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

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Message-ID: <816d77f1-aa8f-4580-b1cd-b8c81f929fdd@linux.alibaba.com>
Date: Thu, 21 Aug 2025 09:11:45 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Zi Yan <ziy@...dia.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 2025/8/20 21:49, Zi Yan wrote:
> 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.

Thanks for the information. khugepaged also does not have this case, so 
it works well for me.