Re: [PATCH 3/4] mm: introduce memmap_alloc() to unify memory map allocation

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 14 Jul 2021 15:37:38 +0300 Mike Rapoport <rppt@kernel.org> wrote:

> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> There are several places that allocate memory for the memory map:
> alloc_node_mem_map() for FLATMEM, sparse_buffer_init() and
> __populate_section_memmap() for SPARSEMEM.
> 
> The memory allocated in the FLATMEM case is zeroed and it is never
> poisoned, regardless of CONFIG_PAGE_POISON setting.
> 
> The memory allocated in the SPARSEMEM cases is not zeroed and it is
> implicitly poisoned inside memblock if CONFIG_PAGE_POISON is set.
> 
> Introduce memmap_alloc() wrapper for memblock allocators that will be used
> for both FLATMEM and SPARSEMEM cases and will makei memory map zeroing and
> poisoning consistent for different memory models.
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6730,6 +6730,26 @@ static void __init memmap_init(void)
>  		init_unavailable_range(hole_pfn, end_pfn, zone_id, nid);
>  }
>  
> +void __init *memmap_alloc(phys_addr_t size, phys_addr_t align,
> +			  phys_addr_t min_addr, int nid, bool exact_nid)
> +{
> +	void *ptr;
> +
> +	if (exact_nid)
> +		ptr = memblock_alloc_exact_nid_raw(size, align, min_addr,
> +						   MEMBLOCK_ALLOC_ACCESSIBLE,
> +						   nid);
> +	else
> +		ptr = memblock_alloc_try_nid_raw(size, align, min_addr,
> +						 MEMBLOCK_ALLOC_ACCESSIBLE,
> +						 nid);
> +
> +	if (ptr && size > 0)
> +		page_init_poison(ptr, size);
> +
> +	return ptr;
> +}
> +
>  static int zone_batchsize(struct zone *zone)
>  {
>  #ifdef CONFIG_MMU
> @@ -7501,8 +7521,8 @@ static void __ref alloc_node_mem_map(struct pglist_data *pgdat)
>  		end = pgdat_end_pfn(pgdat);
>  		end = ALIGN(end, MAX_ORDER_NR_PAGES);
>  		size =  (end - start) * sizeof(struct page);
> -		map = memblock_alloc_node(size, SMP_CACHE_BYTES,
> -					  pgdat->node_id);
> +		map = memmap_alloc(size, SMP_CACHE_BYTES, MEMBLOCK_LOW_LIMIT,
> +				   pgdat->node_id, false);

Mostly offtopic, but...  Why is alloc_node_mem_map() marked __ref? 
afaict it can be __init?