[PATCH v3 0/3] Add hugetlb MADV_DONTNEED support

[Mike Kravetz]

Userfaultfd selftests for hugetlb does not perform UFFD_EVENT_REMAP
testing.  However, mremap support was recently added in commit
550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed
vma").  While attempting to enable mremap support in the test, it was
discovered that the mremap test indirectly depends on MADV_DONTNEED.

madvise does not allow MADV_DONTNEED for hugetlb mappings.  However,
that is primarily due to the check in can_madv_lru_vma().  By simply
removing the check and adding huge page alignment, MADV_DONTNEED can
be made to work for hugetlb mappings.

Do note that there is no compelling use case for adding this support.
This was discussed in the RFC [1].  However, adding support makes sense
as it is fairly trivial and brings hugetlb functionality more in line
with 'normal' memory.

After enabling support, add selftest for MADV_DONTNEED as well as
MADV_REMOVE.  Then update userfaultfd selftest.

If new functionality is accepted, then madvise man page will be updated
to indicate hugetlb is supported.  It will also be updated to clarify
what happens to the passed length argument.

v2 -> v3
- Force start huge page alignment, extend length to huge page size. David
- Added more selftests to verify alignment.
- Remove double check for hugetlb vma. Peter

v1 -> v2
- Use is_vm_hugetlb_page() instead of open coding vma hugetlb check.
- Add new test to .gitignore and use meaningful symbolic names (#define)
  for constants used in test.  Shuah
- Updated help text in userfaultfd test and modified run_vmtests to not
  pass in a file for userfaultfd hugetlb test.  Axel
- Added Reviewed-by for selftest patches.

RFC -> v1
- Fixed alignment issues when calling zap_page_range.  Naoya
- Added checks for invalid arguments and misalignment to selftest.

[1] https://lore.kernel.org/linux-mm/20220113180308.15610-1-mike.kravetz@xxxxxxxxxx/

Mike Kravetz (3):
  mm: enable MADV_DONTNEED for hugetlb mappings
  selftests/vm: add hugetlb madvise MADV_DONTNEED MADV_REMOVE test
  userfaultfd/selftests: enable hugetlb remap and remove event testing

 mm/madvise.c                                 |  33 +-
 tools/testing/selftests/vm/.gitignore        |   1 +
 tools/testing/selftests/vm/Makefile          |   1 +
 tools/testing/selftests/vm/hugetlb-madvise.c | 410 +++++++++++++++++++
 tools/testing/selftests/vm/run_vmtests.sh    |  15 +-
 tools/testing/selftests/vm/userfaultfd.c     |  69 ++--
 6 files changed, 490 insertions(+), 39 deletions(-)
 create mode 100644 tools/testing/selftests/vm/hugetlb-madvise.c

-- 
2.34.1