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Date: Wed, 23 Feb 2022 19:30:52 +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 Mon, Feb 21, 2022 at 09:38:22PM +0800, Aaron Lu wrote:
> On Fri, Feb 18, 2022 at 12:20:03PM +0800, Aaron Lu wrote:
> > 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.
> >
>
> For the record, these tests don't show any visible performance changes
> on CooperLake.
One thing I just noticed is that, zone lock contention increased to some
extent. I'm not sure if this is worrisome so I suppose I should at least
mention it here.
The nr_task=100% test on the 4 sockets Cooper Lake showed that zone lock
contention increased from 13.56% to 20.16% and for nr_task=16, it
increased from 4.75% to 6.18%.
The reason is probably due to more code are now inside the lock and when
there is contention, it will make things worse. I'm aware of that
nr_task=100% is a rare case and this patchset is meant to improve things
when there is very little contention, which should be the common case.
So I guess that's just the tradeoff we have to make...
Here are the results on performance metric and zone lock metrics:
nr_task=100%
=========================================================================================
tbox_group/testcase/rootfs/kconfig/compiler/nr_task/mode/test/thp_enabled/cpufreq_governor:
lkp-cpl-4sp1/will-it-scale/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/100%/process/page_fault1/never/performance
commit/ucode:
8391e0a7e1728d74faecebf096b446ac5d0a5709/0x7002302 (mm/page_alloc: free pages in a single pass during bulk free)
c000d687ce22252c8ea96e47b4a2add592fbad6c/0x7002302 (mm/page_alloc: simplify how many pages are selected per pcp list during bulk free)
7decb609034044e56cffd1c9971738878467ee96/0x7002402 (mm/page_alloc: Do not prefetch buddies during bulk free)
8391e0a7e1728d74 c000d687ce22252c8ea96e47b4a 7decb609034044e56cffd1c9971
---------------- --------------------------- ---------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
11807831 -0.5% 11750578 -0.3% 11778047 will-it-scale.144.processes
15.44 ± 10% -4.9 10.58 ± 8% +0.6 16.01 ± 5% perf-profile.calltrace.cycles-pp.native_queued_spin_lock_slowpath._raw_spin_lock.rmqueue_bulk.get_page_from_freelist.__alloc_pages
4.72 ± 8% -1.7 2.98 -0.1 4.63 ± 3% perf-profile.calltrace.cycles-pp.native_queued_spin_lock_slowpath._raw_spin_lock.free_pcppages_bulk.free_unref_page_list.release_pages
nr_task=16
=========================================================================================
tbox_group/testcase/rootfs/kconfig/compiler/nr_task/mode/test/thp_enabled/cpufreq_governor/ucode:
lkp-cpl-4sp1/will-it-scale/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/16/process/page_fault1/never/performance/0x7002402
commit:
8391e0a7e1728d74faecebf096b446ac5d0a5709 (mm/page_alloc: free pages in a single pass during bulk free)
c000d687ce22252c8ea96e47b4a2add592fbad6c (mm/page_alloc: simplify how many pages are selected per pcp list during bulk free)
7decb609034044e56cffd1c9971738878467ee96 (mm/page_alloc: Do not prefetch buddies during bulk free)
8391e0a7e1728d74 c000d687ce22252c8ea96e47b4a 7decb609034044e56cffd1c9971
---------------- --------------------------- ---------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
3410615 +0.2% 3416565 +0.2% 3415846 will-it-scale.16.processes
4.83 ± 3% -1.1 3.76 ± 9% -0.4 4.40 ± 4% perf-profile.calltrace.cycles-pp.native_queued_spin_lock_slowpath._raw_spin_lock.rmqueue_bulk.get_page_from_freelist.__alloc_pages
1.35 ± 9% -0.4 0.99 ± 14% -0.2 1.17 ± 3% perf-profile.calltrace.cycles-pp.native_queued_spin_lock_slowpath._raw_spin_lock.free_pcppages_bulk.free_unref_page_list.release_pages
Regards,
Aaron
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