Re: [PATCH 00/49] mm: Generalize vmemmap optimization for DAX and HugeTLB

Muchun Song
2026-04-15T11:22:58Z

> On Apr 5, 2026, at 20:51, Muchun Song <songmuchun@bytedance.com> wrote:
>
> Overview:
> This patch series generalizes the HugeTLB Vmemmap Optimization (HVO)
> into a generic vmemmap optimization framework that can be used by both
> HugeTLB and DAX.
>
> Background:
> Currently, the vmemmap optimization feature is highly coupled with
> HugeTLB. However, DAX also has similar requirements for optimizing vmemmap
> pages to save memory. The current implementation has separate vmemmap
> optimization paths for HugeTLB and DAX, leading to duplicated logic,
> complex initialization sequences, and architecture-specific flags.
>
> Implementation:
> This series breaks down the optimization into a generic framework:
> - Patch 1-6: Fix bugs related to sparse vmemmap initialization and DAX.
> - Patch 7-13: Refactor the existing sparse vmemmap initialization.
> - Patch 14-26: Decouple the vmemmap optimization from HugeTLB and
> introduce generic optimization macros and functions.
> - Patch 27-39: Switch HugeTLB and DAX to use the generic framework.
> - Patch 40-49: Clean up the old HVO-specific code and simplify it.
>
> Benifit:
> - When CONFIG_DEFERRED_STRUCT_PAGE_INIT is disabled, all struct pages
> utilizing HVO (HugeTLB Vmemmap Optimization) skip initialization in
> memmap_init, significantly accelerating boot times.
> - All architectures supporting HVO benefit from the optimizations
> provided by SPARSEMEM_VMEMMAP_PREINIT without requiring
> architecture-specific adaptations.
> - Device DAX struct page savings are further improved, saving an
> additional 4KB of struct page memory for every 2MB huge page.
> - Vmemmap tail pages used for Device DAX shared mappings are changed
> from read-write to read-only, enhancing system security.
> - HugeTLB and Device DAX now share a unified vmemmap optimization
> framework, reducing long-term maintenance overhead.
>
> Testing:
> - Verification: Compiled and tested on x86 architecture.

Hi all,

I have factored out all the bug fixes from this patchset into a new,
dedicated series:

https://lore.kernel.org/linux-mm/20260415111412.1003526-1-songmuchun@bytedance.com/T/#t

Once those fixes are merged, I will follow up with v2 of this series.
Thanks for your patience and feedback!

Thanks,
Muchun

>
>
> Chengkaitao (1):
> mm: Convert vmemmap_p?d_populate() to static functions
>
> Muchun Song (48):
> mm/sparse: fix vmemmap accounting imbalance on memory hotplug error
> mm/sparse: add a @pgmap argument to memory deactivation paths
> mm/sparse: fix vmemmap page accounting for HVOed DAX
> mm/sparse: add a @pgmap parameter to arch vmemmap_populate()
> mm/sparse: fix missing architecture-specific page table sync for HVO
> DAX
> mm/mm_init: fix uninitialized pageblock migratetype for ZONE_DEVICE
> compound pages
> mm/mm_init: use pageblock_migratetype_init_range() in
> deferred_free_pages()
> mm: panic on memory allocation failure in sparse_init_nid()
> mm: move subsection_map_init() into sparse_init()
> mm: defer sparse_init() until after zone initialization
> mm: make set_pageblock_order() static
> mm: integrate sparse_vmemmap_init_nid_late() into sparse_init_nid()
> mm/cma: validate hugetlb CMA range by zone at reserve time
> mm/hugetlb: free cross-zone bootmem gigantic pages after allocation
> mm/hugetlb: initialize vmemmap optimization in early stage
> mm: remove sparse_vmemmap_init_nid_late()
> mm/mm_init: make __init_page_from_nid() static
> mm/sparse-vmemmap: remove the VMEMMAP_POPULATE_PAGEREF flag
> mm: rename vmemmap optimization macros to generic names
> mm/sparse: drop power-of-2 size requirement for struct mem_section
> mm/sparse: introduce compound page order to mem_section
> mm/mm_init: skip initializing shared tail pages for compound pages
> mm/sparse-vmemmap: initialize shared tail vmemmap page upon allocation
> mm/sparse-vmemmap: support vmemmap-optimizable compound page
> population
> mm/hugetlb: use generic vmemmap optimization macros
> mm: call memblocks_present() before HugeTLB initialization
> mm/hugetlb: switch HugeTLB to use generic vmemmap optimization
> mm: extract pfn_to_zone() helper
> mm/sparse-vmemmap: remove unused SPARSEMEM_VMEMMAP_PREINIT feature
> mm/hugetlb: remove HUGE_BOOTMEM_HVO flag and simplify pre-HVO logic
> mm/sparse-vmemmap: consolidate shared tail page allocation
> mm: introduce CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
> mm/sparse-vmemmap: switch DAX to use generic vmemmap optimization
> mm/sparse-vmemmap: introduce section zone to struct mem_section
> powerpc/mm: use generic vmemmap_shared_tail_page() in compound vmemmap
> mm/sparse-vmemmap: unify DAX and HugeTLB vmemmap optimization
> mm/sparse-vmemmap: remap the shared tail pages as read-only
> mm/sparse-vmemmap: remove unused ptpfn argument
> mm/hugetlb_vmemmap: remove vmemmap_wrprotect_hvo() and related code
> mm/sparse: simplify section_vmemmap_pages()
> mm/sparse-vmemmap: introduce section_vmemmap_page_structs()
> powerpc/mm: rely on generic vmemmap_can_optimize() to simplify code
> mm/sparse-vmemmap: drop ARCH_WANT_OPTIMIZE_DAX_VMEMMAP and simplify
> checks
> mm/sparse-vmemmap: drop @pgmap parameter from vmemmap populate APIs
> mm/sparse: replace pgmap with order and zone in sparse_add_section()
> mm: redefine HVO as Hugepage Vmemmap Optimization
> Documentation/mm: restructure vmemmap_dedup.rst to reflect generalized
> HVO
> mm: consolidate struct page power-of-2 size checks for HVO
>
> .../admin-guide/kernel-parameters.txt | 2 +-
> Documentation/admin-guide/sysctl/vm.rst | 2 +-
> Documentation/mm/vmemmap_dedup.rst | 218 ++--------
> arch/powerpc/Kconfig | 1 -
> arch/powerpc/include/asm/book3s/64/radix.h | 12 -
> arch/powerpc/mm/book3s64/radix_pgtable.c | 114 +----
> arch/powerpc/mm/init_64.c | 1 +
> arch/riscv/Kconfig | 1 -
> arch/x86/Kconfig | 2 -
> fs/Kconfig | 6 +-
> include/linux/hugetlb.h | 7 +-
> include/linux/memory_hotplug.h | 2 +-
> include/linux/mm.h | 50 +--
> include/linux/mm_types.h | 2 +
> include/linux/mm_types_task.h | 4 +
> include/linux/mmzone.h | 143 ++++---
> include/linux/page-flags.h | 31 +-
> kernel/bounds.c | 2 +
> mm/Kconfig | 20 +-
> mm/bootmem_info.c | 5 +-
> mm/cma.c | 3 +-
> mm/hugetlb.c | 143 +++----
> mm/hugetlb_cma.c | 3 +-
> mm/hugetlb_vmemmap.c | 237 +----------
> mm/hugetlb_vmemmap.h | 35 +-
> mm/internal.h | 26 +-
> mm/memory_hotplug.c | 15 +-
> mm/mm_init.c | 138 +++---
> mm/sparse-vmemmap.c | 392 +++++-------------
> mm/sparse.c | 85 ++--
> mm/util.c | 2 +-
> scripts/gdb/linux/mm.py | 6 +-
> 32 files changed, 513 insertions(+), 1197 deletions(-)
>
> --
> 2.20.1
>