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Message-ID: <Yg8ec9MLblOkHTY9@ziqianlu-nuc9qn>
Date: Fri, 18 Feb 2022 12:20:03 +0800
From: Aaron Lu <aaron.lu@...el.com>
To: Mel Gorman <mgorman@...hsingularity.net>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Vlastimil Babka <vbabka@...e.cz>,
Michal Hocko <mhocko@...nel.org>,
Jesper Dangaard Brouer <brouer@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 5/6] mm/page_alloc: Free pages in a single pass during
bulk free
On Thu, Feb 17, 2022 at 09:31:13AM +0000, Mel Gorman wrote:
> On Thu, Feb 17, 2022 at 09:53:08AM +0800, Aaron Lu wrote:
> > > 2-socket CascadeLake (40 cores, 80 CPUs HT enabled)
> > > 5.17.0-rc3 5.17.0-rc3
> > > vanilla mm-highpcpopt-v2
> > > Hmean page_fault1-processes-2 2694662.26 ( 0.00%) 2695780.35 ( 0.04%)
> > > Hmean page_fault1-processes-5 6425819.34 ( 0.00%) 6435544.57 * 0.15%*
> > > Hmean page_fault1-processes-8 9642169.10 ( 0.00%) 9658962.39 ( 0.17%)
> > > Hmean page_fault1-processes-12 12167502.10 ( 0.00%) 12190163.79 ( 0.19%)
> > > Hmean page_fault1-processes-21 15636859.03 ( 0.00%) 15612447.26 ( -0.16%)
> > > Hmean page_fault1-processes-30 25157348.61 ( 0.00%) 25169456.65 ( 0.05%)
> > > Hmean page_fault1-processes-48 27694013.85 ( 0.00%) 27671111.46 ( -0.08%)
> > > Hmean page_fault1-processes-79 25928742.64 ( 0.00%) 25934202.02 ( 0.02%) <--
> > > Hmean page_fault1-processes-110 25730869.75 ( 0.00%) 25671880.65 * -0.23%*
> > > Hmean page_fault1-processes-141 25626992.42 ( 0.00%) 25629551.61 ( 0.01%)
> > > Hmean page_fault1-processes-172 25611651.35 ( 0.00%) 25614927.99 ( 0.01%)
> > > Hmean page_fault1-processes-203 25577298.75 ( 0.00%) 25583445.59 ( 0.02%)
> > > Hmean page_fault1-processes-234 25580686.07 ( 0.00%) 25608240.71 ( 0.11%)
> > > Hmean page_fault1-processes-265 25570215.47 ( 0.00%) 25568647.58 ( -0.01%)
> > > Hmean page_fault1-processes-296 25549488.62 ( 0.00%) 25543935.00 ( -0.02%)
> > > Hmean page_fault1-processes-320 25555149.05 ( 0.00%) 25575696.74 ( 0.08%)
> > >
> > > The differences are mostly within the noise and the difference close to
> > > $nr_cpus is negligible.
> >
> > I have queued will-it-scale/page_fault1/processes/$nr_cpu on 2 4-sockets
> > servers: CascadeLake and CooperLaker and will let you know the result
> > once it's out.
> >
>
> Thanks, 4 sockets and a later generation would be nice to cover.
>
> > I'm using 'https://github.com/hnaz/linux-mm master' and doing the
> > comparison with commit c000d687ce22("mm/page_alloc: simplify how many
> > pages are selected per pcp list during bulk free") and commit 8391e0a7e172
> > ("mm/page_alloc: free pages in a single pass during bulk free") there.
> >
>
> The baseline looks fine. It's different to what I used but the page_alloc
> shouldn't have much impact.
>
> When looking at will-it-scale, please pay attention to lower CPU counts
> as well and take account changes in standard deviation. Looking at the
I'll also test nr_task=4/16/64 on the 4sockets CooperLake(nr_cpu=144) then.
> old commit (which I acked so I've no excuse), I think it's important to
> look at cases other than the fully utilised case because it's the best
> case for something like will-it-scale pf but it's also an unlikely case
> (all CPUs all faulting continuously).
I see.
>
> I expect there will be different good/bad points based on looking at
> Zen1 results (8 nodes, varying distances, 64 cores with 128 CPUs HT
> enabled)
>
> 5.17.0-rc3 5.17.0-rc3 5.17.0-rc3
> vanilla mm-reverthighpcp-v1 mm-highpcpopt-v2
> Hmean page_fault1-threads-2 2985366.46 ( 0.00%) 2984649.41 ( -0.02%) 3028407.35 ( 1.44%)
> Hmean page_fault1-threads-5 3491833.63 ( 0.00%) 3500237.35 ( 0.24%) 3489971.99 ( -0.05%)
> Hmean page_fault1-threads-8 3254335.58 ( 0.00%) 3277515.51 * 0.71%* 3234275.28 * -0.62%*
> Hmean page_fault1-threads-12 5101504.72 ( 0.00%) 5390649.46 * 5.67%* 5162047.68 ( 1.19%)
> Hmean page_fault1-threads-21 7714265.64 ( 0.00%) 7714763.10 ( 0.01%) 7854367.65 * 1.82%*
> Hmean page_fault1-threads-30 10034561.94 ( 0.00%) 9865446.68 ( -1.69%) 9746368.76 * -2.87%*
> Hmean page_fault1-threads-48 12571351.99 ( 0.00%) 13257508.23 * 5.46%* 12160897.07 * -3.27%*
> Hmean page_fault1-threads-79 11124387.46 ( 0.00%) 10641145.82 * -4.34%* 10677656.39 * -4.02%*
> Hmean page_fault1-threads-110 11980424.12 ( 0.00%) 10778220.84 * -10.03%* 10354249.62 * -13.57%* <-- close to nr_cpus
> Hmean page_fault1-threads-141 9727528.73 ( 0.00%) 9966965.70 ( 2.46%) 9656148.13 ( -0.73%) <-- close to nr_cpus
I have never tested thread mode, because I think the heavy loaded
thread mode is more about testing the mmap_sem contention than page
allocator's performance? It's surprising this patch caused a
performance change.
> Hmean page_fault1-threads-172 11807964.92 ( 0.00%) 10335576.64 * -12.47%* 10443310.45 * -11.56%*
> Hmean page_fault1-threads-203 9471961.29 ( 0.00%) 9749857.24 * 2.93%* 11890019.87 * 25.53%*
> Hmean page_fault1-threads-234 11322381.78 ( 0.00%) 9163162.66 ( -19.07%) 9141561.16 ( -19.26%)
> Hmean page_fault1-threads-265 7956982.52 ( 0.00%) 7774650.20 ( -2.29%) 8292405.57 * 4.22%*
> Hmean page_fault1-threads-296 7892153.88 ( 0.00%) 8272671.84 * 4.82%* 7907026.20 ( 0.19%)
> Hmean page_fault1-threads-327 7957124.50 ( 0.00%) 8078297.34 ( 1.52%) 8129776.79 ( 2.17%)
> Hmean page_fault1-threads-358 7847563.90 ( 0.00%) 8202303.36 ( 4.52%) 8139027.38 ( 3.71%)
> Hmean page_fault1-threads-389 7928386.47 ( 0.00%) 8104732.41 ( 2.22%) 8022002.73 ( 1.18%)
> Hmean page_fault1-threads-420 7690107.89 ( 0.00%) 7587821.54 ( -1.33%) 7783777.95 ( 1.22%)
> Hmean page_fault1-threads-451 7683132.29 ( 0.00%) 7979578.21 ( 3.86%) 7693067.13 ( 0.13%)
> Hmean page_fault1-threads-482 7720646.31 ( 0.00%) 7597453.65 ( -1.60%) 7870063.90 ( 1.94%)
> Hmean page_fault1-threads-512 7353458.45 ( 0.00%) 7584407.14 ( 3.14%) 8119539.24 ( 10.42%)
> Stddev page_fault1-processes-2 4086.39 ( 0.00%) 1698.11 ( 58.44%) 1488.13 ( 63.58%)
> Stddev page_fault1-processes-5 1448.69 ( 0.00%) 1616.59 ( -11.59%) 1567.37 ( -8.19%)
> Stddev page_fault1-processes-8 1828.29 ( 0.00%) 2628.59 ( -43.77%) 2701.96 ( -47.79%)
> Stddev page_fault1-processes-12 14073.12 ( 0.00%) 1575.18 ( 88.81%) 4880.93 ( 65.32%)
> Stddev page_fault1-processes-21 4368.35 ( 0.00%) 7865.27 ( -80.05%) 3778.03 ( 13.51%)
> Stddev page_fault1-processes-30 5348.13 ( 0.00%) 11751.43 (-119.73%) 3240.22 ( 39.41%)
> Stddev page_fault1-processes-48 23687.16 ( 0.00%) 7803.01 ( 67.06%) 2635.85 ( 88.87%)
> Stddev page_fault1-processes-79 12779.16 ( 0.00%) 4311.60 ( 66.26%) 22539.03 ( -76.37%)
> Stddev page_fault1-processes-110 21031.04 ( 0.00%) 15115.36 ( 28.13%) 12136.54 ( 42.29%)
> Stddev page_fault1-processes-141 589804.99 ( 0.00%) 1335519.71 (-126.43%) 19560.01 ( 96.68%)
> Stddev page_fault1-processes-172 7033.94 ( 0.00%) 7147.71 ( -1.62%) 11366.64 ( -61.60%)
> Stddev page_fault1-processes-203 6322.20 ( 0.00%) 5035.55 ( 20.35%) 4043.45 ( 36.04%)
> Stddev page_fault1-processes-234 12046.53 ( 0.00%) 24208.37 (-100.96%) 9159.91 ( 23.96%)
> Stddev page_fault1-processes-265 11869.43 ( 0.00%) 13528.26 ( -13.98%) 8943.99 ( 24.65%)
> Stddev page_fault1-processes-296 8918.50 ( 0.00%) 16130.54 ( -80.87%) 5211.80 ( 41.56%)
> Stddev page_fault1-processes-327 101102.64 ( 0.00%) 845864.70 (-736.64%) 16238.99 ( 83.94%)
> Stddev page_fault1-processes-358 2102190.38 ( 0.00%) 11316.00 ( 99.46%) 7508.57 ( 99.64%)
> Stddev page_fault1-processes-389 61012.79 ( 0.00%) 121446.55 ( -99.05%) 18279.64 ( 70.04%)
> Stddev page_fault1-processes-420 2305208.40 ( 0.00%) 2347564.71 ( -1.84%) 3202.77 ( 99.86%)
> Stddev page_fault1-processes-451 20214.37 ( 0.00%) 173800.17 (-759.79%) 492258.35 (-2335.19%)
> Stddev page_fault1-processes-482 236881.21 ( 0.00%) 330501.32 ( -39.52%) 15307.31 ( 93.54%)
> Stddev page_fault1-processes-512 201354.82 ( 0.00%) 207019.93 ( -2.81%) 4900536.90 (-2333.78%)
>
> This is showing there was a impact around the nr_cpus (110 and 141
> processes measured) but the standard deviation around 141 was particularly
~~~~~~~~~
Did you mean threads?
> high in the baseline case taking two passes through lists. It's also
> interesting to note that in most cases that standard deviation is reduced
> by the series even though it's not universally true.
>
> As a side-note, there is also a fair amount of NUMA balancing that takes
> place during this test which further muddies the waters. This is a slightly
> surprising result and I suspect what's happening is that processes are
> getting migrated cross-node as the number of processes exceed a local
> nodes capacity due to load balancing. It might be highlighting a weakness
> in the test itself where it ends up measuring more than one thing (not
> just fault capacity but load balancing effects as individual nodes CPU
> capacity approaches fully busy).
Makes sense.
>
> My main concern when writing this patch was the basic case of one CPU doing
> a lot of frees (exiting, large truncate, large unmap, anything hammering
> on release_pages for a large region etc) suffered from taking two loops
> through lists with all the associated cost of the list manipulations. I
> worried that by trying to optimise for a corner case (all CPUs allocating
> simultaneously), we missed a basic case (one CPU doing a large amount
> of allocating/freeing).
I see.
>
> If possible, it would be nice if you could add something like
> configs/config-io-trunc from mmtests to lkp if it doesn't exist already
> to consider the simple case. As its most basic, all it's doing is
>
> ---8<---
> #!/bin/bash
>
> for i in {1..10}; do
> dd if=/dev/zero of=sparse_file-$i bs=1 count=0 seek=1G &>/dev/null
> cat sparse_file-$i > /dev/null
> done
> sync
>
> # Primary metric
> time rm sparse_file*
> ---8<---
>
> The main difference is that the mmtests will report the time to fault the
> sparse files (bulk simple allocate inserting into page cache) as well as
> the bulk truncate (bulk simple release of page cache).
Thanks for the suggestion.
vm-scalability has a similar test called case-truncate which LKP already uses:
https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git/tree/case-truncate
except in case-truncate, the rm is done concurrently and only the
truncate time is reported. I'll modify the case to make it do the rm in
sequential mode and also report the fault time.
Regards,
Aaron
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