[PATCH v5 0/6] mm: fix vmemmap optimization accounting and initialization

Muchun Song
2026-04-23T07:19:21Z

The series fixes several bugs in vmemmap optimization, mainly around
incorrect page accounting and memmap initialization in DAX and memory
hotplug paths. It also fixes pageblock migratetype initialization and
struct page initialization for ZONE_DEVICE compound pages.

The first four patches fix vmemmap accounting issues. The first patch
fixes an accounting underflow in the section activation failure path.
The second patch fixes incorrect altmap passing in the error path.
The third patch passes pgmap through memory deactivation paths so the
teardown side can determine whether vmemmap optimization was in effect.
The fourth patch uses that information to account the optimized DAX
vmemmap size correctly.

The last two patches fix initialization issues in mm/mm_init. One makes
sure all pageblocks in ZONE_DEVICE compound pages get their migratetype
initialized. The other fixes a case where DAX memory hotplug reuses an
unoptimized early-section memmap while compound_nr_pages() still assumes
vmemmap optimization, leaving tail struct pages uninitialized.

Changelog:
v4 -> v5:
- mm/memory_hotplug: Fix incorrect altmap passing in error path (new bugfix
suggested by Sashiko).
- mm/sparse-vmemmap: Rename section_vmemmap_pages() to
section_nr_vmemmap_pages() and use two-tab indent (suggested by David).
- mm/sparse-vmemmap: Use 1UL for pages_per_compound and use const for
order and pages_per_compound (suggested by David).
- mm/sparse-vmemmap: Simplify VM_WARN_ON_ONCE checks for better readability
(suggested by David).
- mm/mm_init: Use two-tab indent and const for @end in
pageblock_migratetype_init_range() (suggested by David).
- Collect Acked-by tags from David.

Muchun Song (6):
mm/sparse-vmemmap: Fix vmemmap accounting underflow
mm/memory_hotplug: Fix incorrect altmap passing in error path
mm/sparse-vmemmap: Pass @pgmap argument to memory deactivation paths
mm/sparse-vmemmap: Fix DAX vmemmap accounting with optimization
mm/mm_init: Fix pageblock migratetype for ZONE_DEVICE compound pages
mm/mm_init: Fix uninitialized struct pages for ZONE_DEVICE

arch/arm64/mm/mmu.c | 5 +--
arch/loongarch/mm/init.c | 5 +--
arch/powerpc/mm/mem.c | 5 +--
arch/riscv/mm/init.c | 5 +--
arch/s390/mm/init.c | 5 +--
arch/x86/mm/init_64.c | 5 +--
include/linux/memory_hotplug.h | 6 +--
mm/memory_hotplug.c | 15 ++++----
mm/memremap.c | 4 +-
mm/mm_init.c | 34 +++++++++-------
mm/sparse-vmemmap.c | 37 ++++++++++++++----
11 files changed, 81 insertions(+), 45 deletions(-)

--
2.20.1