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.h b/mm/slab.h
index b793436..ff39a8f 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -246,12 +246,33 @@
 					     gfp_t gfp, int order,
 					     struct kmem_cache *s)
 {
+	int ret;
+
 	if (!memcg_kmem_enabled())
 		return 0;
 	if (is_root_cache(s))
 		return 0;
-	return __memcg_kmem_charge_memcg(page, gfp, order,
-					 s->memcg_params.memcg);
+
+	ret = __memcg_kmem_charge_memcg(page, gfp, order,
+					s->memcg_params.memcg);
+	if (ret)
+		return ret;
+
+	memcg_kmem_update_page_stat(page,
+			(s->flags & SLAB_RECLAIM_ACCOUNT) ?
+			MEMCG_SLAB_RECLAIMABLE : MEMCG_SLAB_UNRECLAIMABLE,
+			1 << order);
+	return 0;
+}
+
+static __always_inline void memcg_uncharge_slab(struct page *page, int order,
+						struct kmem_cache *s)
+{
+	memcg_kmem_update_page_stat(page,
+			(s->flags & SLAB_RECLAIM_ACCOUNT) ?
+			MEMCG_SLAB_RECLAIMABLE : MEMCG_SLAB_UNRECLAIMABLE,
+			-(1 << order));
+	memcg_kmem_uncharge(page, order);
 }
 
 extern void slab_init_memcg_params(struct kmem_cache *);
@@ -294,6 +315,11 @@
 	return 0;
 }
 
+static inline void memcg_uncharge_slab(struct page *page, int order,
+				       struct kmem_cache *s)
+{
+}
+
 static inline void slab_init_memcg_params(struct kmem_cache *s)
 {
 }