Many-core CPUs require many parallel computation tasks to reach their full potential because CPU cores become idle if they do not have enough computation tasks. How best to utilize a number of cores in many-core CPUs should be examined. In this paper, we propose exploitation of idle cores for improving file access performance. Idle cores are used to extract file access patterns from access logs and the extracted patterns are used to improve file cache efficiency by reordering the LRU (Least Recently Used) list based on the extracted patterns. Data mining techniques are used to extract access patterns to reduce computation overhead. Our method was evaluated by simulation and also implemented on Linux kernel 2.6.26 as a prototype system. In the simulation experiment, our method improved the cache-hit ratio up to 1.09% on DBT-2 (TPC-C) trace logs. Our prototype implementation on Linux improves DBT-2 performance up to 5.24% on a real machine.