!949 mm: page_counter: remove unneeded atomic ops for low/min

Merge Pull Request from: @ci-robot 
 
PR sync from:  Peng Zhang <zhangpeng362@huawei.com>
 https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/thread/KYRABPTSB6EKOTCKUIGSLAPKEFA5O5FS/ 
 
 
Link:https://gitee.com/openeuler/kernel/pulls/949 

Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com> 
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> 

mm/page_counter.c

@@ -17,24 +17,23 @@ static void propagate_protected_usage(struct page_counter *c,
 				      unsigned long usage)
 {
 	unsigned long protected, old_protected;
-	unsigned long low, min;
 	long delta;
 
 	if (!c->parent)
 		return;
 
-	min = READ_ONCE(c->min);
-	if (min || atomic_long_read(&c->min_usage)) {
-		protected = min(usage, min);
+	protected = min(usage, READ_ONCE(c->min));
+	old_protected = atomic_long_read(&c->min_usage);
+	if (protected != old_protected) {
 		old_protected = atomic_long_xchg(&c->min_usage, protected);
 		delta = protected - old_protected;
 		if (delta)
 			atomic_long_add(delta, &c->parent->children_min_usage);
 	}
 
-	low = READ_ONCE(c->low);
-	if (low || atomic_long_read(&c->low_usage)) {
-		protected = min(usage, low);
+	protected = min(usage, READ_ONCE(c->low));
+	old_protected = atomic_long_read(&c->low_usage);
+	if (protected != old_protected) {
 		old_protected = atomic_long_xchg(&c->low_usage, protected);
 		delta = protected - old_protected;
 		if (delta)