[PATCH mm-unstable v4 0/5] mm: khugepaged cleanups and mTHP prerequisites

[Nico Pache <npache@redhat.com>]

MAINTAINER NOTE: This is based on mm-unstable with the coresponding
patches reverted then reapplied.

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

V4 Changes:
 - added RB and SB tags
 - Patch1: commit message cleanup/additions
 - Patch1: constify two variables, and change 1<<order to 1L<<..
 - Patch1: change zero-page read path to use update_mmu_cache varient
 - Patch5: remove dead code switch statement (SCAN_PTE_MAPPED_HUGEPAGE)
 - Patch5: remove local mmap_locked from madvise_collapse()
 - Patch5: rename mmap_locked to lock_dropped in ..scan_mm_slot() and
   invert the logic. the madvise|khugepaged code now share the same 
   naming convention across both functions.
 - Patch5: add assertion to collapse_single_pmd() so both madvise_collapse
   and khugepaged assert the lock.
 - Patch5: Convert one of the VM_BUG_ON's to VM_WARN_ON

V3 - https://lore.kernel.org/all/20260311211315.450947-1-npache@redhat.com
V2 - https://lore.kernel.org/all/20260226012929.169479-1-npache@redhat.com
V1 - https://lore.kernel.org/all/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/all/7334b702-f6a0-4ccf-8ac6-8426a90d1846@kernel.org/
[3] - https://lore.kernel.org/all/25723c0f-c702-44ad-93e9-1056313680cd@kernel.org/
[4] - https://lore.kernel.org/all/81ff9caa-50f2-4951-8d82-2c8dcdf3db91@kernel.org/

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         | 207 ++++++++++++++++++++--------------------
 mm/memory.c             |  63 ++++++++----
 mm/mempolicy.c          |   2 +-
 mm/mremap.c             |   2 +-
 mm/page_alloc.c         |   4 +-
 mm/shmem.c              |   3 +-
 9 files changed, 161 insertions(+), 131 deletions(-)

-- 
2.53.0