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Compressed file systems are suitable for portable consumer devices with small capacity of storage systems because the contents of files are stored as a compressed form to save the space of storage. The portable consumer devices also exploit demand paging mechanism to cut down their cost and size. However, if the portable consumer devices use the compressed file systems, there are large computational and I/O overheads. When data are requested, the data should be decompressed before they are accessed by application programs. This is the computational overhead of compressed file systems. And also, to decompress only one byte data, several data should be copied to the main memory from the secondary storage. That is the I/O overhead. To overcome these overheads, this work proposes a new replacement and swapping strategy for the portable consumer devices using the compressed file systems, which keeps the frequently accessed data in the main memory as long as possible and stores the uncompressed data of compressed file systems in the swap space so that serves them directly from the swap space. This strategy increases the page hit ratio, and reduces several copying operations and a decompressing operation of compressed file systems. As a result, it could improve the read performance of portable consumer devices. Trace-driven simulations with real traces show that the proposed replacement and swapping strategy performs better than existing replacement and swapping mechanism in terms of the total read I/O performance, page fault ratio, and page fault latency.
Date of Publication: May 2008