shrink_work
struct work_struct shrink_work;
struct dm_bufio_client *c = container_of(w, struct dm_bufio_client, shrink_work);
queue_work(dm_bufio_wq, &c->shrink_work);
INIT_WORK(&c->shrink_work, shrink_work);
flush_work(&c->shrink_work);
flush_work(&c->shrink_work);