Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper
From: Baolin Wang
Date: Thu Aug 20 2026 - 21:19:54 EST
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@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/
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.