[PATCH mm-unstable v1 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:     rename hpage_collapse to 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

V1 Changes (for patches coming from [1]):
- Refactor do_anonymous_page() and add helpers for use in mthp series
- moved is_pmd_order patch to this series [2]
- added a define for HPAGE_PMD_NR - 1
- moved rename to this series [3]
- Dropped acks/review-by on PATCH 5 given [4]
- moved unification patch to this series [4]. I also had to make some
   modifications from my previous version which include moving the new
   madvise_collapse writeback retry logic into the collapse_single_pmd
   function. This prevents a potential UAF bug I introduced in my v14 when
   handling the conflict. [5][6]

A big thanks to everyone that has reviewed, tested, and participated in
the development process. Its been a great experience working with all of
you on this endeavour.

[1] - https://lore.kernel.org/all/20260122192841.128719-1-npache@xxxxxxxxxx/
[2] - https://lore.kernel.org/all/20260122192841.128719-2-npache@xxxxxxxxxx/
[3] - https://lore.kernel.org/all/20260122192841.128719-3-npache@xxxxxxxxxx/
[4] - https://lore.kernel.org/all/20260122192841.128719-4-npache@xxxxxxxxxx/
[5] - https://lore.kernel.org/all/65dcf7ab-1299-411f-9cbc-438ae72ff757@xxxxxxxxx/
[6] - https://lore.kernel.org/all/b824f131-3e51-422c-9e98-044b0a2928a6@xxxxxxxxxx/

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         | 194 +++++++++++++++++++++-------------------
 mm/memory.c             |  56 ++++++++----
 mm/mempolicy.c          |   2 +-
 mm/mremap.c             |   2 +-
 mm/page_alloc.c         |   2 +-
 8 files changed, 152 insertions(+), 115 deletions(-)

-- 
2.53.0