[PATCH v4 0/5] mm: Fix vmemmap optimization accounting and initialization

Muchun Song
2026-04-22T08:14:49Z

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 three patches fix vmemmap accounting issues. The first patch
fixes an accounting underflow in the section activation failure path.
The second patch passes pgmap through memory deactivation paths so the
teardown side can determine whether vmemmap optimization was in effect.
The third 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.

v3 -> v4:
- Collect Acked-by and Reviewed-by tags from Oscar Salvador.
- Fix the build issue reported by Sashiko.
- Add a fix for uninitialized struct pages for ZONE_DEVICE, based on
analysis from Sashiko and verified locally.

Muchun Song (5):
mm/sparse-vmemmap: Fix vmemmap accounting underflow
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 | 58 +++++++++++++++++++++++-----------
mm/sparse-vmemmap.c | 56 ++++++++++++++++++++++++--------
11 files changed, 114 insertions(+), 55 deletions(-)

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2.20.1