Improving Demand Paging Performance of Compressed Filesystem with NAND Flash Memory

Demand paging with NAND flash memory is an attractive memory management technique for embedded system because of its cost efficiency. However, demand paging has the page fault handling latency. To overcome this drawback, most operating systems take advantage of kernel-level read-ahead. On the contrary, in the compressed filesystem, kernel-level read-ahead degrades performance of demand paging. The main reason is that compressed filesystem has too large read-ahead miss penalty due to decompression overhead. To solve this problem, this paper proposes the conservative read-ahead technique, which improves demand paging performance of compressed filesystem. Proposed technique improves read throughput of device by bulk read from device and reduces decompression overhead of compressed filesystem by selective decompression. We implement conservative read-ahead technique by modifying CramFS and evaluate our implementation in the Linux kernel 2.6.21. Performance evaluation results show that proposed technique reduces the average major page fault handling latency by 28%.