US Patent 7769953 Variable cache data retention system

A customizable cache discard policy is provided which reduces adverse consequences of conventional discard policies. In a data processing system, a cache controller invokes a cache data discard policy as the cache approaches its capacity. Using one possible policy, data having the shortest retrieval (fetch) time is discarded before data having longer retrieval times. In an alternative policy, data may be discarded based upon its source. Weightings may be applied based upon the distance from each source to the cache, may be based upon priorities assigned to each source, or may be based upon the type of each source.