LIRS2

Abstract

A block replacement algorithm keeps receiving attention on improvement of its hit ratio. Many replacement algorithms have been proposed, among which LIRS stands out with its consistently higher hit ratio across various workloads with low time and space overheads. However, there are still access patterns where LIRS produces sub-optimal hit ratio and has room for further improvement. In this paper, we replace the locality measure used by LIRS, the reuse distance, with a more stable and thus more reliable measure, to predict future access time. The new measure is the sum of a block's two recent consecutive reuse distances. It addresses the issue with the reuse distance, which is more likely to fluctuate and mislead replacement decisions. We proposed LIRS2 by incorporating this new measure into the LIRS algorithm to reduce its miss ratio. We further propose a replacement design that allows a responsive adaptation between LIRS2 and LRU so that LRU-friendly access patterns can be well accommodated. We have implemented LLRS2 and its adaptive variant. With extensive experiments on traces from different sources, we show that the algorithms can consistently improve cache miss ratio with low overheads.