An efficient page replacement algorithm for PCM-based mobile embedded systems

Traditional embedded systems do not use virtual memory swapping but load the entire footprint into memory as they are usually single task special-purpose machines. Recently, as mobile embedded systems support multi-tasking, the necessity of swapping is becoming increasingly important. However, current mobile systems such as smartphones do not support swapping because flash memory has weaknesses to be a swap device in such environments. More recently, phase-change memory (PCM) emerges as an alternative medium for the swap device of mobile embedded systems. In this paper, we present a new page replacement algorithm for a mobile embedded system that uses PCM as a swap device. Although PCM provides high performance and byte-accessibility, its write operation is slow and it accommodates only limited endurance cycles. To cope with this situation, our algorithm tracks the dirtiness of a page at the granularity of a sub-page and replaces the least dirty page among pages not recently used, leading to reduced write traffic to PCM. Experimental results with various mobile workloads show that the proposed algorithm reduces the amount of data written to PCM by 24% on average and up to 74% compared to the well-known CLOCK algorithm. It also extends the lifetime of PCM by 50% on average.