xen: balloon: update the NR_BALLOON_PAGES state

Update the NR_BALLOON_PAGES counter when pages are added to or removed
from the Xen balloon.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Nico Pache <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Cc: Alexander Atanasov <[email protected]>
Cc: Chengming Zhou <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Dexuan Cui <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Juegren Gross <[email protected]>
Cc: Kanchana P Sridhar <[email protected]>
Cc: K. Y. Srinivasan <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Oleksandr Tyshchenko <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: Wei Liu <[email protected]>
Cc: Michael Kelley <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: PacheNico

drivers/xen/balloon.c

@@ -157,6 +157,8 @@ static void balloon_append(struct page *page)
 		list_add(&page->lru, &ballooned_pages);
 		balloon_stats.balloon_low++;
 	}
+	inc_node_page_state(page, NR_BALLOON_PAGES);
+
 	wake_up(&balloon_wq);
 }
 
@@ -179,6 +181,8 @@ static struct page *balloon_retrieve(bool require_lowmem)
 		balloon_stats.balloon_low--;
 
 	__ClearPageOffline(page);
+	dec_node_page_state(page, NR_BALLOON_PAGES);
+
 	return page;
 }