linux-kernel - Re: [patch 3/3][rfc] vmscan: batched swap slot allocation

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Date:	Mon, 20 Apr 2009 23:38:56 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, riel@...hat.com,
	hugh@...itas.com
Subject: Re: [patch 3/3][rfc] vmscan: batched swap slot allocation

On Mon, Apr 20, 2009 at 01:53:03PM -0700, Andrew Morton wrote:
> On Mon, 20 Apr 2009 22:31:19 +0200
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > A test program creates an anonymous memory mapping the size of the
> > system's RAM (2G).  It faults all pages of it linearly, then kicks off
> > 128 reclaimers (on 4 cores) that map, fault and unmap 2G in sum and
> > parallel, thereby evicting the first mapping onto swap.
> > 
> > The time is then taken for the initial mapping to get faulted in from
> > swap linearly again, thus measuring how bad the 128 reclaimers
> > distributed the pages on the swap space.
> > 
> >   Average over 5 runs, standard deviation in parens:
> > 
> >       swap-in          user            system            total
> > 
> > old:  74.97s (0.38s)   0.52s (0.02s)   291.07s (3.28s)   2m52.66s (0m1.32s)
> > new:  45.26s (0.68s)   0.53s (0.01s)   250.47s (5.17s)   2m45.93s (0m2.63s)
> > 
> > where old is current mmotm snapshot 2009-04-17-15-19 and new is these
> > three patches applied to it.
> > 
> > Test program attached.  Kernbench didn't show any differences on my
> > single core x86 laptop with 256mb ram (poor thing).
> 
> qsbench is pretty good at fragmenting swapspace.  It would be vaguely
> interesting to see what effect you've had on its runtime.
> 
> I've found that qsbench's runtimes are fairly chaotic when it's
> operating at the transition point between all-in-core and
> madly-swapping, so a bit of thought and caution is needed.
>
> I used to run it with
> 
> 	./qsbench -p 4 -m 96
> 
> on a 256MB machine and it had sufficiently repeatable runtimes to be
> useful.
> 
> There's a copy of qsbench in
> http://userweb.kernel.org/~akpm/stuff/ext3-tools.tar.gz

Thanks a lot.

> I wonder what effect this patch has upon hibernate/resume performance.

Good point, I will test this.
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