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Message-ID: <87zfdfwg8h.fsf@DESKTOP-5N7EMDA> Date: Tue, 08 Jul 2025 10:47:42 +0800 From: "Huang, Ying" <ying.huang@...ux.alibaba.com> To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.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 "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com> writes: > 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 > Check the usage of PGPROMOTE_CANDIDATE again. It is used not only by rate limiting, but also promotion threshold adjustment, please take a look at numa_promotion_adjust_threshold(). Which may have larger influence on performance. After checking the threshold adjustment code, I think the changes in this patch may confuse threshold adjustment. [snip] --- Best Regards, Huang, Ying
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