linux-kernel - [PATCH 1/4] mm, page_alloc: Only check PageCompound for high-order pages -fix

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Date:	Wed, 27 Apr 2016 13:24:42 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 1/4] mm, page_alloc: Only check PageCompound for high-order pages -fix

Vlastimil Babka pointed out that an unlikely annotation in free_pages_prepare
shrinks stack usage by moving compound handling to the end of the function.

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-30 (-30)
function                                     old     new   delta
free_pages_prepare                           771     741     -30

It's also consistent with the buffered_rmqueue path.

This is a fix to the mmotm patch
mm-page_alloc-only-check-pagecompound-for-high-order-pages.patch.

Suggested-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1da56779f8fa..d8383750bd43 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1003,7 +1003,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 	 * Check tail pages before head page information is cleared to
 	 * avoid checking PageCompound for order-0 pages.
 	 */
-	if (order) {
+	if (unlikely(order)) {
 		bool compound = PageCompound(page);
 		int i;
 
-- 
2.6.4