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Date: Thu, 18 Jun 2020 14:16:26 +0800
From: Xing Zhengjun <zhengjun.xing@...ux.intel.com>
To: Johannes Weiner <hannes@...xchg.org>,
kernel test robot <rong.a.chen@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Minchan Kim <minchan@...nel.org>,
Rik van Riel <riel@...riel.com>,
LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org
Subject: Re: [LKP] Re: [mm] 1431d4d11a: vm-scalability.throughput -11.5%
regression
On 6/16/2020 10:45 PM, Johannes Weiner wrote:
> On Tue, Jun 16, 2020 at 03:57:50PM +0800, kernel test robot wrote:
>> Greeting,
>>
>> FYI, we noticed a -11.5% regression of vm-scalability.throughput due to commit:
>>
>>
>> commit: 1431d4d11abb265e79cd44bed2f5ea93f1bcc57b ("mm: base LRU balancing on an explicit cost model")
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
> That's a really curious result.
>
> An bit of an increase in system time is expected in the series as a
> whole:
>
> 1. When thrashing is detected in the file cache, it intentionally
> makes more effort to find reclaimable anon pages than before - in an
> effort to converge on a stable state that has *neither* page reclaim
> nor refault IO.
>
> 2. There are a couple of XXX about unrealized lock batching
> opportunities. Those weren't/aren't expected to have too much of a
> practical impact, and require a bit more infrastructure work that
> would have interferred with other ongoing work in the area.
>
> However, this patch in particular doesn't add any locked sections (it
> adds a function call to an existing one, I guess?), and the workload
> is doing streaming mmapped IO and shouldn't experience any thrashing.
>
> In addition, we shouldn't even scan anon pages - from below:
>
>> swap_partitions:
>> rootfs_partition: "/dev/disk/by-id/wwn-0x5000c50067b47753-part1"
>
> Does that mean that no swap space (not even a file) is configured?
>
In this case, the swap is disabled (if enabled, you should find the
"swap:" in the job file), "swap_patitions:" is just the description of
the hardware.
>> in testcase: vm-scalability
>> on test machine: 160 threads Intel(R) Xeon(R) CPU E7-8890 v4 @ 2.20GHz with 256G memory
>> with following parameters:
>>
>> runtime: 300s
>> test: lru-file-mmap-read
>> cpufreq_governor: performance
>> ucode: 0xb000038
>>
>> test-description: The motivation behind this suite is to exercise functions and regions of the mm/ of the Linux kernel which are of interest to us.
>> test-url: https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git/
>>
>>
>>
>> If you fix the issue, kindly add following tag
>> Reported-by: kernel test robot <rong.a.chen@...el.com>
>>
>>
>> Details are as below:
>> -------------------------------------------------------------------------------------------------->
>>
>>
>> To reproduce:
>>
>> git clone https://github.com/intel/lkp-tests.git
>> cd lkp-tests
>> bin/lkp install job.yaml # job file is attached in this email
>> bin/lkp run job.yaml
>>
>> =========================================================================================
>> compiler/cpufreq_governor/kconfig/rootfs/runtime/tbox_group/test/testcase/ucode:
>> gcc-9/performance/x86_64-rhel-7.6/debian-x86_64-20191114.cgz/300s/lkp-bdw-ex2/lru-file-mmap-read/vm-scalability/0xb000038
>>
>> commit:
>> a4fe1631f3 ("mm: vmscan: drop unnecessary div0 avoidance rounding in get_scan_count()")
>> 1431d4d11a ("mm: base LRU balancing on an explicit cost model")
>>
>> a4fe1631f313f75c 1431d4d11abb265e79cd44bed2f
>> ---------------- ---------------------------
>> %stddev %change %stddev
>> \ | \
>> 0.23 ± 2% +11.7% 0.26 vm-scalability.free_time
>
> What's free_time?
The average of the time to free memory(unit: second) , you can see the
output of vm-scalability(
https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git/)
benchamrk log "xxxxxxx usecs to free memory"
>
>> 103991 -11.6% 91935 vm-scalability.median
>> 20717269 -11.5% 18336098 vm-scalability.throughput
>> 376.47 +8.3% 407.78 vm-scalability.time.elapsed_time
>> 376.47 +8.3% 407.78 vm-scalability.time.elapsed_time.max
>> 392226 +7.2% 420612 vm-scalability.time.involuntary_context_switches
>> 11731 +4.4% 12247 vm-scalability.time.percent_of_cpu_this_job_got
>> 41005 +14.5% 46936 vm-scalability.time.system_time
>> 3156 -4.8% 3005 vm-scalability.time.user_time
>> 52662860 ± 5% -14.0% 45266760 ± 5% meminfo.DirectMap2M
>> 4.43 -0.5 3.90 ± 2% mpstat.cpu.all.usr%
>> 1442 ± 5% -14.9% 1227 ± 10% slabinfo.kmalloc-rcl-96.active_objs
>> 1442 ± 5% -14.9% 1227 ± 10% slabinfo.kmalloc-rcl-96.num_objs
>> 37.50 ± 2% -7.3% 34.75 vmstat.cpu.id
>> 57.25 +5.2% 60.25 vmstat.cpu.sy
>> 54428 ± 60% -96.5% 1895 ±173% numa-meminfo.node1.AnonHugePages
>> 116516 ± 48% -88.2% 13709 ± 26% numa-meminfo.node1.AnonPages
>> 132303 ± 84% -88.9% 14731 ± 61% numa-meminfo.node3.Inactive(anon)
>
> These counters capture present state, not history. Are these averages
> or snapshots? If snapshots, when are they taken during the test?
These are averages.
>
>> 311.75 ± 8% +16.0% 361.75 ± 2% numa-vmstat.node0.nr_isolated_file
>> 29136 ± 48% -88.4% 3367 ± 24% numa-vmstat.node1.nr_anon_pages
>> 35935841 ± 6% -17.0% 29839972 ± 6% numa-vmstat.node2.numa_foreign
>> 33046 ± 84% -89.1% 3595 ± 61% numa-vmstat.node3.nr_inactive_anon
>> 33046 ± 84% -89.1% 3596 ± 61% numa-vmstat.node3.nr_zone_inactive_anon
>> 21.43 ± 15% +79.4% 38.44 ± 54% sched_debug.cfs_rq:/.load_avg.avg
>> 95.92 ± 9% +96.7% 188.64 ± 67% sched_debug.cfs_rq:/.load_avg.stddev
>> 36.18 ± 7% +13.6% 41.10 ± 4% sched_debug.cfs_rq:/.nr_spread_over.avg
>> 1075687 ±102% +233.3% 3585792 ± 70% sched_debug.cfs_rq:/.spread0.avg
>> 2865813 ± 41% +87.3% 5367329 ± 42% sched_debug.cfs_rq:/.spread0.max
>> -6253423 -61.1% -2430118 sched_debug.cfs_rq:/.spread0.min
>> 351.68 ± 8% -14.8% 299.58 ± 6% sched_debug.cpu.sched_goidle.avg
>> 9441 ± 11% -21.9% 7376 ± 7% sched_debug.cpu.sched_goidle.max
>> 54.46 ± 5% -19.5% 43.82 ± 6% sched_debug.cpu.sched_goidle.min
>> 873.06 ± 8% -19.2% 705.36 ± 4% sched_debug.cpu.sched_goidle.stddev
>> 898.25 ± 10% -15.5% 759.25 ± 12% proc-vmstat.kswapd_low_wmark_hit_quickly
>> 108483 +4.0% 112790 proc-vmstat.nr_active_anon
>> 1006 ± 4% +9.3% 1099 ± 2% proc-vmstat.nr_isolated_file
>> 72985192 +4.5% 76275208 proc-vmstat.nr_mapped
>> 634868 +5.0% 666703 ± 2% proc-vmstat.nr_page_table_pages
>> 106506 +3.6% 110328 proc-vmstat.nr_shmem
>> 108486 +4.0% 112792 proc-vmstat.nr_zone_active_anon
>> 7453 ± 42% +67.4% 12474 ± 12% proc-vmstat.numa_hint_faults
>> 1597 ± 5% -8.8% 1457 ± 6% proc-vmstat.pageoutrun
>> 55272 +3.6% 57288 proc-vmstat.pgactivate
>> 1.603e+09 -2.7% 1.56e+09 proc-vmstat.pgscan_direct
>> 2.935e+08 ± 3% +13.1% 3.32e+08 ± 2% proc-vmstat.pgscan_kswapd
>
> More scan activity. The patch can affect the scan ratio between anon
> and file, so this only makes sense when there is swap space configured
> and anon pages are actually scanned.
>
> Would it be possible to capture deltas of the new pgscan_anon &
> pgscan_file vmstat counters? As well as the workingset_* ones?
>
In fact, all the data supported by the vmstat will be captured, but it
only shows the deltas > 1%, for pgscan_file the delta should < 1%.
> Thanks!
> _______________________________________________
> LKP mailing list -- lkp@...ts.01.org
> To unsubscribe send an email to lkp-leave@...ts.01.org
>
--
Zhengjun Xing
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