[PATCH V4 4/4] mm: microoptimize zonelist operations

[Vlastimil Babka]

The function next_zones_zonelist() returns zoneref pointer, as well as zone
pointer via extra parameter. Since the latter can be trivially obtained by
dereferencing the former, the overhead of the extra parameter is unjustified.

This patch thus removes the zone parameter from next_zones_zonelist(). Both
callers happen to be in the same header file, so it's simple to add the
zoneref dereference inline. We save some bytes of code size.

add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-96 (-96)
function                                     old     new   delta
__alloc_pages_nodemask                      2182    2176      -6
nr_free_zone_pages                           129     115     -14
get_page_from_freelist                      2652    2576     -76

add/remove: 0/0 grow/shrink: 1/0 up/down: 10/0 (10)
function                                     old     new   delta
try_to_compact_pages                         569     579     +10

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
---
 include/linux/mmzone.h | 13 +++++++------
 mm/mmzone.c            |  4 +---
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2f0856d..a2884ef 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -970,7 +970,6 @@ static inline int zonelist_node_idx(struct zoneref *zoneref)
  * @z - The cursor used as a starting point for the search
  * @highest_zoneidx - The zone index of the highest zone to return
  * @nodes - An optional nodemask to filter the zonelist with
- * @zone - The first suitable zone found is returned via this parameter
  *
  * This function returns the next zone at or below a given zone index that is
  * within the allowed nodemask using a cursor as the starting point for the
@@ -980,8 +979,7 @@ static inline int zonelist_node_idx(struct zoneref *zoneref)
  */
 struct zoneref *next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes,
-					struct zone **zone);
+					nodemask_t *nodes);
 
 /**
  * first_zones_zonelist - Returns the first zone at or below highest_zoneidx within the allowed nodemask in a zonelist
@@ -1000,8 +998,10 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 					nodemask_t *nodes,
 					struct zone **zone)
 {
-	return next_zones_zonelist(zonelist->_zonerefs, highest_zoneidx, nodes,
-								zone);
+	struct zoneref *z = next_zones_zonelist(zonelist->_zonerefs,
+							highest_zoneidx, nodes);
+	*zone = zonelist_zone(z);
+	return z;
 }
 
 /**
@@ -1018,7 +1018,8 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 #define for_each_zone_zonelist_nodemask(zone, z, zlist, highidx, nodemask) \
 	for (z = first_zones_zonelist(zlist, highidx, nodemask, &zone);	\
 		zone;							\
-		z = next_zones_zonelist(++z, highidx, nodemask, &zone))	\
+		z = next_zones_zonelist(++z, highidx, nodemask),	\
+			zone = zonelist_zone(z))			\
 
 /**
  * for_each_zone_zonelist - helper macro to iterate over valid zones in a zonelist at or below a given zone index
diff --git a/mm/mmzone.c b/mm/mmzone.c
index bf34fb8..7d87ebb 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -54,8 +54,7 @@ static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
 /* Returns the next zone at or below highest_zoneidx in a zonelist */
 struct zoneref *next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes,
-					struct zone **zone)
+					nodemask_t *nodes)
 {
 	/*
 	 * Find the next suitable zone to use for the allocation.
@@ -69,7 +68,6 @@ struct zoneref *next_zones_zonelist(struct zoneref *z,
 				(z->zone && !zref_in_nodemask(z, nodes)))
 			z++;
 
-	*zone = zonelist_zone(z);
 	return z;
 }
 
-- 
2.1.2

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