Cache Management with Fadvise Based on LFU

Abstract

Virtualization is used for various purposes such as cloud computing and a virtualized environment has been one of the most important platforms. In many virtualized environments, access to its persistent storage device, e.g. hard disk drive (HDD) or solid-state drive (SSD), is performed via two caches, which are page caches of guest and host operating systems. Both caches are usually managed based on the least recently used (LRU) algorithm. Previous work demonstrated that accesses to the host operating system page cache have a negative temporal locality of reference in these cases. Namely, an accessed block will probably not be accessed again in the near future. This locality severely decreases the hit ratio of a host operating system page cache. For addressing this issue, a method for improving the locality of reference in the accesses in the host operating system page cache by fixing data stored in the guest operating system page cache was proposed. However, the method assumed that the hot spot, which is the data area aggressively accessed, was given. Because of this limitation, the method can rarely be used. In this paper, we propose a method for improving the hit ratio of a host operating system page cache by enhancing the locality of reference at the cache. First, we explain the negative temporal locality of reference in virtualized environments. Second, we propose a method for enhancing the locality of reference in the host operating system page cache for improving its hit ratio without an assumption that its hotspot is given. This method observes file accesses in the system using an operating system kernel function and automatically detects the hotspot. This then stores the area in the guest operating system page cache. As a result, the locality of reference in the host operating system cache increases. Lastly, we evaluate this proposed method, then show that this method outperforms the normal method and can provide comparable performance with an existing method even if the hot spot is not given.