Re: [PATCH 08/14] mm/sparse: remove sparse_decode_mem_map()

Lorenzo Stoakes (Oracle)
2026-03-17T19:25:54Z

On Tue, Mar 17, 2026 at 05:56:46PM +0100, David Hildenbrand (Arm) wrote:
> section_deactivate() applies to CONFIG_SPARSEMEM_VMEMMAP only. So we can
> just use pfn_to_page() (after making sure we have the start PFN of the
> section), and remove sparse_decode_mem_map().
>
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

it's more like pfn_to_patch(), so that's a:

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

From me!

> ---
> include/linux/memory_hotplug.h | 2 --
> mm/sparse.c | 16 +---------------
> 2 files changed, 1 insertion(+), 17 deletions(-)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index e77ef3d7ff73..815e908c4135 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -308,8 +308,6 @@ extern int sparse_add_section(int nid, unsigned long pfn,
> struct dev_pagemap *pgmap);
> extern void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
> struct vmem_altmap *altmap);
> -extern struct page *sparse_decode_mem_map(unsigned long coded_mem_map,
> - unsigned long pnum);
> extern struct zone *zone_for_pfn_range(enum mmop online_type,
> int nid, struct memory_group *group, unsigned long start_pfn,
> unsigned long nr_pages);
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 636a4a0f1199..2a1f662245bc 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -274,18 +274,6 @@ static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long p
> return coded_mem_map;
> }
>
> -#ifdef CONFIG_MEMORY_HOTPLUG
> -/*
> - * Decode mem_map from the coded memmap
> - */
> -struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pnum)
> -{
> - /* mask off the extra low bits of information */
> - coded_mem_map &= SECTION_MAP_MASK;
> - return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum);
> -}
> -#endif /* CONFIG_MEMORY_HOTPLUG */
> -
> static void __meminit sparse_init_one_section(struct mem_section *ms,
> unsigned long pnum, struct page *mem_map,
> struct mem_section_usage *usage, unsigned long flags)
> @@ -758,8 +746,6 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>
> empty = is_subsection_map_empty(ms);
> if (empty) {
> - unsigned long section_nr = pfn_to_section_nr(pfn);
> -
> /*
> * Mark the section invalid so that valid_section()
> * return false. This prevents code from dereferencing
> @@ -778,7 +764,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> kfree_rcu(ms->usage, rcu);
> WRITE_ONCE(ms->usage, NULL);
> }
> - memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> + memmap = pfn_to_page(SECTION_ALIGN_DOWN(pfn));
> }
>
> /*
> --
> 2.43.0
>

Cheers, Lorenzo