With cloud assistance, mobile apps can offload their resource-demanding computation tasks to the cloud. This leads to a scenario where computation tasks in the same program run concurrently on both the mobile device and the cloud. An important challenge is to ensure that the tasks are able to access and share the files on both the mobile and the cloud in a manner that is efficient, consistent, and transparent to locations. Existing distributed file systems and network file systems do not satisfy these requirements. Current systems for offloading tasks either do not support file access for offloaded tasks or do not offload tasks with file access. The paper addresses this issue by designing and implementing an application-level file system called Overlay File System (OFS). To improve efficiency, OFS maintains and buffers local copies of data sets on both the cloud and the mobile device. OFS ensures consistency and guarantees that all the reads get the latest data. It combines write-invalidate and write-update policies to effectively reduce the network traffic incurred by invalidating/updating stale data copies and to reduce the execution delay when the latest data cannot be accessed locally. To guarantee location transparency, OFS creates a unified view of the data that is location independent and is accessible as local storage. We overcome the challenges caused by the special features of mobile systems on an application-level file system, like the lack of root privilege and state loss when application is killed due to the shortage of resource and implement an easy to deploy prototype of OFS. The paper tests the OFS prototype on Android OS with a real mobile app and real mobile user traces. Extensive experiments show that OFS can effectively support consistent file accesses from computation tasks, no matter whether they are on a mobile device or offloaded to the cloud. In addition, OFS reduce both file access latency and network traffic incurred by file accesses.

中文翻译：

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云辅助移动应用覆盖文件系统的设计与实现

借助云的帮助，移动应用程序可以将其对资源要求高的计算任务卸载到云中。这导致了同一程序中的计算任务在移动设备和云上同时运行的场景。一个重要的挑战是确保任务能够以高效、一致且对位置透明的方式访问和共享移动设备和云上的文件。现有的分布式文件系统和网络文件系统不能满足这些要求。当前用于卸载任务的系统要么不支持卸载任务的文件访问，要么不通过文件访问卸载任务。本文通过设计和实现一个称为覆盖文件系统 (OFS) 的应用程序级文件系统来解决这个问题。为了提高效率，OFS 在云和移动设备上维护和缓冲数据集的本地副本。OFS 保证一致性，保证所有读取得到最新数据。它结合了写无效和写更新策略，以有效减少因失效/更新陈旧数据副本而导致的网络流量，并减少本地无法访问最新数据时的执行延迟。为了保证位置透明性，OFS 创建了一个与位置无关且可作为本地存储访问的统一数据视图。我们克服了移动系统在应用级文件系统上的特殊性所带来的挑战，例如缺乏root权限和由于资源短缺而导致应用程序被杀死时状态丢失，并实现了易于部署的OFS原型。本文使用真实的移动应用程序和真实的移动用户轨迹在 Android 操作系统上测试 OFS 原型。大量实验表明，OFS 可以有效地支持来自计算任务的一致文件访问，无论它们是在移动设备上还是卸载到云端。此外，OFS 减少了文件访问延迟和文件访问引起的网络流量。