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

[Mike Rapoport]

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@xxxxxxxxxx>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>

> ---
>  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
> 

-- 
Sincerely yours,
Mike.