An Energy-Efficient Virtual Memory System with Flash Memory as the Secondary Storage

• Main Authors: Hung-Wei Tseng, 曾宏偉
• Other Authors: Chia-Lin Yang
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/29405303533502730218

碩士 === 國立臺灣大學 === 資訊工程學研究所 === 93 === Modern operation system often adopts the virtual memory approach to allow the physical memory shared among multiple tasks. Traditional virtual memory system is designed for decades assuming a magnetic disk as the secondary storage. Recently, flash memory becomes a popular storage alternative for many portable devices with the continuing improvements on its capacity, reliability and much lower power consumption than mechanical hard drives. The NAND flash memory is organized with blocks, and each block contains a set of pages. The characteristics of flash memory are quite different from a magnetic disk. Therefore, in this thesis, we revisit virtual memory system design considering limitations imposed by flash memory. In the traditional virtual memory system, a full dirty page is written back to the secondary storage on a page fault. We found that this could result in unnecessary writes thereby wasting energy. We propose the subpaging technique that partitions a page into subunits which has the same size as the flash write unit (flash page). Only dirty subpages are written to flash memory on a page fault. The other issue that we study in this thesis is the storage cache management. Unlike traditional disk cache management, care needs to be taken to guarantee that the flash pages of a main memory page are replaced from the cache in sequence. Experimental results show that the energy reduction of combined subpaging and caching techniques is up to 40%.