linux-kernel - [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages

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Date:   Fri,  5 Oct 2018 13:40:06 +0530
From:   Arun KS <arunks@...eaurora.org>
To:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        akpm@...ux-foundation.org, dan.j.williams@...el.com,
        mhocko@...e.com, vbabka@...e.cz, iamjoonsoo.kim@....com,
        gregkh@...uxfoundation.org, osalvador@...e.de, malat@...ian.org,
        kirill.shutemov@...ux.intel.com, jrdr.linux@...il.com,
        yasu.isimatu@...il.com, mgorman@...hsingularity.net,
        aaron.lu@...el.com, devel@...uxdriverproject.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        xen-devel@...ts.xenproject.org
Cc:     vatsa@...eaurora.org, vinmenon@...eaurora.org, getarunks@...il.com,
        Arun KS <arunks@...eaurora.org>
Subject: [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core

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@...el.com>
Signed-off-by: Arun KS <arunks@...eaurora.org>
---
 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