Commit e66f0972 authored Sep 11, 2013 by Joonsoo Kim Committed by Linus Torvalds Sep 11, 2013

mm, page_alloc: add unlikely macro to help compiler optimization



We rarely allocate a page with ALLOC_NO_WATERMARKS and it is used in slow
path.  For helping compiler optimization, add unlikely macro to
ALLOC_NO_WATERMARKS checking.

This patch doesn't have any effect now, because gcc already optimize this
properly.  But we cannot assume that gcc always does right and nobody
re-evaluate if gcc do proper optimization with their change, for example,
it is not optimized properly on v3.10.  So adding compiler hint here is
reasonable.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1da6f0e1

mm/page_alloc.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1909,7 +1909,7 @@ zonelist_scan:
		!cpuset_zone_allowed_softwall(zone, gfp_mask))
		continue;
		BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
		if (alloc_flags & ALLOC_NO_WATERMARKS)
		if (unlikely(alloc_flags & ALLOC_NO_WATERMARKS))
		goto try_this_zone;
		/*
		* Distribute pages in proportion to the individual

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