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

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Message-ID: <9a0eade4-8981-4379-8260-e673a1803d56@vivo.com>
Date: Fri, 25 Jul 2025 09:47:16 +0800
From: Huan Yang <link@...o.com>
To: "Huang, Ying" <ying.huang@...ux.alibaba.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

在 2025/7/25 09:37, Huang, Ying 写道:
> 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 :-)
I'll remember it. Thanks. :)
>
> If you cannot prove that the optimization has some practical effect,
> it's hard to persuade others for increased complexity.

To be honest, this patch stems from an issue I noticed during code review.

When this patchset was completed, I did put in some effort to find its 
benefits, and it was only

under such an exaggeratedly constructed test scenario that the effect 
could be demonstrated. :(

The actual problem I'm facing has been described in other replies.

It's actually about some anonymous pages and fully COW-ed pages, but 
their avcs haven't been

removed from the anon_vma's RB tree, resulting in inefficient traversal.

Lorenzo has mentioned that he has some bold ideas regarding this, let's 
look forward it. :)

Thanks.

>
> ---
> Best Regards,
> Huang, Ying