linux-kernel - Re: [PATCH 08/25] Calculate the preferred zone for allocation only once

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Message-Id: <1240302556.771.65.camel@penberg-laptop>
Date:	Tue, 21 Apr 2009 11:29:16 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 08/25] Calculate the preferred zone for allocation only
 once

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!

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