[PATCH v2 2/5] mm: Extends local cpu counter vm_diff_nodestat from s8 to s16

[Kemi Wang]

The type s8 used for vm_diff_nodestat[] as local cpu counters has the
limitation of global counters update frequency, especially for those
monotone increasing type of counters like NUMA counters with more and more
cpus/nodes. This patch extends the type of vm_diff_nodestat from s8 to s16
without any functionality change.

                                 before     after
sizeof(struct per_cpu_nodestat)    28         68

Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx>
---
 include/linux/mmzone.h |  4 ++--
 mm/vmstat.c            | 16 ++++++++--------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index c06d880..2da6b6f 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -289,8 +289,8 @@ struct per_cpu_pageset {
 };
 
 struct per_cpu_nodestat {
-	s8 stat_threshold;
-	s8 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
+	s16 stat_threshold;
+	s16 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
 };
 
 #endif /* !__GENERATING_BOUNDS.H */
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1dd12ae..9c681cc 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -332,7 +332,7 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 				long delta)
 {
 	struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
-	s8 __percpu *p = pcp->vm_node_stat_diff + item;
+	s16 __percpu *p = pcp->vm_node_stat_diff + item;
 	long x;
 	long t;
 
@@ -390,13 +390,13 @@ void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
 void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
 {
 	struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
-	s8 __percpu *p = pcp->vm_node_stat_diff + item;
-	s8 v, t;
+	s16 __percpu *p = pcp->vm_node_stat_diff + item;
+	s16 v, t;
 
 	v = __this_cpu_inc_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v > t)) {
-		s8 overstep = t >> 1;
+		s16 overstep = t >> 1;
 
 		node_page_state_add(v + overstep, pgdat, item);
 		__this_cpu_write(*p, -overstep);
@@ -434,13 +434,13 @@ void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
 void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
 {
 	struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
-	s8 __percpu *p = pcp->vm_node_stat_diff + item;
-	s8 v, t;
+	s16 __percpu *p = pcp->vm_node_stat_diff + item;
+	s16 v, t;
 
 	v = __this_cpu_dec_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v < - t)) {
-		s8 overstep = t >> 1;
+		s16 overstep = t >> 1;
 
 		node_page_state_add(v - overstep, pgdat, item);
 		__this_cpu_write(*p, overstep);
@@ -533,7 +533,7 @@ static inline void mod_node_state(struct pglist_data *pgdat,
        enum node_stat_item item, int delta, int overstep_mode)
 {
 	struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
-	s8 __percpu *p = pcp->vm_node_stat_diff + item;
+	s16 __percpu *p = pcp->vm_node_stat_diff + item;
 	long o, n, t, z;
 
 	do {
-- 
2.7.4