linux-kernel - Re: [PATCH v3 0/2] __folio

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Message-ID: <8A30F788-2ED9-4F27-867B-BD97D23BB329@nvidia.com>
Date: Thu, 17 Jul 2025 11:54:36 -0400
From: Zi Yan <ziy@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Balbir Singh <balbirs@...dia.com>, David Hildenbrand <david@...hat.com>,
 linux-mm@...ck.org, Hugh Dickins <hughd@...gle.com>,
 Kirill Shutemov <k.shutemov@...il.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] __folio_split() clean up.

On 17 Jul 2025, at 8:40, Lorenzo Stoakes wrote:

> Hm something has gone weird in mm-new with this.
>
> The patches are in the correct order, but the 2/2 patch, 'mm/huge_memory: use
> folio_expected_ref_count() to calculate ref_count.' contains the cover letter
> and has the suffix:
>
>     This patch (of 2):
>
>     Instead of open coding the ref_count calculation, use
>     folio_expected_ref_count()
>
> But immediately prior to it is 1/2 - mm/huge_memory: move unrelated code
> out of __split_unmapped_folio() but with no cover letter reference.
>
> Andrew - has quilt got confused here? :)

Since I am going to send V3 (also include after-split page cache code patch),
maybe Andrew can drop this series and
“mm/huge_memory: refactor after-split (page) cache code”. Hopefully
we can get everything right in V3.

>
> Thanks, Lorenzo
>
> On Mon, Jul 14, 2025 at 01:18:21PM -0400, Zi Yan wrote:
>> Based on the prior discussion[1], this patch improves
>> __split_unmapped_folio() by making it reusable for splitting unmapped
>> folios. This helps avoid the need for a new boolean unmapped parameter
>> to guard mapping-related code.
>>
>> An additional benefit is that __split_unmapped_folio() could be
>> called on after-split folios by __folio_split(). It can enable new split
>> methods. For example, at deferred split time, unmapped subpages can
>> scatter arbitrarily within a large folio, neither uniform nor non-uniform
>> split can maximize after-split folio orders for mapped subpages.
>> The hope is that by calling __split_unmapped_folio() multiple times,
>> a better split result can be achieved.
>>
>> It passed mm selftests.
>>
>>
>> Changelog
>> ===
>> From V2[3]:
>> 1. Code format fixes
>> 2. Restructured code to remove after_split goto label.
>>
>> From V1[2]:
>> 1. Fixed indentations.
>> 2. Used folio_expected_ref_count() to calculate ref_count instead of
>>    open coding.
>>
>>
>> [1] https://lore.kernel.org/linux-mm/94D8C1A4-780C-4BEC-A336-7D3613B54845@nvidia.com/
>> [2] https://lore.kernel.org/linux-mm/20250711030259.3574392-1-ziy@nvidia.com/
>> [2] https://lore.kernel.org/linux-mm/20250711182355.3592618-1-ziy@nvidia.com/
>>
>> Zi Yan (2):
>>   mm/huge_memory: move unrelated code out of __split_unmapped_folio()
>>   mm/huge_memory: use folio_expected_ref_count() to calculate ref_count.
>>
>>  mm/huge_memory.c | 289 +++++++++++++++++++++++------------------------
>>  1 file changed, 142 insertions(+), 147 deletions(-)
>>
>> --
>> 2.47.2
>>


Best Regards,
Yan, Zi