linux-kernel - [PATCH] mm: kill one if in loop of __free_pages

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Date:	Mon, 22 Jul 2013 19:17:42 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>, Mel Gorman <mgorman@...e.de>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Yinghai Lu <yinghai@...nel.org>
Subject: [PATCH] mm: kill one if in loop of __free_pages_bootmem

We should not check loop+1 with loop end in loop body.
Just duplicate two lines code to avoid it.

That will help a bit when we have huge amount of pages on
system with 16TiB memory.

Signed-off-by: Yinghai Lu <yinghai@...nel.org>
Cc: Mel Gorman <mgorman@...e.de>

---
 mm/page_alloc.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c
+++ linux-2.6/mm/page_alloc.c
@@ -750,19 +750,19 @@ static void __free_pages_ok(struct page
 void __init __free_pages_bootmem(struct page *page, unsigned int order)
 {
 	unsigned int nr_pages = 1 << order;
+	struct page *p = page;
 	unsigned int loop;
 
-	prefetchw(page);
-	for (loop = 0; loop < nr_pages; loop++) {
-		struct page *p = &page[loop];
-
-		if (loop + 1 < nr_pages)
-			prefetchw(p + 1);
+	prefetchw(p);
+	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
+		prefetchw(p + 1);
 		__ClearPageReserved(p);
 		set_page_count(p, 0);
 	}
+	__ClearPageReserved(p);
+	set_page_count(p, 0);
 
-	page_zone(page)->managed_pages += 1 << order;
+	page_zone(page)->managed_pages += nr_pages;
 	set_page_refcounted(page);
 	__free_pages(page, order);
 }
--
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