[PATCH mm-unstable v3 0/5] mm: khugepaged cleanups and mTHP prerequisites

[Nico Pache]

The following series contains cleanups and prerequisites for my work on
khugepaged mTHP support [1]. These have been separated out to ease review.

The first patch in the series refactors the page fault folio to pte mapping
and follows a similar convention as defined by map_anon_folio_pmd_(no)pf().
This not only cleans up the current implementation of do_anonymous_page(),
but will allow for reuse later in the khugepaged mTHP implementation.

The second patch adds a small is_pmd_order() helper to check if an order is
the PMD order. This check is open-coded in a number of places. This patch
aims to clean this up and will be used more in the khugepaged mTHP work.
The third patch also adds a small DEFINE for (HPAGE_PMD_NR - 1) which is
used often across the khugepaged code.

The fourth and fifth patch come from the khugepaged mTHP patchset [1].
These two patches include the rename of function prefixes, and the
unification of khugepaged and madvise_collapse via a new
collapse_single_pmd function.

Patch 1:     refactor do_anonymous_page into map_anon_folio_pte_(no)pf
Patch 2:     add is_pmd_order helper
Patch 3:     Add define for (HPAGE_PMD_NR - 1)
Patch 4:     Refactor/rename hpage_collapse
Patch 5:     Refactoring to combine madvise_collapse and khugepaged

Testing:
- Built for x86_64, aarch64, ppc64le, and s390x
- ran all arches on test suites provided by the kernel-tests project
- selftests mm

V3 Changes:
- Patch1: leverage folio_order rather than passing nr_pages into
  map_anon_folio_pte_pf [2]
- Patch 2: fixed conflict with is_pmd_order
- Patch 3: Change COLLAPSE_MAX_PTES_LIMIT to KHUGEPAGED_MAX_PTES_LIMIT [3]
- Patch 4: conflict resolution with other khugepaged patches
- Patch 5: Drop lock_dropped unnecessary change, Dropped Lorenzos RB,
  !triggered_wb in if statement rather than triggered_wb, remove
  unnecessary mmap_locked flipping [4]

V2 - https://lore.kernel.org/all/20260226012929.169479-1-npache@xxxxxxxxxx/
V1 - https://lore.kernel.org/lkml/20260212021835.17755-1-npache@xxxxxxxxxx/

A big thanks to everyone that has reviewed, tested, and participated in
the development process.

[1] - https://lore.kernel.org/all/20260122192841.128719-1-npache@xxxxxxxxxx/
[2] - https://lore.kernel.org/all/7334b702-f6a0-4ccf-8ac6-8426a90d1846@xxxxxxxxxx/
[3] - https://lore.kernel.org/all/25723c0f-c702-44ad-93e9-1056313680cd@xxxxxxxxxx/
[4] - https://lore.kernel.org/all/81ff9caa-50f2-4951-8d82-2c8dcdf3db91@xxxxxxxxxx/

Nico Pache (5):
  mm: consolidate anonymous folio PTE mapping into helpers
  mm: introduce is_pmd_order helper
  mm/khugepaged: define KHUGEPAGED_MAX_PTES_LIMIT as HPAGE_PMD_NR - 1
  mm/khugepaged: rename hpage_collapse_* to collapse_*
  mm/khugepaged: unify khugepaged and madv_collapse with
    collapse_single_pmd()

 include/linux/huge_mm.h |   5 ++
 include/linux/mm.h      |   4 +
 mm/huge_memory.c        |   2 +-
 mm/khugepaged.c         | 187 +++++++++++++++++++++-------------------
 mm/memory.c             |  62 ++++++++-----
 mm/mempolicy.c          |   2 +-
 mm/mremap.c             |   2 +-
 mm/page_alloc.c         |   4 +-
 mm/shmem.c              |   3 +-
 9 files changed, 153 insertions(+), 118 deletions(-)

-- 
2.53.0