Adaptive file caching with application-specific management

Abstract

As disk performance continues to lag behind microprocessors and memory systems, the file system caching has a growing importance in many applications. An effective file system caching can reduce disk accesses significantly. This paper proposes an adaptive and flexible buffer cache management scheme which can handle workloads with various file access characteristics and can exploit applications`` knowledge about their access pattern to improve the file system performance. Most traditional file systems employ a global LRU policy as the buffer replacement policy. The problem with the global LRU policy is that a single global policy, LRU, is applied to all applications without exception and it may not perform well outside the “typical” computing environment. Our solution is the split-level buffer cache management where responsibility of the buffer cache management is split between the kernel and the applications. The kernel provides user applications with a default replacement policy flexible enough to cope with various file access characteristics. Applications can change and customize kernel``s behavior to their needs. For the kernel, we propose a new replacement policy called LRU-RS. Under LRU-RS, the buffer cache is managed in terms of files rather than blocks so as to enforce a different replacement policy for each cached file according to its access pattern. In order to prevent the buffer cache from being wasted by a very long sequential run, a technique of recycling buffers is introduced. In addition, an adaptive recycling technique is also employed to distinguish between frequently-accessed and infrequently-accessed large files with a small amount of the buffer cache. For application-specific management, we propose a set of flexible interfaces through which applications can exert fine control over the buffer replacement management. System call interfaces are employed in order to minimize interactions between the kernel and applications but not to add to t...