Revealing applications' access pattern in collective I/O for cache management

Collective I/O is a critical I/O strategy on high-performance parallel computing systems that enables programmers to reveal parallel processes' I/O accesses collectively and makes possible for the parallel I/O middleware to carry out I/O requests in a highly efficient manner. Collective I/O has been proven as a core parallel I/O optimization technique. However, due to the collective nature of collective I/O, the access pattern of each individual process can be lost after I/O requests are aggregated at the parallel I/O middleware layer. In this study, we analyze this issue in detail. We show that such lost access pattern can have a negative impact on underlying caching algorithms' view of locality and can result in many unnecessary cache misses in low level buffer caches and additional disk accesses. To address this issue, we propose to reveal unseen access patterns - performing collective I/O but more importantly retaining applications' access patterns to underlying cache management. With such an idea, we have prototyped a new collective I/O aware cache management methodology. The evaluations with various cache management algorithms have confirmed clear advantages over the existing collective I/O strategy that throws away applications' original access pattern.