Linux kernel support to exploit phase change memory

Recently, phase change memory (PRAM) has been developed as a next generation memory technology. Because PRAM can be accessed as word-level using memory interface of DRAM and offer more density compared to DRAM, PRAM is expected as an alternative main memory device. Moreover, it can be used as additional storage of system because of its non-volatility. However, PRAM has several problems. First, the access latency of PRAM is still not comparable to DRAM. It is several times slower than that of DRAM. Second, PRAM can endure hundreds of millions of writes per cell. Therefore, if PRAM does not be managed properly, it has negative impact on the system performance and consistency. In order to solve these problems, we consider the Linux kernel level support to exploit PRAM in memory and storage system. We use PRAM with a small size DRAM and both PRAM and DRAM are mapped into single physical memory address space in Linux. Then, the physical memory pages, which are used by process, are selectively allocated based on the access characteristics. Frequently updated hot segment pages are stored in DRAM. PRAM is used for read only and infrequently updated pages. Consequently, we minimize the performance degradation caused by PRAM while reducing 50% energy consumption of main memory. In addition, the non-volatile characteristic of PRAM is used to support file system. We propose the virtual storage that is a block device interface to share the non-volatile memory pages of PRAM as a storage alternative. By using 256MB PRAM for virtual storage, we can decrease more than 40% of access time of disk.