Browsing by Author "Sung, Po-Han"

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Eager Synching: A Selective Logging Strategy for Fast fsync() on Flash-Based Android Devices
(2017-04-01)
Chang, Li-Pin
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Sung, Po-Han
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Chen, Po-Tsang
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Chen, Po-Hung
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資訊工程學系
Flash storage has been a standard component in Android devices. Recent research has reported that application data management in Android involves frequent fsync() operations. The current fsync() implementations, including those of ext4 and F2FS, have several common drawbacks. Specifically, ext4 commits a transaction every time to sync a file, whereas F2FS commits a checkpoint to sync a directory. Committing a transaction or checkpoint flushes all dirty data from the page cache to the flash storage via many small, random block write requests. The resultant high I/O frequency and excessive write traffic cause a high fsync() latency. This study presents an efficient fsync() method, called eager synching, which is based on a simple idea: write less, and write sequentially. To sync a file, eager synching writes only a subset of all dirty data in the page cache to a sequential log space using a few sequential block write requests. It does not involve transaction or checkpoint committing. We successfully implemented eager synching in ext4 and F2FS, and our experimental results show that, compared with the original fsync() methods of ext4 and F2FS, eager synching reduced the average and maximum fsync() latencies by up to 72% and 91%, respectively, block-level write traffic by up to 35%, and I/O frequency by up to 66%. Through enhanced crash recovery procedures, eager synching can successfully recover all previously synched files while still guaranteeing the file system integrity. We also conducted live application replays using the proposed eager synching approach and observed that this approach significantly improved the application frame updating rate and application execution time.
Fast File Synching for Applications in Flash-Based Android Devices
(2014-01-01)
Chang, Li-Pin
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Sung, Po-Han
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Chen, Po-Hung
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交大名義發表
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National Chiao Tung University
Flash-storage-based Android devices have been a very popular design option for hand-held devices. Recent research pointed out that application-level data management in Android systems involves frequent file synching operations (i.e., fsync() calls). Because fsync() is a blocking call, applications could suffer from poor response if the fsync() implementation is inefficient. The existing methods of file synching in Android systems are not flash-aware, and they could either significantly increase the block-level write randomness or excessively increase the block write traffic. This work introduces an efficient design of fsync(), called eager synching. Our basic idea is simple: write less, and write sequentially. When a file is being synched, eager synching first identifies the dirty data related to the file, and then write the dirty data to a sequential log space. This way, fsync() calls can be quickly serviced by a small amount of fast, sequential block writes on the flash storage. Our experimental results show that, under the workloads of typical Android applications, the average and max fsync() latencies were reduced by up to 72% and 91%, respectively, and the block-level write traffic was reduced by up to 35%.