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July 13th-16th, 2010
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Linux kernel support to exploit phase change memory

Youngwoo Park (

Recently, phase change memory (PRAM) has been developed as a next generation memory technology. PRAM can be access as word-level using memory interface of DRAM and offer more density compare to DRAM. It is expected as an alternative main memory device. Moreover, it can be used as additional storage of system because of its non-volatility.

However, there are several problems of PRAM. First, the access latency of PRAM is still not comparable to DRAM. It is several times slower than those of DRAM and it is different depending on access type (read or write). Second, PRAM can endure hundreds of millions of writes per cell. If PRAM does not be managed properly, PRAM has negative impact on the system performance and consistency.

In order to solve the problems, we consider the Linux kernel level support to exploit PRAM in memory and storage system. First of all, we use PRAM with a small size DRAM and both PRAM and DRAM is 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 page type. Consequently, we minimize the performance degradation and endurance problems caused by PRAM while achieving a large scale main memory using PRAM.

The non-volatile characteristic of PRAM is used to support file system. We propose the file system interface to share the non-volatile memory pages of PRAM as a storage alternative. It give a lot of advantage for file system to access metadata and small size file because it can read or write the data as single word level and avoid unnecessary seek latency of disk.

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