[PATCH mm-unstable v2 0/5] mm: khugepaged cleanups and mTHP prerequisites

[Nico Pache <npache@redhat.com>]

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

V2 Changes:
- patch1: add missing pte_sw_mkyoung [2]
- patch1: the switch to maybe_mkwrite introduced a functional change
  causing pte_mkdirty to no longer run conditionally. switch back to the
  original call format [2]
- patch1: fix minor formatting issues [3]
- patch2: found/added more open-coded is_pmd_order() checks
- patch3: only use the define for cases referring to the khugepaged
  limits. [4]
- patch5: Move the last bits of the new writeback retry logic into
  collapse_single_pmd. My previous version had this logic split across
  madvise_collapse and collapse_single_pmd. [5](Thanks David!)
- did not add review/ack's on patch 1 or 5 due to the above changes.

V1 - https://lore.kernel.org/lkml/20260212021835.17755-1-npache@redhat.com/

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@redhat.com/
[2] - https://lore.kernel.org/lkml/CAA1CXcC7SPkehNLT8FUnnUf6m0vm3GbhZuDZyMMW4X0DHDs6Mg@mail.gmail.com/
[3] - https://lore.kernel.org/lkml/20260212155539.2083102-1-joshua.hahnjy@gmail.com/
[4] - https://lore.kernel.org/lkml/493d7898-c959-42ee-ad09-35ffc631ec21@kernel.org/
[5] - https://lore.kernel.org/lkml/92e9d637-988a-4201-8c8b-c29987b727bb@kernel.org/

Nico Pache (5):
  mm: consolidate anonymous folio PTE mapping into helpers
  mm: introduce is_pmd_order helper
  mm/khugepaged: define COLLAPSE_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         | 206 +++++++++++++++++++++-------------------
 mm/memory.c             |  61 ++++++++----
 mm/mempolicy.c          |   2 +-
 mm/mremap.c             |   2 +-
 mm/page_alloc.c         |   4 +-
 mm/shmem.c              |   3 +-
 9 files changed, 163 insertions(+), 126 deletions(-)

-- 
2.53.0