mm: memcontrol: report slab usage in cgroup2 memory.stat

Show how much memory is used for storing reclaimable and unreclaimable
in-kernel data structures allocated from slab caches.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/slab.c b/mm/slab.c
index 852fc5c..56dd0df 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1442,9 +1442,10 @@
  */
 static void kmem_freepages(struct kmem_cache *cachep, struct page *page)
 {
-	const unsigned long nr_freed = (1 << cachep->gfporder);
+	int order = cachep->gfporder;
+	unsigned long nr_freed = (1 << order);
 
-	kmemcheck_free_shadow(page, cachep->gfporder);
+	kmemcheck_free_shadow(page, order);
 
 	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
 		sub_zone_page_state(page_zone(page),
@@ -1461,7 +1462,8 @@
 
 	if (current->reclaim_state)
 		current->reclaim_state->reclaimed_slab += nr_freed;
-	__free_kmem_pages(page, cachep->gfporder);
+	memcg_uncharge_slab(page, order, cachep);
+	__free_pages(page, order);
 }
 
 static void kmem_rcu_free(struct rcu_head *head)