Re: [PATCH] mm, page_alloc: cleanup usemap_size() when SPARSEMEM is not set

[Michal Hocko <mhocko@suse.com>]

On Sat 19-01-19 07:49:05, Wei Yang wrote:
> Two cleanups in this patch:
> 
>   * since pageblock_nr_pages == (1 << pageblock_order), the roundup()
>     and right shift pageblock_order could be replaced with
>     DIV_ROUND_UP()

Why is this change worth it?

>   * use BITS_TO_LONGS() to get number of bytes for bitmap
> 
> This patch also fix one typo in comment.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> ---
>  mm/page_alloc.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d295c9bc01a8..d7073cedd087 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6352,7 +6352,7 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
>  /*
>   * Calculate the size of the zone->blockflags rounded to an unsigned long
>   * Start by making sure zonesize is a multiple of pageblock_order by rounding
> - * up. Then use 1 NR_PAGEBLOCK_BITS worth of bits per pageblock, finally
> + * up. Then use 1 NR_PAGEBLOCK_BITS width of bits per pageblock, finally

why do you change this?

>   * round what is now in bits to nearest long in bits, then return it in
>   * bytes.
>   */
> @@ -6361,12 +6361,9 @@ static unsigned long __init usemap_size(unsigned long zone_start_pfn, unsigned l
>  	unsigned long usemapsize;
>  
>  	zonesize += zone_start_pfn & (pageblock_nr_pages-1);
> -	usemapsize = roundup(zonesize, pageblock_nr_pages);
> -	usemapsize = usemapsize >> pageblock_order;
> +	usemapsize = DIV_ROUND_UP(zonesize, pageblock_nr_pages);
>  	usemapsize *= NR_PAGEBLOCK_BITS;
> -	usemapsize = roundup(usemapsize, 8 * sizeof(unsigned long));
> -
> -	return usemapsize / 8;
> +	return BITS_TO_LONGS(usemapsize) * sizeof(unsigned long);
>  }
>  
>  static void __ref setup_usemap(struct pglist_data *pgdat,
> -- 
> 2.15.1
> 

-- 
Michal Hocko
SUSE Labs