linux-kernel - Re: [RFC PATCH] mm: handle simple case in free_pcppages

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Message-ID: <20110210140543.GJ17873@csn.ul.ie>
Date:	Thu, 10 Feb 2011 14:05:43 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Namhyung Kim <namhyung@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: handle simple case in free_pcppages_bulk()

On Thu, Feb 10, 2011 at 10:38:59PM +0900, Minchan Kim wrote:
> On Thu, Feb 10, 2011 at 10:18 PM, Namhyung Kim <namhyung@...il.com> wrote:
> > 2011-02-10 (???), 22:10 +0900, Minchan Kim:
> >> Hello Namhyung,
> >>
> >
> > Hi Minchan,
> >
> >
> >> On Thu, Feb 10, 2011 at 8:46 PM, Namhyung Kim <namhyung@...il.com> wrote:
> >> > Now I'm seeing that there are some cases to free all pages in a
> >> > pcp lists. In that case, just frees all pages in the lists instead
> >> > of being bothered with round-robin lists traversal.
> >>
> >> I though about that but I didn't send the patch.
> >> That's because many cases which calls free_pcppages_bulk(,
> >> pcp->count,..) are slow path so it adds comparison overhead on fast
> >> path while it loses the effectiveness in slow path.
> >>
> >
> > Hmm.. How about adding unlikely() then? Doesn't it help much here?
> 
> Yes. It would help but I am not sure how much it is.
> AFAIR, when Mel submit the patch, he tried to prove the effectiveness
> with some experiment and profiler.

Yep. Principally I *think* used netperf running UDP_STREAM for different
buffer sizes and compared oprofile output but I also ran a battery of
benchmarks to check for any other unexpected regression without profiling.

-- 
Mel Gorman
SUSE Labs
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