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

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Message-ID: <20090223114221.GD6740@csn.ul.ie>
Date:	Mon, 23 Feb 2009 11:42:21 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	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 Mon, Feb 23, 2009 at 09:21:09AM +0200, Pekka Enberg wrote:
> On Mon, Feb 23, 2009 at 1:17 AM, Mel Gorman <mel@....ul.ie> 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.
> >
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> 
> It's not obvious to me why this would be a huge win so I suppose this
> patch description could use numbers.

I don't have the exact numbers from the profiles any more but the
function entry and exit was about 1/20th of the cost of the path when
zeroing pages is not taken into account.

> Note: we used to do tricks like
> these in slab.c but got rid of most of them to reduce kernel text size
> which is probably why the patch seems bit backwards to me.
> 

I'll be rechecking this patch in particular because it's likely the
biggest text bloat in the entire series.

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