I always prefer shorter names, but mem_cgroup, and not memcg, seems to be the default for external functions.}I suggest that the naming consistently follow the model
>+
>+#define mem_cgroup_kmem_on 0
>+#define __mem_cgroup_new_kmem_page(a, b, c) false
>+#define __mem_cgroup_free_kmem_page(a,b )
>+#define __mem_cgroup_commit_kmem_page(a, b, c)
"mem_cgroup_kmem_foo". So "mem_cgroup_kmem_" becomes the well-known
identifier for this subsystem.
Then, s/mem_cgroup/memcg/g/ - show us some mercy here!