1. A memory scheduler, comprising: a plurality of arbitrators that each select memory requests according to age of the memory requests and whether resources are available for said memory requests; and a second-level arbitrator that selects, for an arbitration round, a series of memory requests made available by said plurality of arbitrators, wherein said second-level arbitrator begins said arbitration round by selecting a memory request from a least recently used (LRU) arbitrator of said plurality of arbitrators.