Ji-hyun In

SWL: a search-while-load demand paging scheme with NAND flash memory

As mobile phones become increasingly multifunctional, the number and size of applications installed in phones are rapidly increasing. Consequently, mobile phones require more hardware resources such as NOR/NAND flash memory and DRAM, and their production cost is accordingly becoming higher. One candidate solution to reduce production cost is demand paging using MMU. However, demand paging causes unpredictably long page fault latency, and as such mobile phone manufacturers are reluctant to deploy this scheme. In this paper, we present a method that reduces the long latency of page faults by performing page fault handling in a parallelized manner, considering the characteristics of NAND-Type flash memory. We also discuss how to modify the existing page cache replacement policies so that they can exploit the benefits of the parallelized page fault handler. Experimental results show that the parallelized page fault handler improves the worst case latency of page faults significantly, by up to roughly 20%, and that the modified page cache replacement policies improve both the average and worst instruction fetch time.

Virtual-ROM: a new demand paging component for RTOS and NAND flash memory based mobile devices

Similiar to a hard disk, NAND flash memory must be accessed in sector unit, and cannot be used for code storage without copying its contents to RAM. A virtual memory technique is promising as a RAM saving solution. However, it can not be easily used without the operating system supports, and it is not suitable for real time systems because it causes unpredicted execution delays. Virtual-ROM is a light-weight demand paging solution designed for RTOS based mobile devices. It is OS-independent, easy-to-use, and well optimized for NAND flash memory. Because it occupies only a restricted address space, real time tasks can be free from unpredictable execution delays by being excluded from Virtual-ROM. Our trace driven simulation showed that its performance is similar to 70ns NOR flash memory, and our real taget adaptation for a CDMA mobile phone showed that it saved about 30% RAM usage.