The deprecation process of kmem.limit_in_bytes started with the commit
0158115f702 ("memcg, kmem: deprecate kmem.limit_in_bytes") which also
explains in detail the motivation behind the deprecation. To summarize,
it is the unexpected behavior on hitting the kmem limit. This patch
moves the deprecation process to the next stage by disallowing to set
the kmem limit. In future we might just remove the kmem.limit_in_bytes
file completely.

...

@@ -3791,10 +3766,8 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
 			ret = mem_cgroup_resize_max(memcg, nr_pages, true);
 			break;
 		case _KMEM:
-			pr_warn_once("kmem.limit_in_bytes is deprecated and will be removed. "
-				     "Please report your usecase to linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org if you "
-				     "depend on this functionality.\n");
-			ret = memcg_update_kmem_max(memcg, nr_pages);
+			/* kmem.limit_in_bytes is deprecated. */
+			ret = -ENOTSUPP;
 			break;
 		case _TCP:
 			ret = memcg_update_tcp_max(memcg, nr_pages);