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

["Zi Yan" <ziy@nvidia.com>]

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.

BTW, in your check_huge_shmem(), expect_huge seems to be inverted
compared to other check_huge_xxx().

-- 
Best Regards,
Yan, Zi