[PATCH] mm: Remove unlikely from the current_order test

[PATCH] mm: Remove unlikely from the current_order test

[Zhang Yanfei]

From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

In __rmqueue_fallback(), current_order loops down from MAX_ORDER - 1
to the order passed. MAX_ORDER is typically 11 and pageblock_order
is typically 9 on x86. Integer division truncates, so pageblock_order / 2
is 4.  For the first eight iterations, it's guaranteed that
current_order >= pageblock_order / 2 if it even gets that far!

So just remove the unlikely(), it's completely bogus.

Suggested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
---
 mm/page_alloc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c3edb62..7b4f367 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1050,7 +1050,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
 			 * MIGRATE_CMA areas.
 			 */
 			if (!is_migrate_cma(migratetype) &&
-			    (unlikely(current_order >= pageblock_order / 2) ||
+			    (current_order >= pageblock_order / 2 ||
 			     start_migratetype == MIGRATE_RECLAIMABLE ||
 			     page_group_by_mobility_disabled)) {
 				int pages;
-- 
1.7.1

Re: [PATCH] mm: Remove unlikely from the current_order test

[David Rientjes]

On Tue, 18 Jun 2013, Zhang Yanfei wrote:

> From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
> 
> In __rmqueue_fallback(), current_order loops down from MAX_ORDER - 1
> to the order passed. MAX_ORDER is typically 11 and pageblock_order
> is typically 9 on x86. Integer division truncates, so pageblock_order / 2
> is 4.  For the first eight iterations, it's guaranteed that
> current_order >= pageblock_order / 2 if it even gets that far!
> 
> So just remove the unlikely(), it's completely bogus.
> 
> Suggested-by: David Rientjes <rientjes@google.com>
> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

Acked-by: David Rientjes <rientjes@google.com>