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

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Date:	Thu, 11 Sep 2008 14:41:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
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 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?  Put yourself in the position of
a poor little -stable maintainer scratching his head wondering ytf he
was sent this patch.

Thanks.
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