Re: [PATCH next] mm/vmscan: __isolate_lru_page_prepare clean up

[Andrew Morton]

On Fri, 20 Nov 2020 16:03:33 +0800 Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> wrote:

> The function just return 2 results, so use a 'switch' to deal with its
> result is unnecessary, and simplify it to a bool func as Vlastimil
> suggested.
> 
> Also removed 'goto' in using by reusing list_move().
> 
> ...
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1540,7 +1540,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
>   */
>  int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
>  {
> -	int ret = -EBUSY;
> +	int ret = false;
>  
>  	/* Only take pages on the LRU. */
>  	if (!PageLRU(page))
> @@ -1590,7 +1590,7 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
>  	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
>  		return ret;
>  
> -	return 0;
> +	return true;
>  }

The resulting __isolate_lru_page_prepare() is rather unpleasing.

- Why return an int and not a bool?

- `int ret = false' is a big hint that `ret' should have bool type!

- Why not just remove `ret' and do `return false' in all those `return
  ret' places?

- The __isolate_lru_page_prepare() kerneldoc still says "returns 0 on
  success, -ve errno on failure".