用於Android裝置中快閃式儲存裝置之快速檔案同步

Abstract

手持裝置已經成為每個人生活中的一部分，其中以Android為主要使用在手持裝置上的作業系統。最近的研究指出Android上的應用程式在存取資料時會涉及大量的檔案資料同步作業，其為造成寫入效能的嚴重低落。這項研究提出了一個有效率的檔案同步作業的實作方式，稱為"eager synching"，以用於搭配快閃式儲存記憶體的Android裝置上。基本方法很簡單：檔案同步作業時，我們只把該檔案的相關資料寫入一個循序的紀錄空間，降低檔案同步作業的寫入隨機性。這是因為比起隨機寫入，快閃式記憶體較擅長處理循序寫入，這樣的設計可以使檔案同步作業的延遲性降低。我們實作了"eager synching"至ext4檔案系統上，實驗結果顯示到真實應用程式以及儲存系統評測軟體的寫入效能提升了高達50%，最大的寫入循序性改進量為55%。

Using hand-held devices is now a part of peoples' lives. Android is one among the most popular operating systems for hand-held devices. Recent research pointed out that application data manipulation in Android systems involves a great deal of file synching operations, which poses a severe negative impact to the write performance. This work introduces an efficient implementation of file synching operations, called \textit{eager synching}, for Android devices equipped with flash storage. The basic idea is simple: when a file is being synched, eager synching writes only the dirty data associated with the file in a sequential log space, reducing the randomness in the write pattern of file synching. Because sequential write is significantly faster than random write in flash storage, this design can effectively reduce the latency of file synching operations. We implemented our eager synching in the ext4 file system, and the experimental results show that the write throughput of real Android applications and storage benchmarks were improved by up to 50\%, and the largest improvement in write sequentiality was 55\%.