linux-kernel - Re: [PATCH 11/20] Inline get_page_from

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Date:	Wed, 25 Feb 2009 01:08:10 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
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>,
	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>
Subject: Re: [PATCH 11/20] Inline get_page_from_freelist() in the fast-path

On Wednesday 25 February 2009 00:32:53 Mel Gorman wrote:
> On Tue, Feb 24, 2009 at 02:32:37AM +1100, Nick Piggin wrote:
> > On Monday 23 February 2009 10:17:20 Mel Gorman wrote:
> > > In the best-case scenario, use an inlined version of
> > > get_page_from_freelist(). This increases the size of the text but
> > > avoids time spent pushing arguments onto the stack.
> >
> > I'm quite fond of inlining ;) But it can increase register pressure as
> > well as icache footprint as well. x86-64 isn't spilling a lot more
> > registers to stack after these changes, is it?
>
> I didn't actually check that closely so I don't know for sure. Is there a
> handier way of figuring it out than eyeballing the assembly? In the end

I guess the 5 second check is to look at how much stack the function
uses. OTOH I think gcc does do a reasonable job at register allocation.


> I dropped the inline of this function anyway. It means the patches
> reduce rather than increase text size which is a bit more clear-cut.

Cool, clear cut patches for round 1 should help to get things moving.


> > In which case you will get extra icache footprint. What speedup does
> > it give in the cache-hot microbenchmark case?
>
> I wasn't measuring with a microbenchmark at the time of writing so I don't
> know. I was going entirely by profile counts running kernbench and the
> time spent running the benchmark.

OK. Well seeing as you have dropped this for the moment, let's not
dwell on it ;)

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