A cost-aware page replacement algorithm for NAND flash based mobile embedded systems

NAND flash memory is widely used as secondary storage in mobile embedded systems such as cellular phones and digital cameras. These systems usually employ a compressed file system (CFS) to store system files which are fixed during the design phase, in combination with a normal file system to store data files. Since retrieving pages from a CFS requires additional decompression time, it is reasonable to grant them higher priorities when making a page replacement decision. In this paper, we present a new page replacement algorithm for NAND flash memory based embedded systems that considers asymmetric operation cost of each page. The proposed algorithm considers the decompression cost of a page from CFS as well as the asymmetric I/O costs of reads and writes in flash memory. To do this, the algorithm partitions the memory space into a read area, a write area, and a compressed area depending on different operation costs. The size of each area is then dynamically adjusted based on the change of access patterns and the contribution to reducing the I/O costs. Trace-driven simulations show that the proposed algorithm improves the I/O performance of mobile embedded systems significantly. Specifically, it reduces I/O time by 4.8-53.3% compared to widely acknowledged algorithms such as CLOCK, CAR, and CFLRU.