User-level Control of Block-level Cache Aggressiveness

Abstract

Using an SSD device as a cache for an HDD device is a widely used method in current information systems. In Linux systems, dm-cache is a commonly used block-level storage cache implementation. It replaces cache blocks according to an advanced policy, called SMQ (Stochastic MultiQueue). SMQ's stochastic nature allows it to perform well for many different storage access patterns, but not always optimally and sometimes poorly. In particular, the policy can be either reluctant or too eager to cache data. We propose a method to enable control of the aggressiveness of caching in dm-cache. It provides an interface in the user space to control replacement aggressiveness in kernel space. Our experimental evaluation shows that the proposed method improves the I/O performance in a microbenchmark and an application benchmark.