linux-kernel - Re: [RFC PATCH 0/9] introduce PGTY_mgt_entry page

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Message-ID: <87bjp93vb6.fsf@DESKTOP-5N7EMDA>
Date: Fri, 25 Jul 2025 09:37:01 +0800
From: "Huang, Ying" <ying.huang@...ux.alibaba.com>
To: Huan Yang <link@...o.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,  Andrew Morton
 <akpm@...ux-foundation.org>,  David Hildenbrand <david@...hat.com>,  Rik
 van Riel <riel@...riel.com>,  "Liam R. Howlett" <Liam.Howlett@...cle.com>,
  Vlastimil Babka <vbabka@...e.cz>,  Harry Yoo <harry.yoo@...cle.com>,  Xu
 Xin <xu.xin16@....com.cn>,  Chengming Zhou <chengming.zhou@...ux.dev>,
  Mike Rapoport <rppt@...nel.org>,  Suren Baghdasaryan <surenb@...gle.com>,
  Michal Hocko <mhocko@...e.com>,  Zi Yan <ziy@...dia.com>,  Matthew Brost
 <matthew.brost@...el.com>,  Joshua Hahn <joshua.hahnjy@...il.com>,  Rakie
 Kim <rakie.kim@...com>,  Byungchul Park <byungchul@...com>,  Gregory Price
 <gourry@...rry.net>,  Alistair Popple <apopple@...dia.com>,  "Matthew
 Wilcox (Oracle)" <willy@...radead.org>,  Christian Brauner
 <brauner@...nel.org>,  Usama Arif <usamaarif642@...il.com>,  Yu Zhao
 <yuzhao@...gle.com>,  Baolin Wang <baolin.wang@...ux.alibaba.com>,
  linux-mm@...ck.org,  linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/9] introduce PGTY_mgt_entry page_type

Huan Yang <link@...o.com> writes:

> 在 2025/7/24 17:15, Lorenzo Stoakes 写道:

[snip]

>> On Thu, Jul 24, 2025 at 04:44:28PM +0800, Huan Yang wrote:
>>> Summary
>>> ==
>>> This patchset reuses page_type to store migrate entry count during the
>>> period from migrate entry setup to removal, enabling accelerated VMA
>>> traversal when removing migrate entries, following a similar principle to
>>> early termination when folio is unmapped in try_to_migrate.
>>>
>>> In my self-constructed test scenario, the migration time can be reduced
>>> from over 150+ms to around 30+ms, achieving nearly a 70% performance
>>> improvement. Additionally, the flame graph shows that the proportion of
>>> remove_migration_ptes can be reduced from 80%+ to 60%+.
>> This sounds completely contrived. I don't even know if you have a use case
>> here.
>
> The test case I provided does have an amplified effect, but the
> optimization it demonstrates is real. It's just that when scaled up to
> the system level, the effect becomes difficult to observe.
>

It's more important to sell your problems than selling your code :-)

If you cannot prove that the optimization has some practical effect,
it's hard to persuade others for increased complexity.

---
Best Regards,
Huang, Ying