Re: free_pages_check

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

On Mon, 7 Jan 2008 18:43:46 -0800 "Yinghai Lu" <yhlu.kernel@gmail.com> wrote:

> wonder why free_pages_check mm/page_alloc.c is using bit OR than logical OR
> 
> @@ -450,9 +450,9 @@ static inline void __free_one_page(struc
> 
>  static inline int free_pages_check(struct page *page)
>  {
> -       if (unlikely(page_mapcount(page) |
> -               (page->mapping != NULL)  |
> -               (page_count(page) != 0)  |
> +       if (unlikely(page_mapcount(page) ||
> +               (page->mapping != NULL)  ||
> +               (page_count(page) != 0)  ||
>                 (page->flags & (
>                         1 << PG_lru     |
>                         1 << PG_private |

It's a hack^Wtrick to avoid the generation of a series of not-taken
branches.  I don't recall anyone verifying that it is actually of any
benefit, but the theory is good.

The lack of a comment, however, is not.