[PATCH v2 00/17] mm: Introduce section-based vmemmap optimization for HugeTLB

[Muchun Song]

This series is split out from the earlier, larger series "mm: Generalize
HVO for HugeTLB and device DAX" [1]. While the parent series generalizes
vmemmap optimization across HugeTLB and device DAX, this subset addresses
a single, self-contained step: making the generic sparse-vmemmap code
section-based optimization aware and switching HugeTLB bootmem pages to
this path.

HugeTLB vmemmap optimization currently has its own early boot setup
path. It pre-populates optimized vmemmap mappings before the normal
sparse-vmemmap population code runs, and sparsemem carries
SPARSEMEM_VMEMMAP_PREINIT only to support that special case.

That makes the HugeTLB vmemmap optimization path harder to share with
other users of sparse-vmemmap optimization and leaves a fair amount of
HugeTLB-specific boot-time state in the generic memory initialization
flow.

This series introduces section-based vmemmap optimization support in
the sparse-vmemmap code and switches HugeTLB bootmem pages over to it.
Instead of having HugeTLB pre-populate optimized vmemmap mappings
itself, HugeTLB now records the compound page order in the corresponding
memory sections. The generic sparse-vmemmap population path can then
allocate or reuse shared tail vmemmap pages based on section metadata.

The patches are organized as follows:

  - patches 1-2 prepare sparsemem and vmemmap optimization metadata
  - patches 3-8 teach the common sparse-vmemmap paths to use that state
  - patches 9-10 switch HugeTLB bootmem optimization to the
    section-based path
  - patches 11-17 clean up sparsemem and HugeTLB bootmem code that is no
    longer needed after the conversion

This is intended to be the second smaller step toward the broader HVO
generalization. The device DAX conversion and the wider HVO
consolidation are left for follow-up series.

v2:
- Kept struct mem_section aligned after relaxing lookup constraints
  (suggested by David Laight).
- Folded section order tracking into the first user instead of keeping
  a standalone API-only patch (suggested by Mike Rapoport).
- Renamed the HVO order macros with a VMEMMAP_OPTIMIZATION prefix
  (suggested by Mike Rapoport).
- Moved pfn_to_zone() before the sparse-vmemmap optimization changes
  (suggested by Mike Rapoport).
- Kept vmemmap accounting and population logic in sparse-vmemmap.c
  (suggested by Mike Rapoport).
- Renamed the early sparsemem helper to sparse_sections_init()
  (suggested by Mike Rapoport).
- Fixed the !SPARSEMEM stub name so SPARSEMEM=n builds compile
  (reported by Sashiko).
- Guard section_order() with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP so
  it returns 0 when HVO is disabled and lets the compiler optimize the
  code as much as possible (suggested by Mike Rapoport)
- Collected Acked-by tags from Mike Rapoport.

[1] https://lore.kernel.org/linux-mm/20260513130542.35604-1-songmuchun@xxxxxxxxxxxxx/

Muchun Song (17):
  mm/sparse: relax struct mem_section size constraints
  mm/sparse-vmemmap: rename HVO order macros
  mm/mm_init: skip initializing shared vmemmap tail pages
  mm/sparse-vmemmap: initialize shared tail vmemmap pages on allocation
  mm/sparse-vmemmap: support section-based vmemmap accounting
  mm/mm_init: factor out pfn_to_zone()
  mm/sparse-vmemmap: move vmemmap_get_tail() before PTE population
  mm/sparse-vmemmap: support section-based vmemmap optimization
  mm/sparse: initialize memory sections earlier
  mm/hugetlb: switch HugeTLB to section-based vmemmap optimization
  mm/sparse-vmemmap: remove SPARSEMEM_VMEMMAP_PREINIT support
  mm/sparse: inline usemap allocation into sparse_init_nid()
  mm/sparse: remove section_map_size()
  mm/hugetlb: remove HUGE_BOOTMEM_HVO
  mm/hugetlb: remove HUGE_BOOTMEM_CMA
  mm/hugetlb: localize struct huge_bootmem_page
  mm/hugetlb: localize HUGE_BOOTMEM_ZONES_VALID

 arch/x86/Kconfig        |   1 -
 fs/Kconfig              |   1 -
 include/linux/hugetlb.h |   5 --
 include/linux/mm.h      |   4 -
 include/linux/mmzone.h  |  72 +++++++---------
 mm/Kconfig              |   5 --
 mm/hugetlb.c            |  64 ++++-----------
 mm/hugetlb_vmemmap.c    | 103 +----------------------
 mm/hugetlb_vmemmap.h    |  13 +--
 mm/internal.h           |   7 --
 mm/mm_init.c            |  62 ++++++++------
 mm/mm_init.h            |   1 +
 mm/sparse-vmemmap.c     | 176 +++++++++++++++++-----------------------
 mm/sparse.c             |  94 ++++-----------------
 mm/sparse.h             |  67 +++++++++++++++
 scripts/gdb/linux/mm.py |   6 +-
 16 files changed, 253 insertions(+), 428 deletions(-)


base-commit: 0718283ab28bc3907e10b61a6b4be6fefa1cbb2f
-- 
2.54.0