Maintaining Application Context of Smartphones by Selectively Supporting Swap and Kill

With the rapid diffusion of smartphones as well as the technical advances in mobile platform technologies, application domains supported by smartphones have dramatically increased. Unlike traditional computer systems, however, the context of applications may be lost in a smartphone as mobile OS usually kills applications without user's approval when free memory space is exhausted. This was not a serious issue when a smartphone was a personal entertainment device, but it is now significant as a lot of official works are also performed by a smartphone. Instead of killing a process, the context of an application can be backed up to swap storage, but smartphones do not accept it as swap incurs excessively heavy I/O traffic. However, our findings show that the overhead of swap is not serious in recent smartphone devices and it can also be eliminated by judicious software management. This article proposes a selective swap scheme that classifies applications based on their context-saving characteristics, and controls the number of processes involved in swap by monitoring system situations and application characteristics. That is, we maintain the context of applications selectively by swap or application's own state-saving. We implement and measure the effectiveness of our scheme on a real Android device, showing that it provides the context-savings of applications without additional overhead.