FastTrack: Foreground App-Aware I/O Management for Improving User Experience of Android Smartphones


Sangwook Shane Hahn, Seoul National University; Sungjin Lee, DGIST; Inhyuk Yee, AIBrain Asia; Donguk Ryu, Samsung Electronics; Jihong Kim, Seoul National University


The quality of user experience on a smartphone is directly affected by how fast a foreground app reacts to user inputs. Although existing Android smartphones properly differentiate a foreground app from background apps for most system activities, one major exception is the I/O service where I/O-priority inversions between a foreground app and background apps are commonly observed. In this paper, we investigate the I/O-priority inversion problem on Android smartphones. From our empirical study with real Android smartphones, we observed that the existing techniques for mitigating I/O-priority inversions are not applicable for smartphones where frequently inverted I/O priorities should be quickly corrected to avoid any user-perceived extra delay. We also identified that most noticeable I/O-priority inversions occur in the page cache and a flash storage device. Based on the analysis results, we propose a foreground app-aware I/O management scheme, called FastTrack, that accelerates foreground I/O requests by 1) preempting background I/O requests in the entire I/O stacks including the storage device and 2) preventing foreground app’s data from being flushed from the page cache. Our experimental results using a prototype FastTrack implementation on four smartphones show that a foreground app can achieve the equivalent level of user-perceived responsiveness regardless of the number of background apps. Over the existing Android I/O implementation, FastTrack can reduce the average user response time by 94% when six I/O-intensive apps run as background apps.

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@inproceedings {215979,
author = {Sangwook Shane Hahn and Sungjin Lee and Inhyuk Yee and Donguk Ryu and Jihong Kim},
title = {{FastTrack}: Foreground {App-Aware} {I/O} Management for Improving User Experience of Android Smartphones},
booktitle = {2018 USENIX Annual Technical Conference (USENIX ATC 18)},
year = {2018},
isbn = {978-1-931971-44-7},
address = {Boston, MA},
pages = {15--28},
url = {},
publisher = {USENIX Association},
month = jul,

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