Lookahead page placement

Historically, the majority of virtual storage operating systems have used random virtual page placement. Random placement interacts undesirably with a direct-mapped cache to produce cache conflict misses, some of which could be avoided by making better placement decisions. Recently, several studies on careful page placement as an alternative to random placement have shown that a direct-mapped cache managed with careful placement performs nearly as well as a two-way set-associative cache under random placement. Towards a performance evaluation methodology for careful page placement, we propose two new classes of theoretical page placement policies for direct-mapped caches based on memory reference string lookahead. Lookahead page placement is a systems modeling tool for evaluating nonlookahead policy performance and providing insight into potential gains that might be achieved with improved nonlookahead policies. Strict lookahead policies perform virtual page mappings using only memory reference lookahead information. Hybrid lookahead policies combine existing careful page placement methods with future knowledge obtained through lookahead. Our lookahead policies use greedy, polynomial-time bin selection procedures to assign virtual pages to cache bins having favorable future usage characteristics. Trace-driven simulation is used to compare three different lookahead policies against several nonlookahead page placement policies for three multiprogrammed UNIX workloads.