alinux: kidled: make kidled_inc_page_age return latest page age

fix #26416752

The idle page age shown in idle_page_stats is one scan period behind the
theoretical idle age.  The cause is that kidled_inc_page_age returned
the ancient value, instead of the latest value, which leads to not
accounting in corresponding memcg.

This makes kidled_inc_page_age return the increased age of the page,
i.e., the latest page age, when KIDLED_AGE_NOT_IN_PAGE_FLAGS is not set.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>

mm/kidled.c

@@ -75,9 +75,10 @@ int kidled_inc_page_age(pg_data_t *pgdat, unsigned long pfn)
 		if (age >= KIDLED_AGE_MASK)
 			break;
 
+		age++;
 		new = old = page->flags;
 		new &= ~(KIDLED_AGE_MASK << KIDLED_AGE_PGSHIFT);
-		new |= (((age + 1) & KIDLED_AGE_MASK) << KIDLED_AGE_PGSHIFT);
+		new |= ((age & KIDLED_AGE_MASK) << KIDLED_AGE_PGSHIFT);
 	} while (unlikely(cmpxchg(&page->flags, old, new) != old));
 
 	return age;