From: Steven Rostedt <rostedt@xxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxx
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmzone.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/mmzone.c~mm-page_alloc-swap-likely-to-unlikely-as-code-logic-is-different-for-next_zones_zonelist mm/mmzone.c
--- a/mm/mmzone.c~mm-page_alloc-swap-likely-to-unlikely-as-code-logic-is-different-for-next_zones_zonelist
+++ a/mm/mmzone.c
@@ -60,7 +60,7 @@ struct zoneref *__next_zones_zonelist(st
* 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
_
--
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