[dm-devel] [PATCH 2/4] mm/swap: use SECTORS_PER_PAGE_SHIFT to clean up code

[Matthew Wilcox]

On Tue, May 05, 2020 at 07:55:41PM +0800, Zhen Lei wrote:
> +++ b/mm/swapfile.c
> @@ -177,8 +177,8 @@ static int discard_swap(struct swap_info_struct *si)
>  
>  	/* Do not discard the swap header page! */
>  	se = first_se(si);
> -	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
> -	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
> +	start_block = (se->start_block + 1) << SECTORS_PER_PAGE_SHIFT;
> +	nr_blocks = ((sector_t)se->nr_pages - 1) << SECTORS_PER_PAGE_SHIFT;

Thinking about this some more, wouldn't this look better?

	start_block = page_sectors(se->start_block + 1);
	nr_block = page_sectors(se->nr_pages - 1);