split_huge_page_test can fail for the following reasons:
1. During the test, khugepaged may collapse previously split pages again,
causing intermittent failures.
2. 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(). Moreover, a subsequent
madvise(MADV_HUGEPAGE) call does not split the VMA because it already
has the same advice.
This causes the 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.
Address these issues by applying MADV_NOHUGEPAGE after faulting in the
huge page, preventing khugepaged from collapsing it again, and instead of
relying on /proc/self/smaps, use /proc/self/pagemap and
/proc/kpageflags to detect huge-page mappings and large folios:
1. If hpage_size == pmd_pagesize, check PAGE_IS_HUGE instead of
using check_large_folios(), since only the mapping type matters.
This identifies PMD-mapped huge pages.
2. Otherwise, use check_large_folios() to detect large folios. This
covers mTHP cases.
3. Check the folio flags according to the type of huge page.
Also, current usage of memalign() would result memory area may
unexpectedly merge with an adjacent VMA, causing tests
that inspect it through /proc/self/smaps to fail.
Eliminate this potential source of test flakiness by introducing
alloc_isolated_mem(), which places guard regions before and after the
allocated area to prevent unexpected VMA merging.
This patch based on mm-unstable
---
Changes in v4:
- reparse commit message.
- introduce alloc_isolated_mem().
- make madv_nohuge() helper according to suggestion.
- Link to v3:
https://lore.kernel.org/r/[email protected]
Changes in v3:
- change message in case of failure of madvise() with MADV_NOHUGEPAGE.
- fix collapse_single_mthp (mthp_khugepaged:anon) test case failure.
- Link to v2:
https://lore.kernel.org/all/[email protected]/
Changes in v2:
- rebase to mm-unstable.
- add message in case of failure of madvise() with MADV_NOHUGEPAGE.
- fix wrong setup expected_huge in check_huge_shmem().
- Link to v1:
https://lore.kernel.org/r/[email protected]
---
Yeoreum Yun (3):
kselftest: mm: prevent random failure of huge page split for khugepaged
kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx()
helper
kselftest: mm: introduce alloc_isolated_mem()
tools/testing/selftests/mm/pagemap_ioctl.c | 18 +-
tools/testing/selftests/mm/soft-dirty.c | 6 +-
tools/testing/selftests/mm/split_huge_page_test.c | 27 ++-
tools/testing/selftests/mm/vm_util.c | 212 ++++++++++++++++------
tools/testing/selftests/mm/vm_util.h | 3 +
5 files changed, 192 insertions(+), 74 deletions(-)
---
base-commit: e3b5239afe1b8f0194db7436b17c33e94c1988c4
change-id: 20260820-fix_split-f44939ec44b8
Best regards,
--
Sincerely,
Yeoreum Yun
