linux-kernel - Re: [patch] vmscan: respect higher order in zone

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Message-ID: <20090218102603.GA2160@cmpxchg.org>
Date:	Wed, 18 Feb 2009 11:26:03 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] vmscan: respect higher order in zone_reclaim()

On Wed, Feb 18, 2009 at 10:12:04AM +0000, Mel Gorman wrote:
> On Tue, Feb 17, 2009 at 08:48:27PM +0100, Johannes Weiner wrote:
> > zone_reclaim() already tries to free the requested 2^order pages but
> > doesn't pass the order information into the inner reclaim code.
> > 
> > This prevents lumpy reclaim from happening on higher orders although
> > the caller explicitely asked for that.
> > 
> > Fix it up by initializing the order field of the scan control
> > according to the request.
> > 
> 
> I'm fine with the patch but the changelog could have been better.  Optionally
> take this changelog but either way.
> 
> Acked-by: Mel Gorman <mel@....ul.ie>
> 
> Optional alternative changelog
> ==============================
> 
> During page allocation, there are two stages of direct reclaim that are applied
> to each zone in the preferred list. The first stage using zone_reclaim()
> reclaims unmapped file backed pages and slab pages if over defined limits as
> these are cheaper to reclaim. The caller specifies the order of the target
> allocation but the scan control is not being correctly initialised.
> 
> The impact is that the correct number of pages are being reclaimed but that
> lumpy reclaim is not being applied. This increases the chances of a full
> direct reclaim via try_to_free_pages() is required.
> 
> This patch initialises the order field of the scan control as requested
> by the caller.

Agreed, this is better.  Thank you, Mel.
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