Re: [PATCH v4 2/5] mm/sparse-vmemmap: Pass @pgmap argument to memory deactivation paths

David Hildenbrand (Arm)
2026-04-22T18:50:11Z

On 4/22/26 10:14, Muchun Song wrote:
> Currently, the memory hot-remove call chain -- arch_remove_memory(),
> __remove_pages(), sparse_remove_section() and section_deactivate() --
> does not carry the struct dev_pagemap pointer. This prevents the lower
> levels from knowing whether the section was originally populated with
> vmemmap optimizations (e.g., DAX with vmemmap optimization enabled).
>
> Without this information, we cannot call vmemmap_can_optimize() to
> determine if the vmemmap pages were optimized. As a result, the vmemmap
> page accounting during teardown will mistakenly assume a non-optimized
> allocation, leading to incorrect memmap statistics.
>
> To lay the groundwork for fixing the vmemmap page accounting, we need
> to pass the @pgmap pointer down to the deactivation location. Plumb the
> @pgmap argument through the APIs of arch_remove_memory(), __remove_pages()
> and sparse_remove_section(), mirroring the corresponding *_activate()
> paths.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>

[...]

> static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
> - struct vmem_altmap *altmap)
> + struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
> {
> unsigned long start = (unsigned long) pfn_to_page(pfn);
> unsigned long end = start + nr_pages * sizeof(struct page);
> @@ -746,7 +746,7 @@ static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> * usage map, but still need to free the vmemmap range.
> */
> static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> - struct vmem_altmap *altmap)
> + struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
> {
> struct mem_section *ms = __pfn_to_section(pfn);
> bool section_is_early = early_section(ms);
> @@ -784,7 +784,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> * section_activate() and pfn_valid() .
> */
> if (!section_is_early)
> - depopulate_section_memmap(pfn, nr_pages, altmap);
> + depopulate_section_memmap(pfn, nr_pages, altmap, pgmap);
> else if (memmap)
> free_map_bootmem(memmap);
>
> @@ -828,7 +828,7 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
>
> memmap = populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap);
> if (!memmap) {
> - section_deactivate(pfn, nr_pages, altmap);
> + section_deactivate(pfn, nr_pages, altmap, pgmap);
> return ERR_PTR(-ENOMEM);
> }
>
> @@ -889,13 +889,13 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
> }
>
> void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
> - struct vmem_altmap *altmap)
> + struct vmem_altmap *altmap, struct dev_pagemap *pgmap)

While at it, could switch to two-tab indent here as well.

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

--
Cheers,

David