Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

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

On 8/21/26 8:26 AM, Yeoreum Yun wrote:
> On Thu, Aug 20, 2026 at 08:09:12PM -0400, Zi Yan wrote:
>> On Thu Aug 20, 2026 at 5:26 PM EDT, Yeoreum Yun wrote:
>>>> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
>>>>> Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
>>>>> glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
>>>>> made by memalign().
>>
>> I just googled the commit and find that Dev did that. ;)
>>
>>>>>
>>>>> The underlying VMA may start at a different address from the aligned
>>>>> address returned by memalign(). Furthermore, a subsequent
>>>>> madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
>>>>> already set.
>>>>>
>>>>> This causes split_huge_page_test to fail because the check_huge_xxx()
>>>>> helpers incorrectly require the address returned by memalign() to
>>>>> match the VMA start address reported in /proc/self/smaps.
>>>>>
>>>>> Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
>>>>> /proc/self/smaps to detect huge pages and change the meaning of
>>>>> check_huge_xxx()'s nr_hpages argument:
>>>>
>>>> Have you checked Baolin's patches[1] in mm-new? They resue
>>>> gather_after_split_folio_orders() to reimplement check_huge_xxx(), also
>>>> based on pagemap and kpageflags. Does it fix the issue?
>>>>
>>>> [1] https://lore.kernel.org/all/cover.1785985999.git.baolin.wang@linux.alibaba.com/
>>>>
>>>
>>> Unfortunately, No. since __check_pmd_huge() in check_huge_xxx() still use
>>> /proc/self/smaps [1] for pmd THP, it still has problem though ths patch
>>> series applied.
>>>
>>> [1] https://lore.kernel.org/all/56b16691f605426b33b5cf47319233de6127a6b3.1785985999.git.baolin.wang@linux.alibaba.com/
>>
>> In that case, is it possible to use and extend check_large_folios() for
>> all check_huge_xxx()? You still need pagemap_scan_get_categories() to
>> check PAGE_IS_HUGE to identify huge mappings. Or at least
>> check_huge_xxx() in your patch can share most of the code.
> 
> Agree. but TBH, I think check_large_folios() can replace checking
> PAGE_IS_HUGE and keep the later part to check wehther PAGE_IS_FILE
> and SWAPBACKED according to check_huge_xxx().
> 
> BTW, Should I do this after [1] is merged into mm-unstable?

This series is already in mm-unstable, please rebase your patchset on 
mm-unstable branch. Moreover, we've extended check_huge_xxx() to support 
mTHP, so I don't think you need to change the meaning of 'nr_hpages' 
argument.