linux_kmem_rcu
struct linux_kmem_rcu *rcu =
container_of(head, struct linux_kmem_rcu, rcu_head);
size += sizeof(struct linux_kmem_rcu);
struct linux_kmem_rcu *rcu = LINUX_KMEM_TO_RCU(c, m);
((struct linux_kmem_rcu *)((char *)(m) + \
(c)->cache_size - sizeof(struct linux_kmem_rcu)))
((void *)((char *)(r) + sizeof(struct linux_kmem_rcu) - \
struct linux_kmem_rcu *rcu = LINUX_KMEM_TO_RCU(c, mem);