Maintaining Application Context of Smartphones by Selectively Supporting Swap and Kill

Abstract

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.

Mobile Memory Management System Based on User’s Application Usage Patterns

“…In a study using ZRAM and storage as the swap area [17], the swap cost of a page was calculated to swap out frequently referenced pages into ZRAM while swapping out infrequently used pages to storage. Taking compression ratio [18] or application behavior [19] into consideration to estimate the cost of a page showed benefits for swapping out pages, extended storage lifespan and higher application launch speeds. In a study that proposed memory management using the average reuse distance [10,14], which indicates the number of times other applications were launched between the launch and relaunch of an application, it was considered that an application was more likely to be relaunched when its average reuse distance was smaller.…”

“…This prevents users from experiencing reduced system performance when they relaunch frequently used applications. Swap techniques that use secondary storage as part of the main memory space have been considered [4][5][6] to efficiently utilize the main memory of smartphones. However, owing to wear-out problems of NAND flash memory-based storage devices, ZRAM [7], which compresses memory space and uses it as swap space, or ZSWAP [8], which is used as swap cache, can be used for smartphone memory management.…”

Characterization of Android Memory References and Implication to Hybrid Memory Management

“…When free memory space is below the LMK-threshold, Android triggers LMK to make free memory. LMK selects the lowest priority application and kills it, thereby freeing all pages belonging to that application [41]. The priorities of applications are determined based on the time of the last use.…”

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

“…This can be realized by memory swap, which makes use of secondary storage as an extension of the main memory to save the context of an app when free memory space is not sufficient [8]. Even if swap has been widely adopted in existing computer systems, it is not easy to support swap in smartphones [7,9]. In particular, a serious slowing-down problem during launching an app is observable with a smartphone that activates the swap function [7].…”