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Message-ID: <ef637fe1-436e-4003-86fb-47f651433f7b@fujitsu.com>
Date: Tue, 8 Jul 2025 02:26:54 +0000
From: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To: "Huang, Ying" <ying.huang@...ux.alibaba.com>
CC: "linux-mm@...ck.org" <linux-mm@...ck.org>, "Huang, Ying"
<ying.huang@...el.com>, "akpm@...ux-foundation.org"
<akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "Yasunori Gotou (Fujitsu)"
<y-goto@...itsu.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra
<peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
<vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
"lkp@...el.com" <lkp@...el.com>
Subject: Re: [PATCH RFC v2] mm: memory-tiering: Fix PGPROMOTE_CANDIDATE
accounting
On 08/07/2025 09:14, Huang, Ying wrote:
> "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com> writes:
>
>> Hi,
>>
>>
>> On 25/06/2025 10:13, Li Zhijian wrote:
>>> V2:
>>> Fix compiling error # Reported by LKP
>>>
>>> As Ying suggested, we need to assess whether this change causes regression.
>>> However, considering the stringent conditions this patch involves,
>>> properly evaluating it may be challenging, as the outcomes depend on your
>>> perspective. Much like in a zero-sum game, if someone benefits, another
>>> might lose.
>>>
>>> If there are subsequent results, I will update them here.
>>
>> I ran memhog + pmbench to evaluate the impact of the patch(3 runs [1] for each kernel).
>>
>> The results show an approximate 4% performance increase in pmbench after applying this patch.
>>
>> Average pmbench-access max-promotion-rate
>> Before: 7956805 pages/sec 168301 pages/sec
>> After: 8313666 pages/sec (+4.4%) 207149 pages/sec
>
> It's hard for me to understand why performance increases because of
> higher promotion rate, while the expected behavior is more promotion
> rate limiting.
Good question.
Above max-promotion-rate means the maximum rate during the WHOLE pmbench period which
can not indicate the total promoted pages.
Allow me to present each sample [0] recorded per second during the pmbench duration, as exemplified below:
| AFTER |VS | BEFORE |
------------+-------------------------+++++------------------------|
| Timestamp | pgprom/s | pgdem/s | | pgprom/s | pgdem/s |
|-----------|-------------|-----------|---|------------|-----------|
| 1 | 122977 | 0 | | 123051 | 0 |
| 2 | 50171 | 0 | | 50159 | 0 |
| 3 | 18 | 0 | | 28 | 0 |
| 4 | 16647 | 0 | | 0 | 0 |
| 5 | 207149.5 | 0 | | 78895 | 0 |
| 6 | 193411 | 161521 | | 168301 | 8702 |
| 7 | 52464 | 53989 | | 42294 | 39108 |
| 8 | 5133 | 2627 | | 0 | 0 |
| 9 | 24 | 8 | | 3875 | 6213 |
| 10 | 0 | 0 | | 45513 | 43260 |
| 11 | 0 | 0 | | 36600 | 44982 |
| 12 | 0 | 0 | | 21091 | 11631 |
| 13 | 0 | 0 | | 12276 | 10719 |
| 14 | 0 | 0 | | 149699 | 149400 |
| 15 | 0 | 0 | | 4026 | 4933 |
| 16 | 0 | 0 | | 3780 | 0 |
| 17 | 0 | 0 | | 2 | 0 |
| 18 | 0 | 0 | | 0 | 0 |
| 19 | 0 | 0 | | 0 | 0 |
| 20 | 0 | 0 | | 0 | 0 |
| 21 | 0 | 0 | | 62 | 0 |
| 22 | 0 | 0 | | 2016 | 0 |
| 23 | 0 | 0 | | 0 | 0 |
| 24 | 0 | 0 | | 62 | 0 |
| 25 | 8308 | 0 | | 1 | 0 |
| 26 | 220 | 0 | | 0 | 0 |
| 27 | 0 | 0 | | 1995.05 | 0 |
| 28 | 0 | 0 | | 1 | 0 |
| 29 | 5791 | 0 | | 0 | 0 |
| 30 | 0 | 0 | | 62 | 0 |
------------+-------------------------+++++------------------------|
| total | 662313.5 | 218145 | | 743789.05 | 318948 |
| max | 207149.5 | 161521 | | 168301 | 149400 |
------------+-------------------------+++++------------------------|
| pmbench | 8416250 |VS | 8079500 |
As far as I can tell, the higher pmbench scores applied-patch may be attributed to
a reduction in the total number of promoted pages in the entire pmbench execution period.
(Similar circumstances were observed in the results of other tests conducted)
[0]
before:
https://github.com/zhijianli88/misc/blob/main/20250627/promotion-evaluation/without-patch/pmbench-1750988862.log
https://github.com/zhijianli88/misc/blob/main/20250627/promotion-evaluation/without-patch/sar-1750988862.log
after:
https://github.com/zhijianli88/misc/blob/main/20250627/promotion-evaluation/with-patch/pmbench-1750988291.log
https://github.com/zhijianli88/misc/blob/main/20250627/promotion-evaluation/with-patch/sar-1750988291.log
Thanks
Zhijian
>
>> The detailed logs are available at [2].
>>
>> [1] https://github.com/zhijianli88/misc/blob/main/20250627/promotion-evaluation/reproduce.sh
>> [2] https://github.com/zhijianli88/misc/tree/main/20250627/promotion-evaluation
>
> [snip]
>
> ---
> Best Regards,
> Huang, Ying
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