A Hybrid Swapping Scheme Based On Per-Process Reclaim for Performance Improvement of Android Smartphones (August 2018)

As a way to increase the actual main memory capacity of Android smartphones, most of them make use of zRAM swapping, but it has limitation in increasing its capacity since it utilizes main memory. Unfortunately, they cannot use secondary storage as a swap space due to the long response time and wear-out problem. In this paper, we propose a hybrid swapping scheme based on per-process reclaim that supports both secondary-storage swapping and zRAM swapping. It attempts to swap out all the pages in the working set of a process to a zRAM swap space rather than killing the process selected by a low-memory killer, and to swap out the least recently used pages into a secondary storage swap space. The main reason being is that frequently swapin/out pages use the zRAM swap space while less frequently swap-in/out pages use the secondary storage swap space, in order to reduce the page operation cost. Our scheme resolves both the response time and wear-out problems of secondary-storage swapping and zSWAP, and overcomes the size limitation of the zRAM swap space. According to performance measurements, it also increased the extension ratio of main memory by 15 17% and 6 17% and reduced the page operation cost by 9 22% and 18 28%, respectively, compared with zRAM swapping and zSWAP.