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Message-ID: <20130620023750.GA1194@cerebellum>
Date: Wed, 19 Jun 2013 21:37:50 -0500
From: Seth Jennings <sjenning@...ux.vnet.ibm.com>
To: Bob Liu <lliubbo@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Nitin Gupta <ngupta@...are.org>,
Minchan Kim <minchan@...nel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Dan Magenheimer <dan.magenheimer@...cle.com>,
Robert Jennings <rcj@...ux.vnet.ibm.com>,
Jenifer Hopper <jhopper@...ibm.com>,
Mel Gorman <mgorman@...e.de>,
Johannes Weiner <jweiner@...hat.com>,
Rik van Riel <riel@...hat.com>,
Larry Woodman <lwoodman@...hat.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Dave Hansen <dave@...1.net>, Joe Perches <joe@...ches.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Cody P Schafer <cody@...ux.vnet.ibm.com>,
Hugh Dickens <hughd@...gle.com>,
Paul Mackerras <paulus@...ba.org>,
Linux-MM <linux-mm@...ck.org>,
Linux-Kernel <linux-kernel@...r.kernel.org>,
devel@...verdev.osuosl.org
Subject: Re: [PATCHv13 3/4] zswap: add to mm/
On Mon, Jun 17, 2013 at 02:20:05PM +0800, Bob Liu wrote:
> Hi Seth,
>
> On Tue, Jun 4, 2013 at 4:33 AM, Seth Jennings
> <sjenning@...ux.vnet.ibm.com> wrote:
> > zswap is a thin backend for frontswap that takes pages that are in the process
> > of being swapped out and attempts to compress them and store them in a
> > RAM-based memory pool. This can result in a significant I/O reduction on the
> > swap device and, in the case where decompressing from RAM is faster than
> > reading from the swap device, can also improve workload performance.
> >
> > It also has support for evicting swap pages that are currently compressed in
> > zswap to the swap device on an LRU(ish) basis. This functionality makes zswap a
> > true cache in that, once the cache is full, the oldest pages can be moved out
> > of zswap to the swap device so newer pages can be compressed and stored in
> > zswap.
> >
> > This patch adds the zswap driver to mm/
> >
>
> Do you have any more benchmark can share with me ? To figure out that
> we can benefit from zswap.
>
> I found zswap will cause performance drop when using mmtests-0.10 to test it.
> The config file I'm using is: config-global-dhp__parallelio-memcachetest
>
> The result is:
> (v3.10-rc4-2G-nozswap was without zswap but the performance is better.)
>
> v3.10-rc4 v3.10-rc4
> 2G-zswap-base 2G-nozswap
> Ops memcachetest-0M 604.00 ( 0.00%) 1077.00 ( 78.31%)
> Ops memcachetest-198M 630.00 ( 0.00%) 1007.00 ( 59.84%)
> Ops memcachetest-430M 609.00 ( 0.00%) 939.00 ( 54.19%)
> Ops memcachetest-661M 604.00 ( 0.00%) 845.00 ( 39.90%)
> Ops memcachetest-893M 591.00 ( 0.00%) 839.00 ( 41.96%)
> Ops memcachetest-1125M 599.00 ( 0.00%) 781.00 ( 30.38%)
> Ops memcachetest-1356M 588.00 ( 0.00%) 771.00 ( 31.12%)
> Ops io-duration-0M 0.00 ( 0.00%) 1.00 (-99.00%)
> Ops io-duration-198M 177.00 ( 0.00%) 21.00 ( 88.14%)
> Ops io-duration-430M 168.00 ( 0.00%) 25.00 ( 85.12%)
> Ops io-duration-661M 214.00 ( 0.00%) 30.00 ( 85.98%)
> Ops io-duration-893M 186.00 ( 0.00%) 32.00 ( 82.80%)
> Ops io-duration-1125M 175.00 ( 0.00%) 42.00 ( 76.00%)
> Ops io-duration-1356M 245.00 ( 0.00%) 51.00 ( 79.18%)
> Ops swaptotal-0M 487760.00 ( 0.00%) 459754.00 ( 5.74%)
> Ops swaptotal-198M 563581.00 ( 0.00%) 485194.00 ( 13.91%)
> Ops swaptotal-430M 579472.00 ( 0.00%) 500817.00 ( 13.57%)
> Ops swaptotal-661M 568086.00 ( 0.00%) 524209.00 ( 7.72%)
> Ops swaptotal-893M 584405.00 ( 0.00%) 509846.00 ( 12.76%)
> Ops swaptotal-1125M 572992.00 ( 0.00%) 534115.00 ( 6.78%)
> Ops swaptotal-1356M 573259.00 ( 0.00%) 529814.00 ( 7.58%)
> Ops swapin-0M 231250.00 ( 0.00%) 236069.00 ( -2.08%)
> Ops swapin-198M 312259.00 ( 0.00%) 239149.00 ( 23.41%)
> Ops swapin-430M 327178.00 ( 0.00%) 246803.00 ( 24.57%)
> Ops swapin-661M 319575.00 ( 0.00%) 273644.00 ( 14.37%)
> Ops swapin-893M 328195.00 ( 0.00%) 257327.00 ( 21.59%)
> Ops swapin-1125M 317345.00 ( 0.00%) 271109.00 ( 14.57%)
> Ops swapin-1356M 312858.00 ( 0.00%) 266050.00 ( 14.96%)
> Ops minorfaults-0M 592150.00 ( 0.00%) 646076.00 ( -9.11%)
> Ops minorfaults-198M 637339.00 ( 0.00%) 676441.00 ( -6.14%)
> Ops minorfaults-430M 626228.00 ( 0.00%) 684715.00 ( -9.34%)
> Ops minorfaults-661M 625089.00 ( 0.00%) 670639.00 ( -7.29%)
> Ops minorfaults-893M 612877.00 ( 0.00%) 669723.00 ( -9.28%)
> Ops minorfaults-1125M 624800.00 ( 0.00%) 667025.00 ( -6.76%)
> Ops minorfaults-1356M 618800.00 ( 0.00%) 657600.00 ( -6.27%)
> Ops majorfaults-0M 67664.00 ( 0.00%) 40060.00 ( 40.80%)
> Ops majorfaults-198M 72377.00 ( 0.00%) 39517.00 ( 45.40%)
> Ops majorfaults-430M 71822.00 ( 0.00%) 38895.00 ( 45.85%)
> Ops majorfaults-661M 70009.00 ( 0.00%) 39625.00 ( 43.40%)
> Ops majorfaults-893M 74988.00 ( 0.00%) 38073.00 ( 49.23%)
> Ops majorfaults-1125M 72458.00 ( 0.00%) 38206.00 ( 47.27%)
> Ops majorfaults-1356M 70549.00 ( 0.00%) 37430.00 ( 46.94%)
Just made a mmtests run of my own and got very different results:
parallelio-memcachetest
v3.10-rc6 v3.10-rc6
base zswap
Ops memcachetest-0M 7815.00 ( 0.00%) 7843.00 ( 0.36%)
Ops memcachetest-596M 12116.00 ( 0.00%) 12158.00 ( 0.35%)
Ops memcachetest-1989M 2226.00 ( 0.00%) 5314.00 (138.72%)
Ops memcachetest-3382M 1910.00 ( 0.00%) 4427.00 (131.78%)
Ops io-duration-0M 0.00 ( 0.00%) 0.00 ( 0.00%)
Ops io-duration-596M 18.00 ( 0.00%) 12.00 ( 33.33%)
Ops io-duration-1989M 82.00 ( 0.00%) 57.00 ( 30.49%)
Ops io-duration-3382M 91.00 ( 0.00%) 94.00 ( -3.30%)
Ops swaptotal-0M 0.00 ( 0.00%) 0.00 ( 0.00%)
Ops swaptotal-596M 0.00 ( 0.00%) 0.00 ( 0.00%)
Ops swaptotal-1989M 305182.00 ( 0.00%) 91508.00 ( 70.02%)
Ops swaptotal-3382M 353389.00 ( 0.00%) 74932.00 ( 78.80%)
Ops swapin-0M 0.00 ( 0.00%) 0.00 ( 0.00%)
Ops swapin-596M 0.00 ( 0.00%) 0.00 ( 0.00%)
Ops swapin-1989M 131071.00 ( 0.00%) 45657.00 ( 65.17%)
Ops swapin-3382M 135003.00 ( 0.00%) 37245.00 ( 72.41%)
Ops minorfaults-0M 1201113.00 ( 0.00%) 1201229.00 ( -0.01%)
Ops minorfaults-596M 1218437.00 ( 0.00%) 1218824.00 ( -0.03%)
Ops minorfaults-1989M 1260652.00 ( 0.00%) 1270762.00 ( -0.80%)
Ops minorfaults-3382M 1251389.00 ( 0.00%) 1248756.00 ( 0.21%)
Ops majorfaults-0M 0.00 ( 0.00%) 0.00 ( 0.00%)
Ops majorfaults-596M 34.00 ( 0.00%) 0.00 ( 0.00%)
Ops majorfaults-1989M 16561.00 ( 0.00%) 7789.00 ( 52.97%)
Ops majorfaults-3382M 17031.00 ( 0.00%) 6372.00 ( 62.59%)
Basically the results show that once swapping starts (which happens even in the
0MB case in your results which is puzzling), zswap reduces swapins by around
70% (and as a result swaptotal and majorfaults) and increases memcached
throughput by over 130% compared to the normal swapping case w/o zswap.
This test illustrates a great use case for zswap. The test is really designed
to detect suboptimal page reclaim decisions. Ideally the memcached pages would
never reach the end of the inactive LRU and be swapped out. However, since
there is a lot of I/O going on, if a memcached page does get put on the
inactive list, it can quickly move to the end. In this case, zswap catches the
page and memcached has a chance to fault it back in from the compressed cache
before actual swapping to disk occurs.
Seth
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