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A Caching Filesystem for Increasing Locality in the Second Cache in a Virtualized Environment

Virtualized environments with virtual machines are widely used in various situations such as cloud computing. In these environments, two caches are utilized for disk accesses. One is a guest operating system page cache and the other is a host operating system page cache. In this situation, the accesses to the host operating system page cache have negative temporal locality of reference and the hit ratio of the host operating system cache is severely decreased by this locality. In this study, we propose a novel filesystem for increasing the hit ratio of a host operating system cache. The filesystem works in a guest operating system and manages memory instead of page cache. The filesystem stably retains certain data and does not replace them. As a result, the accesses to some data always result in a cache hit, while the accesses to other data always result in a cache miss. Therefore, the locality of reference of accesses to host operating system page cache is increased, and its hit ratio is expected to improve. We implement the proposed filesystem and evaluate its performance. Our evaluation demonstrates that the filesystem can significantly improve the host operating system page cache hit ratio and I/O performance in a virtualized environment.