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Re: [Xen-devel] [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core
- To: Arun KS <arunks@xxxxxxxxxxxxxx>, kys@xxxxxxxxxxxxx, haiyangz@xxxxxxxxxxxxx, sthemmin@xxxxxxxxxxxxx, boris.ostrovsky@xxxxxxxxxx, jgross@xxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, dan.j.williams@xxxxxxxxx, mhocko@xxxxxxxx, iamjoonsoo.kim@xxxxxxx, gregkh@xxxxxxxxxxxxxxxxxxx, osalvador@xxxxxxx, malat@xxxxxxxxxx, kirill.shutemov@xxxxxxxxxxxxxxx, jrdr.linux@xxxxxxxxx, yasu.isimatu@xxxxxxxxx, mgorman@xxxxxxxxxxxxxxxxxxx, aaron.lu@xxxxxxxxx, devel@xxxxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Vlastimil Babka <vbabka@xxxxxxx>
- Date: Wed, 10 Oct 2018 18:36:52 +0200
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- Cc: vinmenon@xxxxxxxxxxxxxx, vatsa@xxxxxxxxxxxxxx, getarunks@xxxxxxxxx
- Delivery-date: Wed, 10 Oct 2018 16:39:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 10/5/18 10:10 AM, 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.
>
> Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Arun KS <arunks@xxxxxxxxxxxxxx>
Yeah, a tight loop with fixed stride is a trivial case for hw prefetcher.
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> 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);
>
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