Exploiting Gray-Box Knowledge of Buffer-Cache Management

The buffer-cache replacement policy of the OS can have a significant impact on the performance of I/Ointensive applications. In this paper, we introduce a simple fingerprinting tool, Dust, which uncovers the replacement policy of the OS. Specifically, we are able to identify how initial access order, recency of access, frequency of access, and long-term history are used to determine which blocks are replaced from the buffer cache. We show that our fingerprinting tool can identify popular replacement policies described in the literature (e.g., FIFO, LRU, LFU, Clock, Random, Segmented FIFO, 2Q, and LRU-K) as well as those found in current systems (e.g., NetBSD, Linux, and Solaris). We demonstrate the usefulness of fingerprinting the cache replacement policy by modifying a web server to use this knowledge; specifically, the web server infers the contents of the OS file cache by modeling the replacement policy under the given set of page requests. We show that by first servicing those web pages that are believed to be resident in the OS buffer cache, we can improve both average response time and throughput.