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Subject: Re: [PATCH 08/25] Calculate the preferred zone for allocation only
 once
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Mel Gorman <mel@csn.ul.ie>
Cc: Linux Memory Management List <linux-mm@kvack.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
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       Lin Ming <ming.m.lin@intel.com>,
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       Andrew Morton <akpm@linux-foundation.org>
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Date: Tue, 21 Apr 2009 11:29:16 +0300
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On Tue, 2009-04-21 at 09:27 +0100, Mel Gorman wrote:
> > You might want to add an explanation to the changelog why this change is
> > safe. It looked like a functional change at first glance and it was
> > pretty difficult to convince myself that __alloc_pages_slowpath() will
> > always return NULL when there's no preferred zone because of the other
> > cleanups in this patch series.
> > 
> 
> Is this better?
> 
> get_page_from_freelist() can be called multiple times for an allocation.
> Part of this calculates the preferred_zone which is the first usable zone in
> the zonelist but the zone depends on the GFP flags specified at the beginning
> of the allocation call. This patch calculates preferred_zone once. It's safe
> to do this because if preferred_zone is NULL at the start of the call, no
> amount of direct reclaim or other actions will change the fact the allocation
> will fail.

Perfect!