linux-kernel - Re: [PATCH v5 4/5] selftests/mm: add check_after_split_folio

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Message-ID: <A5A3C9E5-7E90-4EB4-878F-D5143FE0F349@nvidia.com>
Date: Wed, 20 Aug 2025 09:49:45 -0400
From: Zi Yan <ziy@...dia.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Wei Yang <richard.weiyang@...il.com>, wang lian <lianux.mm@...il.com>,
 David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.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>, Vlastimil Babka <vbabka@...e.cz>,
 Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Shuah Khan <shuah@...nel.org>,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 4/5] selftests/mm: add check_after_split_folio_orders()
 helper.

On 20 Aug 2025, at 5:22, Baolin Wang wrote:

> On 2025/8/19 02:46, Zi Yan wrote:
>> The helper gathers a folio order statistics of folios within a virtual
>> address range and checks it against a given order list. It aims to provide
>> a more precise folio order check instead of just checking the existence of
>> PMD folios.
>>
>> The helper will be used the upcoming commit.
>>
>> Signed-off-by: Zi Yan <ziy@...dia.com>
>> ---
>
> I tested this patch, and it works for me.
> Tested-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

Thanks.

>
> By the way, I moved gather_after_split_folio_orders() to the vm_util.c file as a helper for mTHP collapse checks in my patchset[1]. I'm not sure whether you need to move gather_after_split_folio_orders() to vm_util.c in this patch, or if I should move it in my patchset.

Feel free to move it in your patchset. My initial version has it in vm_util.c, but
I realized that its implementation is very limited to folio split check and moved
it to split_huge_page_test.c. If you find it suitable for your test cases, feel
free to move it. Just note that the code does not handle memremapped THP, since
it only checks page flags without checking the PFN. So when a vaddr range is mapped
to a THP/mTHP head page and some other THP/mTHP tail pages, the code just treats
the whole vaddr range as if it is mapped to a single THP/mTHP and gets a wrong
order. After-split folios do not have this concern, so
gather_after_split_folio_orders() is simplified to not handle such cases.

>
> [1] https://lore.kernel.org/all/955e0b9682b1746c528a043f0ca530b54ee22536.1755677674.git.baolin.wang@linux.alibaba.com/

--
Best Regards,
Yan, Zi