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) <rostedt@goodmis.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmzone.c b/mm/mmzone.c
index 5652be858e5e320c7a748d4e6a407c66baaa62a0..a51c0a67ea3d3725369c88a23340d2fc745e0e62 100644 (file)
--- 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