bpf: Memcg-based memory accounting for bpf maps

This patch enables memcg-based memory accounting for memory allocated
by __bpf_map_area_alloc(), which is used by many types of bpf maps for
large initial memory allocations.

Please note, that __bpf_map_area_alloc() should not be used outside of
map creation paths without setting the active memory cgroup to the
map's memory cgroup.

Following patches in the series will refine the accounting for
some of the map types.
Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201201215900.3569844-8-guro@fb.com

kernel/bpf/syscall.c

@@ -268,6 +268,10 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
 	return err;
 }
 
+/* Please, do not use this function outside from the map creation path
+ * (e.g. in map update path) without taking care of setting the active
+ * memory cgroup (see at bpf_map_kmalloc_node() for example).
+ */
 static void *__bpf_map_area_alloc(u64 size, int numa_node, bool mmapable)
 {
 	/* We really just want to fail instead of triggering OOM killer
@@ -280,7 +284,7 @@ static void *__bpf_map_area_alloc(u64 size, int numa_node, bool mmapable)
 	 * __GFP_RETRY_MAYFAIL to avoid such situations.
 	 */
 
-	const gfp_t gfp = __GFP_NOWARN | __GFP_ZERO;
+	const gfp_t gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_ACCOUNT;
 	unsigned int flags = 0;
 	unsigned long align = 1;
 	void *area;