A Page Cache Management Scheme for Performance Fairness

現今網路已發展出各式不同的雲端服務及應用，對於雲端服務供應商而言，必須確保使用者能享有穩定且公平的服務品質。另外，資料系統儲存裝置被視為影響整體服務時間的關鍵，也被視為系統效能的最大瓶頸。過去由於固態硬碟的容量較小、價格較高且有壽命限制，以致於無法完全取代傳統機械式硬碟，但近年來固態硬碟技術發展成熟，固態硬碟已逐漸替代傳統硬碟為主要儲存裝置，將大大改善系統整體效能。 在資源共享的雲端環境中，多位使用者競爭共有的記憶體快取空間，由於使用者彼此存取特性的不同，造成了使用者記憶體快取空間分配不均，進而產生使用者效能不公平的情況。因此，本篇論文基於固態硬碟儲存裝置，探討如何公平的分配記憶體快取空間，使得多位使用者能夠獲得公平的效能（Performance fairness）。在此系統中，將會給予每位使用者一個權重值，並根據每位使用者所獲的權重值作為系統資源(記憶體快取空間、使用儲存裝置的時間)分配的標準，並且使用Credit-Based I/O Scheduler來對使用者的 I/O請求收取適當的服務成本，再藉由記錄使用者每週期Read/Write Request的數量和在記憶體快取的Hit ratio，做為下一週期動態調整使用者快取空間的依據，使每位使用者獲得公平的效能，以達成Performance Fairness的目標。Nowadays, as cloud computing has grown in popularity, service providers have developed a variety of different cloud services and applications. For service providers, it is necessary to ensure that users have stable and fair service quality. In addition, storage devices have been recognized as the key of affecting the overall service time and thus considered as the biggest bottleneck of system performance. In the past, due to the small capacity, high price and wear endurance of SSDs, it was impossible to completely replace traditional mechanical hard disks. However, in recent years, solid-state hard disk technology has significant improved. Thus, solid-state hard disks have gradually replaced traditional mechanical hard disks, which greatly improves the overall performance of the computer system. In the cloud environment, resources are shared among users, multiple users would compete for the shared page cache space. Due to the difference user access characteristics, the memory caching space is allocated unevenly, which in turn causes users obtaining unfair performance. Therefore, on the basis on solid-state drives as the storage devices, this paper explores how to allocate memory cache space fairly, so that users can achieve performance fairness. In this system, each user will be given a weight value. The weight value of each user will be used as the standard for system resource allocation. We also use the credit-based I/O Scheduler to charge users for the appropriate service cost of I/O requests. Besides, we record the number of read/write requests for each in each period and calculates the hit ratio of different cache sizes for dynamically adjusting the user cache space in the next period, and finally, the goal of performance fairness can be achieved.第一章 緒論 1 1.1簡介 1 1.2研究動機 2 1.3貢獻 3 1.4論文架構 3 第二章 背景知識與相關研究 4 2.1 Cache partition 4 2.1.1 QoS 規範和優化目標 5 2.1.2 預測方法 6 2.1.3 運作流程 7 2.2 VSSD 8 2.2.1 VSSD 簡介 8 2.2.2 系統架構及方法 10 第三章 系統設計和實作 12 3.1 設計理念 12 3.2 系統架構 13 3.3 模組介紹 14 3.3.1 Weighting模組 14 3.3.2 SSD Credit-Based Scheduler模組 15 3.3.3 I/O Statisticians 模組 18 3.3.4 Page Cache Manager模組 19 3.3.4.1 Page Cache的動態調整方法 19 第四章 實驗結果與討論 25 4.1實驗環境 25 4.2實驗結果 27 4.2.1 C1組合 (multi1 and cscope) 27 4.2.2 C2組合 (cscope and glimpse) 30 第五章 結論與未來工作 34 參考文獻 3