age array.

We reserve some some bytes for struct rcu_head when a slab
is allocated in this situation.

Changed from V1:
	use VM_BUG_ON instead BUG_ON

Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Í×Ùz—2x