Implementation and Performance of Integrated Application-Controlled Caching, Prefetching and Disk Scheduling

Although file caching and prefetching are known techniques to improve the performance of file systems, little work has been done on intergrating caching and prefetching. Optimal prefetching is nontrivial because prefetching may require early cache block replacements. Moreover, the tradeoff between the latency-hiding benefits of prefetching and the increase in the number of fetches required must be considered. This paper presents the design and implementation of a file system that integrates application-controlled caching, prefetching and disk scheduling. We use a two-level cache management strategy. The kernel uses the LRU-SP policy [CFL94a] to allocate blocks to processes, and each process uses the controlledaggressive policy, an algorithm previously shown in a theoretical sense to be near-optimal, for managing its cache. Each process then improves its disk access latency by submitting its prefetches in batches and schedules the requests in each batch to optimize disk access performa..