Application-controlled paging for a shared cache

We consider a cache shared by several concurrently running application processes and propose a provably efficient application-controlled global strategy for the shared cache. Using future information implicitly in the form of good decisions by application processes, we are able to break through the H_k lower bound on competitive ratio proved for classical paging for a k-sized cache in [FKL⁺91]. For a size-k cache shared by P application processes that always make good cache replacement decisions, we develop an online application-controlled paging algorithm with and competitive ratio of 2H_P-1+2 Typically, P is much smaller than k, perhaps by several orders of magnitude. Our competitive ratio improves upon the 2P+2 competitive ratio achieved by [CFL94a]. We show for this problem that no on-line algorithm A can have a competitive ratio better than H_P-1 even if the application processes aiding A have perfect knowledge of individual request sequences. Our results are with respect to a worst-case interleaving of the individual request sequences of the P applications. We introduce a notion of fairness in the more realistic situation when application processes do not always make good cache replacement decisions. We show that our algorithm ensures that no application process needs to evict one of its cached pages to service some page fault caused by a mistake of some other application. Our algorithm is not only fair, but remains efficient; the global paging performance can be bounded in terms of the number of mistakes that application processes make