省電型快閃記憶體儲存系統設計

目前的作業系統多半利用虛擬記憶體的方法，讓許多程式能夠在有限的主記憶體空間中多工執行。數十年來，作業系統也都預設電腦中所使用磁碟機作為儲存媒體。近年來，隨著技術的進步，快閃記憶體(flash memory)也逐漸褪去以往高價的形象，在輕巧性、可靠度以及容量上不斷地提升，加以其低於硬碟機的電源消耗，被廣泛地利用在對電源消耗及重量都有極嚴苛要求的各種攜帶型裝置中。目前的快閃記憶體應用有逐漸以NAND型記憶體為主流的趨勢。NAND型快閃記憶體是數個「區塊(block) 」所組成，而每個區塊又分為數個「頁(page)」﹔此外，快閃記憶體還具有許多不同於磁碟機的特性。對此，在這篇論文中，我們重新審視傳統的虛擬記憶體系統設計。在傳統的虛擬記憶體系統中，當發生了分頁錯誤(page fault)的時候，被取代的主記憶體頁(main memory page)將會整個被寫回儲存媒體中。然而，經過觀察後發現，這種行為往往導致了許多不必要的寫入動作，也增加了不必要的電源消耗。因此，我們提出了subpaging的辦法，將一個主記憶體頁切割成數個與快閃記憶體頁同大小的區塊。一旦發生了分頁錯誤的時候，僅有被標記為「已更動」的小區塊會被寫回快閃記憶體。另外，我們也探討了儲存裝置的快取記憶體管理機制。不同於傳統的磁碟快取，寫入是快閃記憶體更加需要重視的動作，同時，也要確保從快取記憶體寫回快閃記憶體時，資料的連續性問題。實驗的結果顯示，利用subpaging 跟改進過的快取記憶體機制，能省下40%快閃記憶體系統的耗電量。

關鍵字

虛擬記憶體系統；儲存裝置；快閃記憶體

並列摘要

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%.

並列關鍵字

Virtual Memory System ； Storage System ； Flash Memory

參考文獻

[3] L.-P. Chang and T.-W. Kuo, “An adaptive striping architecture for flash memory storage systems of embedded systems,” in Proceedings of The 8th IEEE Real-Time

and Embedded Technology and Applications Symposium, pp. 24–27, September 2002.

[5] C. Park, J.-U. Kang, S.-Y. Park, and J.-S. Kim, “Energy-aware demand paging on NAND flash-based embedded storages,” in Proceedings of the IEEE/ACM International

Symposium on Low Power Electronics and Design, Auguest 2004.

to branch prediction,” in Proceedings of the 2002 International Symposium on High-Performance Computer Architecture, pp. 233–246, February 2002.

國際替代計量

省電型快閃記憶體儲存系統設計

全文下載

主題瀏覽