Re: [PATCH v5 08/19] selftests/mm: add folio-order check for address ranges

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 9/10/26 6:45 PM, Kiryl Shutsemau wrote:
> On Wed, Sep 09, 2026 at 06:01:13PM +0800, Baolin Wang wrote:
>>
>>
>> On 9/8/26 8:50 PM, Kiryl Shutsemau wrote:
>>> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
>>>
>>> An mTHP collapse test needs to know that a range is backed by folios of the
>>> target order, and that they sit where a collapse would put them.  Nothing
>>> answers that today: is_backed_by_folio() classifies the folio behind a
>>> single page, and check_huge_anon() reads smaps AnonHugePages, which only
>>> accounts PMD mappings.
>>
>> Have you checked check_large_folios() in vm_util.c? It seems to meet your
>> requirements, or am I missing something?
> 
> The changelog is out of date, sorry: since 6dedaf0d46a9 check_huge_anon()
> counts mTHP folios through check_large_folios() rather than reading
> smaps, and it is what check_huge() already uses for mthp_khugepaged.
> 
> It could do this job too, called once per window.
> 
> What is_range_backed_by_order() adds is alignment check: the folio has
> to sit at the window start. And check_large_folios() reopens two fds per
> per call which kinda wasteful.

OK. But can we extend the check_huge_xxx() functions to meet your 
requirements, for example by adding a check_aligned_huge_xxx() that 
wraps the underlying implementation of check_large_folios()?

I still find it confusing that khugepaged.c has two separate sets of 
functions for checking large folios.

Also, Yeoreum has also extended check_large_folios() further[1].

[1] 
https://lore.kernel.org/all/20260907-fix_split-v5-2-822b810458bc@arm.com/