Re: [PATCH v2 08/26] swap: Convert add_to_swap() to take a folio

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

On Wed,  4 May 2022 19:28:39 +0100 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:

> The only caller already has a folio available, so this saves a conversion.
> Also convert the return type to boolean.
> 
> ...
>
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -449,7 +449,7 @@ static inline unsigned long total_swapcache_pages(void)
>  }
>  
>  extern void show_swap_cache_info(void);
> -extern int add_to_swap(struct page *page);
> +bool add_to_swap(struct folio *folio);
>  extern void *get_shadow_from_swap_cache(swp_entry_t entry);
>  extern int add_to_swap_cache(struct page *page, swp_entry_t entry,
>  			gfp_t gfp, void **shadowp);
> @@ -630,9 +630,9 @@ struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
>  	return find_get_page(mapping, index);
>  }
>  
> -static inline int add_to_swap(struct page *page)
> +static inline bool add_to_swap(struct folio *folio)
>  {
> -	return 0;
> +	return false;
>  }
>  

Neil's "mm: create new mm/swap.h header file" moved this to mm/swap.h. 
Simple enough.

But mm/swap.h now gets its first mention of a folio yet it includes no
prerequisites.  I guess the includer is responsible for including the
correct headers first, which is pretty sad,

My fingers are itching to add a forward declaration `struct folio;',
but I assume that isn't needed.  We'll find out soon enough ;)