Re: [PATCH v2 06/10] mm/swap: use npage_to_sectors() and PAGE_SECTORS to clean up code

[Matthew Wilcox]

On Thu, May 07, 2020 at 03:50:56PM +0800, Zhen Lei wrote:
> @@ -266,7 +266,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
>  
>  static sector_t swap_page_sector(struct page *page)
>  {
> -	return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
> +	return npage_to_sectors((sector_t)__page_file_index(page));

If you make npage_to_sectors() a proper function instead of a macro,
you can do the casting inside the function instead of in the callers
(which is prone to bugs).

Also, this is a great example of why page_to_sector() was a better name
than npage_to_sectors().  This function doesn't return a count of sectors,
it returns a sector number within the swap device.