mm: use for_each_online_cpu() in vmstat

The sum_vm_events passes cpumask for for_each_cpu().  But it's useless
since we have for_each_online_cpu.  Althougth it's tirival overhead, it's
not good about coding consistency.

Let's use for_each_online_cpu instead of for_each_cpu with cpumask
argument.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmstat.c

@@ -22,14 +22,14 @@
 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
 EXPORT_PER_CPU_SYMBOL(vm_event_states);
 
-static void sum_vm_events(unsigned long *ret, const struct cpumask *cpumask)
+static void sum_vm_events(unsigned long *ret)
 {
 	int cpu;
 	int i;
 
 	memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));
 
-	for_each_cpu(cpu, cpumask) {
+	for_each_online_cpu(cpu) {
 		struct vm_event_state *this = &per_cpu(vm_event_states, cpu);
 
 		for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
@@ -45,7 +45,7 @@ static void sum_vm_events(unsigned long *ret, const struct cpumask *cpumask)
 void all_vm_events(unsigned long *ret)
 {
 	get_online_cpus();
-	sum_vm_events(ret, cpu_online_mask);
+	sum_vm_events(ret);
 	put_online_cpus();
 }
 EXPORT_SYMBOL_GPL(all_vm_events);