mm: page_counters: initialize usage using ATOMIC_LONG_INIT() macro

When a page_counter structure is initialized, there is no need to use an
atomic set operation to initialize the usage counter because at this point
the structure is not visible to anybody else.  ATOMIC_LONG_INIT() is what
should be used in such cases.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Roman Gushchin <[email protected]>
Acked-by: Shakeel Butt <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: rgushchin

include/linux/page_counter.h

@@ -52,7 +52,7 @@ static inline void page_counter_init(struct page_counter *counter,
 				     struct page_counter *parent,
 				     bool protection_support)
 {
-	atomic_long_set(&counter->usage, 0);
+	counter->usage = (atomic_long_t)ATOMIC_LONG_INIT(0);
 	counter->max = PAGE_COUNTER_MAX;
 	counter->parent = parent;
 	counter->protection_support = protection_support;