[PATCH v2 00/17] selftests/mm: improve khugepaged coverage

From: "Kiryl Shutsemau (Meta)" <[email protected]>

mTHP collapse went in for 7.2 with no functional selftest coverage. Every
khugepaged collapse case is PMD-shaped, down to the detection: it reads
smaps AnonHugePages, which cannot see anything below the PMD order.

I am also reworking khugepaged's collapse mechanism, and that wants a suite
worth trusting before the mechanism changes underneath it. Nothing here
depends on the rework: everything passes on an unmodified kernel and
documents what khugepaged already does.

This version sits on top of Baolin's anon mTHP collapse selftests [1], now
in mm-new. His mthp_khugepaged context and per-order detection are what the
new cases need, so they go in there rather than bringing their own.

Four existing cases fail on the environment rather than on the kernel:

 - The collapse wait is a fixed three seconds, whatever a huge page costs
   to build. Scale it with the PMD size.

 - collapse_compound_extreme wants a 512M folio from the fault path. Skip
   it where the PMD is that large.

 - The page cache caps folio order below the PMD order where a PMD is 512M,
   so nothing can hold a PMD-sized page cache folio. Skip the shmem and
   file cases there.

 - The swap cases ask a best-effort MADV_PAGEOUT for an exact swap count.
   Ask again before calling it a failure.

This is why the suite now runs on arm64 with 64K pages.

Then the new coverage:

 - Folio-order helpers in vm_util, and folio_order_check to validate them
   against the kernel before any collapse test trusts them.

 - Four order-parameterized anon collapse cases, plus mixed sources by
   source order, at every supported order by default.

 - A shared-source write race: a co-sharer writing throughout a collapse
   and the collapsing side must not see each other's pages.

 - khugepaged_full_pass(), which steps the daemon one scan at a time
   through the sysfs wake path, and khugepaged_sync_check to hold it to
   exactly one attributed collapse per step.

 - khugepaged_race, racing faults, MADV_DONTNEED, pins, fork and mremap
   against collapse, checked by content and by KASAN and lockdep.

Tested on mm-new (8086604be973), with KASAN, lockdep, DEBUG_VM and
page_table_check, in 16G guests:

  x86-64 4K     190 pass, 1 skip, 0 fail
  arm64 64K     228 pass, 5 skip, 0 fail

The skips are structural: mixed sources declines at the smallest order, and
at 64K collapse_compound_extreme and the shmem components skip as above.

Changes since v1:

 - Rebased onto [1] (Baolin Wang), which this overlapped and which is in
   mm-new now, so this applies on top of it. This series' own -o mode is
   gone in favour of his context.
 - A plain ./khugepaged and ./khugepaged_race now run everything they can:
   every supported order, and every mode, occupancy and pressure axis.  The
   options only narrow that down (Mike Rapoport).
 - The fixes to existing cases come first, then the infrastructure and the
   new tests, each next to what it validates (Mike Rapoport).
 - The completion barrier helper comes before the tests that use it, so no
   case carries a throwaway implementation of it (Mike Rapoport).
 - Changelogs and comments rewritten to be read rather than parsed
   (Mike Rapoport).
 - One new patch: retry the swapout, which is what made
   collapse_max_ptes_swap flaky at 64K.
 - Dropped the swap-skip patch, an equivalent has landed
   (Alexander Gordeev).
 - Review fixes: masked failures, system state left behind on bail-out
   paths, arguments taken on trust (Sashiko).

[1] https://lore.kernel.org/all/[email protected]

Kiryl Shutsemau (Meta) (17):
  selftests/mm: skip collapse_compound_extreme where the PMD is too
    large
  selftests/mm: scale khugepaged's collapse wait with the PMD size
  selftests/mm: skip khugepaged page cache cases without a PMD folio
  selftests/mm: retry the swapout the khugepaged swap cases rely on
  selftests/mm: move is_backed_by_folio() into vm_util
  selftests/mm: add folio-order check for address ranges
  selftests/mm: add folio-order detection self-check
  selftests/mm: add khugepaged completion barrier helper
  selftests/mm: add order-parameterized khugepaged collapse cases
  selftests/mm: parameterize the mixed-source collapse case by source
    order
  selftests/mm: cover a shared-source collapse write race
  selftests/mm: run every supported collapse order by default
  selftests/mm: verify synchronous khugepaged driving is attributable
  selftests/mm: add khugepaged race harness
  selftests/mm: race collapse of windows with holes
  selftests/mm: add memory-pressure threads to the khugepaged race
    harness
  selftests/mm: zap whole PTE tables in the khugepaged race harness

 tools/testing/selftests/mm/Makefile           |   3 +
 .../testing/selftests/mm/folio_order_check.c  | 137 +++++
 tools/testing/selftests/mm/hmm-tests.c        |   1 -
 .../testing/selftests/mm/hugepage_settings.c  |  72 ++-
 .../testing/selftests/mm/hugepage_settings.h  |   3 +
 tools/testing/selftests/mm/khugepaged.c       | 466 +++++++++++++-
 tools/testing/selftests/mm/khugepaged_race.c  | 571 ++++++++++++++++++
 .../selftests/mm/khugepaged_sync_check.c      | 217 +++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   8 +-
 .../selftests/mm/split_huge_page_test.c       |  62 --
 tools/testing/selftests/mm/vm_util.c          | 145 +++++
 tools/testing/selftests/mm/vm_util.h          |  10 +
 12 files changed, 1599 insertions(+), 96 deletions(-)
 create mode 100644 tools/testing/selftests/mm/folio_order_check.c
 create mode 100644 tools/testing/selftests/mm/khugepaged_race.c
 create mode 100644 tools/testing/selftests/mm/khugepaged_sync_check.c


base-commit: 8086604be9733378461a5534c39cb72635226b23
-- 
2.54.0