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

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Message-ID: <20090316122806.GE30802@wotan.suse.de>
Date:	Mon, 16 Mar 2009 13:28:06 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Mel Gorman <mel@....ul.ie>
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 12:11:22PM +0000, Mel Gorman wrote:
> On Mon, Mar 16, 2009 at 12:45:55PM +0100, Nick Piggin wrote:
> > On Mon, Mar 16, 2009 at 09:45:55AM +0000, Mel Gorman wrote:
> > > Here is V3 of an attempt to cleanup and optimise the page allocator and should
> > > be ready for general testing. The page allocator is now faster (16%
> > > reduced time overall for kernbench on one machine) and it has a smaller cache
> > > footprint (16.5% less L1 cache misses and 19.5% less L2 cache misses for
> > > kernbench on one machine). The text footprint has unfortunately increased,
> > > largely due to the introduction of a form of lazy buddy merging mechanism
> > > that avoids cache misses by postponing buddy merging until a high-order
> > > allocation needs it.
> > 
> > BTW. I would feel better about this if it gets merged in stages, with
> > functional changes split out, and also code optimisations and omore
> > obvious performace improvements split out and preferably merged first.
> > 
> 
> The ordering of the patches was such that least-controversial stuff is
> at the start of the patchset. The intention was to be able to select a
> cut-off point and say "that's enough for now"
> 
> > At a very quick glance, the first 25 or so patches should go in first,
> > and that gives a much better base to compare subsequent functional
> > changes with.
> 
> That's reasonable. I've requeued tests for the patchset up to 25 to see what
> that looks like. There is also a part of a later patch that reduces how much
> time is spent with interrupts disabled. I should split that out and move it
> back to within the cut-off point as something that is "obviously good".

OK cool. It also means we can start getting benefit of some of them
sooner. I hope most of the obvious ones can be merged in 2.6.30.

 
> > Patch 18 for example is really significant, and should
> > almost be 2.6.29/-stable material IMO.
> > 
> 
> My impression was that -stable was only for functional regressions where
> as this is really a performance thing.

A performance regression like this in the core page allocator is a
pretty important problem. The fix is obvious. But maybe you're right.
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