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

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Message-ID: <e9bb93a6-1e95-40e5-ad10-a60d80735432@redhat.com>
Date: Thu, 24 Jul 2025 11:12:11 +0200
From: David Hildenbrand <david@...hat.com>
To: Huan Yang <link@...o.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.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>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 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

On 24.07.25 11:09, Huan Yang wrote:
> 
> 在 2025/7/24 16:59, David Hildenbrand 写道:
>> On 24.07.25 10:44, 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.
>>
>> I absolutely detest (ab)using page types for that, so no from my side 
>> unless I am missing something important.
>>
>>>
>>> In my self-constructed test scenario, the migration time can be reduced
>>
>> How relevant is that in practice?
> 
> IMO, any folio mapped < nr vma in mapping(anon_vma, addresss_space), 
> will benefit from this.
> 
> So, all pages that have been COW-ed by child processes can be skipped.

For small anon folios, you could use the anon-exclusive marker to derive 
"there can only be a single mapping".

It's stored alongside the migration entry.

So once you restored that single migration entry, you can just stop the 
walk.

-- 
Cheers,

David / dhildenb