Re: [PATCH] page_alloc: change bit ops 'or' to logical ops in free/new page check

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> Using logical 'or' in  function free_page_mlock() and
> check_new_page() makes code clear and
> sometimes more effective (Because it can ignore other condition
> compare if the first condition
> is already true).
> 
> It's Nick's patch "mm: microopt conditions" changed it from logical
> ops to bit ops.
> Maybe I didn't consider something. If so, please let me know and just
> ignore this patch.
> Thanks!

I think current code is intentional. On modern cpu, bit-or is faster than
logical or.

Do you have opposite benchmark number result?


> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>
> ---
> 
> diff --git mm/page_alloc.c mm/page_alloc.c
> index 05ae4e0..91ece14 100644
> --- mm/page_alloc.c
> +++ mm/page_alloc.c
> @@ -500,9 +500,9 @@ static inline void free_page_mlock(struct page *page)
> 
>  static inline int free_pages_check(struct page *page)
>  {
> -       if (unlikely(page_mapcount(page) |
> -               (page->mapping != NULL)  |
> -               (atomic_read(&page->_count) != 0) |
> +       if (unlikely(page_mapcount(page) ||
> +               (page->mapping != NULL)  ||
> +               (atomic_read(&page->_count) != 0) ||
>                 (page->flags & PAGE_FLAGS_CHECK_AT_FREE))) {
>                 bad_page(page);
>                 return 1;
> @@ -671,9 +671,9 @@ static inline void expand(struct zone *zone, struct page *pa
>   */
>  static inline int check_new_page(struct page *page)
>  {
> -       if (unlikely(page_mapcount(page) |
> -               (page->mapping != NULL)  |
> -               (atomic_read(&page->_count) != 0)  |
> +       if (unlikely(page_mapcount(page) ||
> +               (page->mapping != NULL)  ||
> +               (atomic_read(&page->_count) != 0)  ||
>                 (page->flags & PAGE_FLAGS_CHECK_AT_PREP))) {
>                 bad_page(page);
>                 return 1;
> 
> -- 
> Regards,
> -Bob Liu
> 
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