Storage Type and Hot Partition Aware Page Reclamation for NVM Swap in Smartphones

With the rapid advances in mobile app technologies, new activities using smartphones emerge every day including social network and location-based services. However, smartphones ex-perience problems in handling high priority tasks, and often close apps without the user’s agreement when there is no available memory space. To cope with this situation, supporting swap with fast NVM storage has been suggested. Although swap in smartphones incurs serious slowing-down problems in I/O operations during saving and restoring the context of apps, NVM has been shown to resolve this problem due to its fast I/O features. Unlike previous studies that only focused on the management of NVM swap itself, this article discusses how the memory management system of smartphones can be further improved with NVM swap. Specifically, we design a new page reclamation algorithm for smartphone memory systems, which considers the following: (1) storage types of each partition (i.e., file system for flash storage and swap for NVM), and (2) access hotness of each partition including operation types and workload characteristics. By considering asymmetric I/O cost and access density for each partition, our algorithm improves the I/O performance of smartphones significantly. Specifically, it improves the I/O time by 15.0% on average and by up to 35.1% compared to the well-known CLOCK algorithm.