[PATCH v5 00/19] selftests/mm: improve khugepaged coverage

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>

khugepaged collapses to mTHP orders since 7.2, and 7.3 added three
selftest cases for it: the generic collapse cases run at one order named
by -c, with the result detected by counting folios of that order.

That leaves the collapse path largely untested.  The suite does not run
where a PMD is 512M.  A folio count cannot say where a collapse landed.
Fixed sleeps cannot tell "not collapsed" from "not scanned yet".  And
nothing exercises collapse under contention.

Close those gaps in order:

 - Make the suite run at a 512M PMD: scale the collapse wait with the PMD
   size, skip what such a PMD cannot serve, make the swapout the swap
   cases depend on deterministic, and keep khugepaged out of the
   MADV_COLLAPSE cases.

 - Detect results per window rather than by count, with folio-order
   helpers in vm_util that are checked against the kernel before any
   collapse test trusts them.

 - Drive khugepaged deterministically: a completion barrier that wakes the
   daemon and waits for a full pass, and a check that one pass yields one
   attributed collapse.

 - Cover collapse at every supported order by default: which window
   collapses, occupancy at both limits, sources that are already large
   folios, and a fork-shared source under concurrent writes.

 - Race collapse against everything that can touch its sources, at both
   occupancy limits and over whole-table zaps, checked by content and by
   the kernel's own assertions.

Everything passes on an unmodified kernel.

Changes since v4:

 - Comments and changelogs rewritten: why, not what (Lorenzo Stoakes,
   Mike Rapoport).
 - Helper names say what they check, one pass budget across the new
   tests, and the review nits taken.
 - The raised collapse wait is measured: a passing run costs the same
   with either budget.
 - Rebased onto mm-unstable; Assisted-by per coding-assistants.rst.

Tested on mm-unstable 20cab322c95c with KASAN, lockdep, DEBUG_VM and
page_table_check, in 16G guests:

  x86-64/4K   khugepaged all:all  104 pass, 11 skip, 0 fail
  arm64/64K   khugepaged all:all  102 pass,  3 skip, 0 fail

folio_order_check, khugepaged_sync_check and khugepaged_race pass on both.

The skips are structural: tmpfs cannot host some file cases, and mixed
sources has no order below the smallest.  arm64 never registers the file
and shmem contexts, having no PMD-order page cache folio.  The default
./khugepaged run there takes about 220 seconds under TCG.

Kiryl Shutsemau (Meta) (19):
  selftests/mm: raise the khugepaged test-case cap
  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: make the swap cases' swapout reliable
  selftests/mm: stop khugepaged during the MADV_COLLAPSE cases
  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: check that one khugepaged pass collapses one window
  selftests/mm: add khugepaged race harness
  selftests/mm: race the 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  | 122 ++++
 tools/testing/selftests/mm/hmm-tests.c        |   1 -
 .../testing/selftests/mm/hugepage_settings.c  |  60 +-
 .../testing/selftests/mm/hugepage_settings.h  |  11 +
 tools/testing/selftests/mm/khugepaged.c       | 485 +++++++++++++++-
 tools/testing/selftests/mm/khugepaged_race.c  | 533 ++++++++++++++++++
 .../selftests/mm/khugepaged_sync_check.c      | 179 ++++++
 tools/testing/selftests/mm/migration.c        |   1 -
 tools/testing/selftests/mm/run_vmtests.sh     |   8 +-
 .../selftests/mm/split_huge_page_test.c       |  62 --
 tools/testing/selftests/mm/vm_util.c          | 147 +++++
 tools/testing/selftests/mm/vm_util.h          |  10 +
 13 files changed, 1519 insertions(+), 103 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: 20cab322c95cea0327215bb81a05df69336032dd
-- 
2.54.0