linux-kernel - Re: [PATCH RFC v2] mm: memory-tiering: Fix PGPROMOTE

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Message-ID: <87tt3nxz4x.fsf@DESKTOP-5N7EMDA>
Date: Tue, 08 Jul 2025 09:14:06 +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:

> 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.

> 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