sched/idle: Move quiet_vmstate() into the NOHZ code

quiet_vmstat() is an expensive function that only makes sense when we
go into NOHZ.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: aubrey.li@linux.intel.com
Cc: cl@linux.com
Cc: fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/idle.c

@@ -219,7 +219,6 @@ static void do_idle(void)
 	 */
 
 	__current_set_polling();
-	quiet_vmstat();
 	tick_nohz_idle_enter();
 
 	while (!need_resched()) {

kernel/time/tick-sched.c

@@ -27,6 +27,7 @@
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
 #include <linux/context_tracking.h>
+#include <linux/mm.h>
 
 #include <asm/irq_regs.h>
 
@@ -787,6 +788,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 	if (!ts->tick_stopped) {
 		calc_load_nohz_start();
 		cpu_load_update_nohz_start();
+		quiet_vmstat();
 
 		ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
 		ts->tick_stopped = 1;