this patch will fix,
> yes?  I don't remember who that was, nor do I recall the precise details
> of what the userspace-visible (mis)behaviour was.
> 
> Are you able to fill in the gaps here? 

I searched through the archives and couldn't find a bug report that this
patch may be the fix to. However, I understand that the initial leader
could have been a lot better.

> Put yourself in the position of
> a poor little -stable maintainer scratching his head wondering ytf he
> was sent this patch.
> 
> Thanks.
> 

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