linux-kernel - Re: [PATCH 00/35] Cleanup and optimise the page allocator V3

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Message-ID: <20090318150724.GB4629@csn.ul.ie>
Date:	Wed, 18 Mar 2009 15:07:24 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	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>
Subject: Re: [PATCH 00/35] Cleanup and optimise the page allocator V3

On Mon, Mar 16, 2009 at 06:05:51PM +0100, Nick Piggin wrote:
> On Mon, Mar 16, 2009 at 04:56:28PM +0000, Mel Gorman wrote:
> > On Mon, Mar 16, 2009 at 04:53:42PM +0100, Nick Piggin wrote:
> > > So yes definitely I think there should be a very real impact on
> > > higher order coalescing no matter what you do.
> > > 
> > 
> > Because this is not straight-forward at all, I'll put lazy buddy onto
> > the back-burner and exhaust all other possibilities before revisiting it
> > again.
> 
> If it is such a big improvement, I expect *most* people will want
> it and we probably should do it.

I'll be reinvestigating it in isolation. It's possible that high-order and
compound pages on the PCP lists is enough of a delayed buddy merging that
the benefit from lazy buddy is marginal.

> But just that it will not play
> nicely with fragmentation and so you'd need to look into it and
> devise some way those users can tune it to be nicer.
> 

Which is why I'm going to postpone it for now.

> > > unmovable zone fragmentation is more important point because it
> > > eventually can destroy the movable zone.
> > > 
> > 
> > Which is why rmqueue_fallback() also merges up all buddies before making
> > any decisions but I accept your points.
> 
> Right, that merge of buddies will only be able to look at what is
> currently free. Wheras non-lazy buddy can pull out higher orders
> before reallocating them.
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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