Boosting read-ahead efficiency for improved user experience on mobile devices

Read-ahead schemes of page cache have been widely used to improve read performance of Linux systems. As Android system inherits the Linux kernel, traditional read-ahead schemes are directly applied in mobile devices. However, read request sizes and page cache sizes in mobile devices are much smaller than other platforms, which may decrease read-ahead efficiency and hurt user experience. The read-ahead efficiency is defined as hit pages / all pre-fetched pages in a sequential read. To study the efficiency of traditional read-ahead in mobile devices, this paper first observes that many pre-fetched pages are unused in page cache, which causes high page cache eviction ratio with high extra access latency. Then, this paper analyzes the factors that closely relate to the access latency. It is found that there exists a trade-off between read-ahead size and access latency. A size-tuning scheme is then proposed to explore this trade-off. Experimental results on real mobile devices have shown that the proposed scheme can reduce the number of pre-fetched pages and improve the efficiency of read-ahead without decreasing the page cache hit ratio.