[PATCH] mm/vmstat: don't do count if no needs

[Alex Shi <alex.shi@linux.alibaba.com>]

For couple of vmstat account funcs, the caller usually doesn't check the
delta value, if delta == 0, irq or atomic operator is a waste. That's
better to be skipped.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org> 
Cc: linux-mm@kvack.org 
Cc: linux-kernel@vger.kernel.org 
---
 mm/vmstat.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3fb23a21f6dd..91f28146daa7 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -321,6 +321,9 @@ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 	long x;
 	long t;
 
+	if (!delta)
+		return;
+
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -341,6 +344,9 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 	long x;
 	long t;
 
+	if (!delta)
+		return;
+
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -484,6 +490,9 @@ static inline void mod_zone_state(struct zone *zone,
 	s8 __percpu *p = pcp->vm_stat_diff + item;
 	long o, n, t, z;
 
+	if (!delta)
+		return;
+
 	do {
 		z = 0;  /* overflow to zone counters */
 
@@ -518,6 +527,9 @@ static inline void mod_zone_state(struct zone *zone,
 void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 			 long delta)
 {
+	if (!delta)
+		return;
+
 	mod_zone_state(zone, item, delta, 0);
 }
 EXPORT_SYMBOL(mod_zone_page_state);
@@ -541,6 +553,9 @@ static inline void mod_node_state(struct pglist_data *pgdat,
 	s8 __percpu *p = pcp->vm_node_stat_diff + item;
 	long o, n, t, z;
 
+	if (!delta)
+		return;
+
 	do {
 		z = 0;  /* overflow to node counters */
 
@@ -581,6 +596,9 @@ EXPORT_SYMBOL(mod_node_page_state);
 
 void inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
 {
+	if (!delta)
+		return;
+
 	mod_node_state(pgdat, item, 1, 1);
 }
 
@@ -604,6 +622,9 @@ void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 {
 	unsigned long flags;
 
+	if (!delta)
+		return;
+
 	local_irq_save(flags);
 	__mod_zone_page_state(zone, item, delta);
 	local_irq_restore(flags);
@@ -647,6 +668,9 @@ void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 {
 	unsigned long flags;
 
+	if (!delta)
+		return;
+
 	local_irq_save(flags);
 	__mod_node_page_state(pgdat, item, delta);
 	local_irq_restore(flags);
-- 
2.18.4