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.
Since check_huge_shmem() was required to distinguish shmem huge pages
because /proc/self/smaps reports them using a dedicated “ShmemPmdMapped”
entry, as opposed to “FilePmdMapped” for file-backed huge pages.
Now that /proc/self/smaps is no longer used to detect huge pages and
/proc/kpageflags is used instead, it is sufficient to distinguish
between file-backed and anonymous pages since the ShmemPmdMapped is also
kind of file-backed.
Therefore, remove check_huge_shmem() and use check_huge_file() instead.
This patch based on mm-unstable
---
Changes in v6:
- drop alloc_isolated_mem() patch.
- remove check_huge_shmem().
- Link to v5:
https://lore.kernel.org/r/[email protected]
Changes in v5:
- rename madv_nohuge() to disable_khugepaged().
- Link to v4:
https://lore.kernel.org/r/[email protected]
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: remove check_huge_shmem()
tools/testing/selftests/mm/folio_split_race_test.c | 2 +-
tools/testing/selftests/mm/khugepaged.c | 5 +-
tools/testing/selftests/mm/split_huge_page_test.c | 19 +++
tools/testing/selftests/mm/uffd-common.c | 4 +-
tools/testing/selftests/mm/vm_util.c | 134 ++++++++++++---------
tools/testing/selftests/mm/vm_util.h | 1 -
6 files changed, 104 insertions(+), 61 deletions(-)
---
base-commit: 6b41451631cabf9ea3b384c2a099088e1598f963
change-id: 20260820-fix_split-f44939ec44b8
Best regards,
--
Sincerely,
Yeoreum Yun
