mm: page_alloc: batch vmstat updates in expand()

expand() currently updates vmstat for every subpage.  This is unnecessary,
since they're all of the same zone and migratetype.

Count added pages locally, then do a single vmstat update.

Link: https://lkml.kernel.org/r/20240327190111.GC7597@cmpxchg.orgSigned-off-by: Johannes Weiner <hannes@cmpxchg.org>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -1335,6 +1335,7 @@ static inline void expand(struct zone *zone, struct page *page,
 	int low, int high, int migratetype)
 {
 	unsigned long size = 1 << high;
+	unsigned long nr_added = 0;
 
 	while (high > low) {
 		high--;
@@ -1350,9 +1351,11 @@ static inline void expand(struct zone *zone, struct page *page,
 		if (set_page_guard(zone, &page[size], high))
 			continue;
 
-		add_to_free_list(&page[size], zone, high, migratetype, false);
+		__add_to_free_list(&page[size], zone, high, migratetype, false);
 		set_buddy_order(&page[size], high);
+		nr_added += size;
 	}
+	account_freepages(zone, nr_added, migratetype);
 }
 
 static void check_new_page_bad(struct page *page)