Re: [PATCH 10/49] mm: move subsection_map_init() into sparse_init()

Mike Rapoport
2026-04-28T07:06:39Z

On Sun, Apr 05, 2026 at 08:52:01PM +0800, Muchun Song wrote:
> Move the initialization of the subsection map from free_area_init()
> into sparse_init(). This encapsulates the logic within the sparse
> memory initialization code.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
> mm/internal.h | 5 ++---
> mm/mm_init.c | 10 ++--------
> mm/sparse-vmemmap.c | 11 ++++++++++-
> mm/sparse.c | 1 +
> 4 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index edb1c04d0617..d70075d0e788 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1004,10 +1004,9 @@ static inline void sparse_init(void) {}
> * mm/sparse-vmemmap.c
> */
> #ifdef CONFIG_SPARSEMEM_VMEMMAP
> -void sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages);
> +void sparse_init_subsection_map(void);
> #else
> -static inline void sparse_init_subsection_map(unsigned long pfn,
> - unsigned long nr_pages)
> +static inline void sparse_init_subsection_map(void)
> {
> }
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */

I side note: we might want to split out mm/sparse.h and also move some
declarations from include/linux/mmzone.h there.

> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index a92c5053f63d..5ca4503e7622 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1857,18 +1857,12 @@ static void __init free_area_init(void)
> (u64)zone_movable_pfn[i] << PAGE_SHIFT);
> }
>
> - /*
> - * Print out the early node map, and initialize the
> - * subsection-map relative to active online memory ranges to
> - * enable future "sub-section" extensions of the memory map.
> - */
> + /* Print out the early node map. */
> pr_info("Early memory node ranges\n");
> - for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
> + for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid)
> pr_info(" node %3d: [mem %#018Lx-%#018Lx]\n", nid,
> (u64)start_pfn << PAGE_SHIFT,
> ((u64)end_pfn << PAGE_SHIFT) - 1);
> - sparse_init_subsection_map(start_pfn, end_pfn - start_pfn);
> - }
>
> /* Initialise every node */
> mminit_verify_pageflags_layout();
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 0ee03db0b22f..b7201c235419 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -603,7 +603,7 @@ static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> bitmap_set(map, idx, end - idx + 1);
> }
>
> -void __init sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +static void __init sparse_init_subsection_map_range(unsigned long pfn, unsigned long nr_pages)
> {
> int end_sec_nr = pfn_to_section_nr(pfn + nr_pages - 1);
> unsigned long nr, start_sec_nr = pfn_to_section_nr(pfn);
> @@ -626,6 +626,15 @@ void __init sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages
> }
> }
>
> +void __init sparse_init_subsection_map(void)
> +{
> + int i, nid;
> + unsigned long start, end;
> +
> + for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid)
> + sparse_init_subsection_map_range(start, end - start);
> +}
> +
> #ifdef CONFIG_MEMORY_HOTPLUG
>
> /* Mark all memory sections within the pfn range as online */
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 5c12b979a618..c7f91dc2e5b5 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -424,5 +424,6 @@ void __init sparse_init(void)
> }
> /* cover the last node */
> sparse_init_nid(nid_begin, pnum_begin, pnum_end, map_count);
> + sparse_init_subsection_map();
> vmemmap_populate_print_last();
> }
> --
> 2.20.1
>

--
Sincerely yours,
Mike.