From e57b9d8c5ad08ed8cbca7e51fe252719a2845394 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 22 Feb 2017 15:44:47 -0800 Subject: [PATCH] mm/mmzone.c: swap likely to unlikely as code logic is different for next_zones_zonelist() Commit 682a3385e773 ("mm, page_alloc: inline the fast path of the zonelist iterator") changed how next_zones_zonelist() is called, by adding a static inline function to do the fast path. This function adds: if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx)) return z; return __next_zones_zonelist(z, highest_zoneidx, nodes); Where __next_zones_zonelist() is only called when nodes is not NULL or zonelist_zone_idx(z) is less than highest_zoneidx. The original next_zone_zonelist() was converted to __next_zones_zonelist() but it still maintained: if (likely(nodes == NULL)) Which is now actually a very unlikely, as it is only called with nodes equal to NULL when zonelist_zone_idx(z) is greater than highest_zoneidx. Before this commit, this if had this statistic: correct incorrect % Function File Line ------- --------- - -------- ---- ---- 837895 446078 34 next_zones_zonelist mmzone.c 63 After this commit, it has: correct incorrect % Function File Line ------- --------- - -------- ---- ---- 10 173840 99 __next_zones_zonelist mmzone.c 63 Thus, the if statement is now much more unlikely than it ever was as a likely. Link: http://lkml.kernel.org/r/20170105200102.77989567@gandalf.local.home Signed-off-by: Steven Rostedt (VMware) Acked-by: Mel Gorman Acked-by: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mmzone.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mmzone.c b/mm/mmzone.c index 5652be858e5e..a51c0a67ea3d 100644 --- a/mm/mmzone.c +++ b/mm/mmzone.c @@ -60,7 +60,7 @@ struct zoneref *__next_zones_zonelist(struct zoneref *z, * Find the next suitable zone to use for the allocation. * Only filter based on nodemask if it's set */ - if (likely(nodes == NULL)) + if (unlikely(nodes == NULL)) while (zonelist_zone_idx(z) > highest_zoneidx) z++; else