bpf: Refine memcg-based memory accounting for xskmap maps

Extend xskmap memory accounting to include the memory taken by
the xsk_map_node structure.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201201215900.3569844-18-guro@fb.com

net/xdp/xskmap.c

@@ -16,7 +16,8 @@ static struct xsk_map_node *xsk_map_node_alloc(struct xsk_map *map,
 {
 	struct xsk_map_node *node;
 
-	node = kzalloc(sizeof(*node), GFP_ATOMIC | __GFP_NOWARN);
+	node = bpf_map_kzalloc(&map->map, sizeof(*node),
+			       GFP_ATOMIC | __GFP_NOWARN);
 	if (!node)
 		return ERR_PTR(-ENOMEM);