Re: [PATCH v2] mm/sparse.c: Use kvmalloc_node/kvfree to alloc/free memmap for the classic sparse

[Matthew Wilcox]

On Thu, Mar 12, 2020 at 09:08:22PM +0800, Baoquan He wrote:
> This change makes populate_section_memmap()/depopulate_section_memmap
> much simpler.
> 
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
> v1->v2:
>   The old version only used __get_free_pages() to replace alloc_pages()
>   in populate_section_memmap().
>   http://lkml.kernel.org/r/20200307084229.28251-8-bhe@xxxxxxxxxx
> 
>  mm/sparse.c | 27 +++------------------------
>  1 file changed, 3 insertions(+), 24 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index bf6c00a28045..362018e82e22 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -734,35 +734,14 @@ static void free_map_bootmem(struct page *memmap)
>  struct page * __meminit populate_section_memmap(unsigned long pfn,
>  		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
>  {
> -	struct page *page, *ret;
> -	unsigned long memmap_size = sizeof(struct page) * PAGES_PER_SECTION;
> -
> -	page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size));
> -	if (page)
> -		goto got_map_page;
> -
> -	ret = vmalloc(memmap_size);
> -	if (ret)
> -		goto got_map_ptr;
> -
> -	return NULL;
> -got_map_page:
> -	ret = (struct page *)pfn_to_kaddr(page_to_pfn(page));
> -got_map_ptr:
> -
> -	return ret;
> +	return kvmalloc_node(sizeof(struct page) * PAGES_PER_SECTION,
> +			     GFP_KERNEL|__GFP_NOWARN, nid);

Use of NOWARN here is inappropriate, because there's no fallback.
Also, I'd use array_size(sizeof(struct page), PAGES_PER_SECTION).