Improving the efficiency of UNIX file buffer caches

Abstract

This paper reports on the effects of using hardware virtual memory assists in managing file buffer caches in UNIX. A controlled experimental environment was constructed from two systems whose only difference was that one of them (XMF) used the virtual memory hardware to assist file buffer cache search and retrieval. An extensive series of performance characterizations was used to study the effects of varying the buffer cache size (from 3 Megabytes to 70 MB); I/O transfer sizes (from 4 bytes to 64 KB); cache-resident and non-cache-resident data; READs and WRITEs; and a range of application programs. The results: small READ/WRITE transfers from the cache (≤1 KB) were 50% faster under XMF, while larger transfers (≥8 KB) were 20% faster. Retrieving data from disk, the XMF improvement was 25% and 10% respectively, although OPEN/CLOSE system calls took slightly longer in XMF. Some individual programs ran as much as 40% faster on XMF, while an application benchmark suite showed a 7-15% improvement in overall execution time. Perhaps surprisingly, XMF had fewer translation lookaside buffer misses.