[PATCH v8 0/6] mm: Fix vmemmap optimization accounting and initialization

Muchun Song
2026-04-28T08:19:13Z

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.

Patches 1-4 fix vmemmap accounting issues. Patch 1 fixes an accounting
underflow in the section activation failure path by moving vmemmap page
accounting into the lower-level allocation and freeing helpers. Patch 2
fixes incorrect altmap passing in the memory hotplug error path. Patch 3
passes pgmap through memory deactivation paths so the teardown side can
determine whether vmemmap optimization was in effect. Patch 4 uses that
information to account the optimized DAX vmemmap size correctly.

Patches 5-6 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.

Changes in v8:
- In patch 4, move VM_WARN_ON_ONCE(nr_pages > PAGES_PER_SECTION) to the
top of section_nr_vmemmap_pages().
- In patch 4, add Acked-by from David Hildenbrand.

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 | 8 +++--
mm/memory_hotplug.c | 13 ++++----
mm/memremap.c | 4 +--
mm/mm_init.c | 47 ++++++++++++++++-----------
mm/sparse-vmemmap.c | 58 ++++++++++++++++++++++++++--------
11 files changed, 105 insertions(+), 55 deletions(-)

base-commit: 39704f00f747aba3144289870b5fd8ac230a9aaf
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2.20.1