基於效能計數器的非揮發混合式記憶體快取管理優化演算法;Optimization Cache Management Algorithm of Non-Volatile Hybrid Memory Based on Performance Counter

[[abstract]]相變化記憶體 (Phase-Change Memory, PCM) 因為具有非揮發性、相對於 DRAM 高 2 ~ 4 倍的儲存密度、極低的靜態功率消耗、較 Flash Memory 為高的寫入壽命與接近動態隨機存取記憶體 (Dynamic Random Access Memory, DRAM) 的存取速度等特性而備受矚目，有望在未來取代 DRAM 等揮發性記憶體成為主記憶體材料。但因為在現階段製程上 PCM 還存在著為了改變相態而需要較高的電壓產生足夠溫度、較高的寫入延遲，與寫入磨耗的考量等因素，故短時間內要完全取代 DRAM 估計是較難達成的。現今研究趨向於結合兩者的優點，因 DRAM 無限制寫入次數，將 DRAM 作為一個 PCM 的前級快取記憶體，能提高系統反應與透過降低 PCM 寫入次數來增加其壽命。本論文提出的快取管理演算法考量到揮發性記憶體、非揮發性記憶體的壽命、存取速度等特性，使用 CPU 內部效能計數器 (Performance Counter) 所提供的頁面存取頻率資訊對記憶體頁面做分類，進而決定頁面該被放置於何種記憶體材料中能滿足對效能及壽命的最佳化考量。 Phase-Change Memory (PCM), due to its many distinctive features: non-volatile, 2~4 times higher storage density than Dynamic Random Access Memory (DRAM), very low static power consumption, and orders of magnitude better than NAND Flash Memory in read latency, write latency, and write endurance, is expected to replace DRAM and other volatile memory to become the main memory material in the near feature. However, at this stage, the process of PCM manufacturing still has many unfavorable factors on matters such as to change its phase, in need of a higher voltage to produce enough temperature, high write latency and write wear consideration; the complete replacement of DRAM is therefore difficult in a short time. Research today tends to combine the advantage of both, with respect that DRAM has a close to infinite endurance time and its lower access latency; taking DRAM as a pre-cache memory of PCM can improve the system response and increase PCM life span by reducing the number of PCM write.The cache management algorithm proposed in this paper takes information about access frequency of memory page from CPU internal performance counter, consider endurance, access latency and other characteristics to classify memory pages, that then determines which memory material is to be placed to meet the performance and life span of the optimal considerations