An Empirical Evaluation of Semiconductor File Memory as a Disk Cache

Abstract — This work investigates the application of semiconductor file memory as a disk cache to fill part of the access time gap between disk and main memory. Leveraging DRAM cell technology, block-addressable file memory can lower the overall cost per bit of conventional DRAM due to relaxed design constraints and bad block management. File memory could function in a distinct memory hierarchy stage known as extended storage, which was common in legacy mainframes but should be revisited as a cost-competitive means of improving the performance of modern systems. We have modified the Linux 2.4.18 operating system kernel to emulate file memory in a reserved region of system memory. This experimental model evaluates file memory as an extended storage hierarchy stage that is independent of the effects of the CPU caches and the variablesized page cache. In an analysis of chip cost and performance, if file memory can be at least 27 % less expensive than DRAM and is up to three times slower, it can be used as extended storage to improve performance for typical server loads. I