On Fri, 10 Aug 2007 15:47:59 +0400
xemul@openvz.org wrote:

>  struct pid
>  {
>  	atomic_t count;
> @@ -50,6 +50,8 @@ struct pid
>  	/* lists of tasks that use this pid */
>  	struct hlist_head tasks[PIDTYPE_MAX];
>  	struct rcu_head rcu;
> +	int level;
> +	struct upid numbers[1];

You can make this have size [0] now.  It's a gcc extension and
is used elsewhere in the kernel.