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Message-ID: <20220217093113.GU3366@techsingularity.net>
Date: Thu, 17 Feb 2022 09:31:13 +0000
From: Mel Gorman <mgorman@...hsingularity.net>
To: Aaron Lu <aaron.lu@...el.com>
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 09:53:08AM +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
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 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
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
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).
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).
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.
--
Mel Gorman
SUSE Labs
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