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

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Date:	Fri, 12 Sep 2008 10:10:07 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>, 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 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 ?

> > 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);

Thanks,
-Kame

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