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

[Yeoreum Yun]

> 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().
> >
> > 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@xxxxxxxxxxxxxxxxx/
>

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@xxxxxxxxxxxxxxxxx/


> >
> >   - nr_hpages > 0: check all of pages in the range are huge page.
> >   - nr_hpages < 0: check all of pages in the range are not huge page.
> >   - nr_hpages == 0: invalid.
> >
> > Reported-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> > ---
> >  tools/testing/selftests/mm/khugepaged.c           |  26 ++---
> >  tools/testing/selftests/mm/split_huge_page_test.c |   6 +-
> >  tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
> >  tools/testing/selftests/mm/vm_util.h              |   1 +
> >  4 files changed, 131 insertions(+), 37 deletions(-)
> >
> 
> 
> -- 
> Best Regards,
> Yan, Zi
> 

-- 
Sincerely,
Yeoreum Yun