vmstat: use raw_cpu_ops to avoid false positives on preemption checks

vm counters are allowed to be racy.  Use raw_cpu_ops to avoid the
local_irq_disable overhead and to avoid preemption checks which will be
added to the __this_cpu operations.

[akpm@linux-foundation.org: Add comment.  Again.]
Signed-off-by: Christoph Lameter <cl@linux.com>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/vmstat.h

@@ -27,9 +27,13 @@ struct vm_event_state {
 
 DECLARE_PER_CPU(struct vm_event_state, vm_event_states);
 
+/*
+ * vm counters are allowed to be racy. Use raw_cpu_ops to avoid the
+ * local_irq_disable overhead.
+ */
 static inline void __count_vm_event(enum vm_event_item item)
 {
-	__this_cpu_inc(vm_event_states.event[item]);
+	raw_cpu_inc(vm_event_states.event[item]);
 }
 
 static inline void count_vm_event(enum vm_event_item item)
@@ -39,7 +43,7 @@ static inline void count_vm_event(enum vm_event_item item)
 
 static inline void __count_vm_events(enum vm_event_item item, long delta)
 {
-	__this_cpu_add(vm_event_states.event[item], delta);
+	raw_cpu_add(vm_event_states.event[item], delta);
 }
 
 static inline void count_vm_events(enum vm_event_item item, long delta)