Re: [Xen-devel] [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core

[Michal Hocko <mhocko@xxxxxxxxxx>]

On Fri 05-10-18 13:40:06, Arun KS wrote:
> They not only increase the code footprint, they actually make things
> slower rather than faster. Remove them as contemporary hardware doesn't
> need any hint.

I agree with the change but it is much better to add some numbers
whenever arguing about performance impact.

> 
> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
> ---
>  mm/page_alloc.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7ab5274..90db431 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1258,14 +1258,10 @@ void __free_pages_core(struct page *page, unsigned 
> int order)
>       struct page *p = page;
>       unsigned int loop;
>  
> -     prefetchw(p);
> -     for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> -             prefetchw(p + 1);
> +     for (loop = 0; loop < nr_pages ; loop++, p++) {
>               __ClearPageReserved(p);
>               set_page_count(p, 0);
>       }
> -     __ClearPageReserved(p);
> -     set_page_count(p, 0);
>  
>       page_zone(page)->managed_pages += nr_pages;
>       set_page_refcounted(page);
> -- 
> 1.9.1
> 

-- 
Michal Hocko
SUSE Labs

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