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

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Date:	Fri, 12 Sep 2008 21:37:52 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, apw@...dowen.org
Subject: Re: [PATCH] Mark the correct zone as full when scanning zonelists

On (12/09/08 10:10), KAMEZAWA Hiroyuki didst pronounce:
> On Thu, 11 Sep 2008 14:41:55 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > 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.
> > 
> Hmm, should we rename
> 
>  next_zone_zonelist() => get_appropriate_zone_from_list()
> 
> or some better name ?
> 

Maybe as a separate patch, but to be honest the name still makes sense
to me but I'm biased.

> > > 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?
> > 
> Maybe yes. But it's better to show where this patch really fixes.
> Is this a fix for misunderstanding usage of zoneref in
> mm/page_alloc.c::get_page_from_freelist() ?
> 
> == here ?==
>   if (NUMA_BUILD)
> 	zlc_mark_zone_full(zonelist, z);
> 

I spelled this out a bit better hopefully in the updated changelog.

Thanks

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