Non-Volatile Memory Based Page Swapping for Building High-Performance Mobile Devices

Smartphones are getting increasingly high-performance with advances in mobile processors and larger main memories to support feature-rich applications. However, the storage subsystem has always been a prohibitive factor that slows down the pace of reaching even higher performance while maintaining good user experience. Despite today's smartphones are equipped with larger-than-ever main memories, they consume more energy and still run out of memory. But the slow NAND flash based storage vetoes the possibility of swapping-an important technique to extend main memory-and leaves a system that constantly terminates user applications under memory pressure. In this paper, we propose NVM-Swap by revisiting swapping for smartphones with fast, byte-addressable, non-volatile memory (NVM) technologies. Instead of using flash, we build the swap area with NVM, to allow high performance without sacrificing user experience. NVM-Swap supports Lazy Swap-in, which can reduce memory copy operations by giving the swapped out pages a second chance to stay in byte-addressable NVM backed swap area. To avoid fast worn-out of certain NVM, we also propose Heap-Wear, a wear leveling algorithm that distributes writes in NVM more evenly. Evaluation results based on the Google Nexus 5 smartphone show that our solution can effectively enhance smartphone performance and achieve better wear-leveling of NVM.