Rental memory management for embedded systems

Abstract

Memory reservation in embedded systems is a prevalent approach to provide a physically contiguous memory region to its acceleration devices, such as a camera device and a video decoder. Inefficiency of the memory reservation becomes a more significant problem in emerging embedded systems, such as smartphones and smart TVs. Many ways of using the systems increase the idle time of their integrated devices, and eventually decrease the utilization of their reserved memory. Firstly, this dissertation proposes a rental memory management scheme to minimize the memory inefficiency caused by the memory reservation. The memory space reserved for a device can be rented for other purposes when the device is not active. For this scheme to be viable, latencies associated with reallocating the memory space should be minimal. Volatile pages are good candidates for such page reallocation since they can be reclaimed immediately as the original device needs them. We implemented our scheme on a smartphone development board with the Android Linux kernel. Our prototype has shown that the time for the return operation is less than 0.3 seconds in the tested cases. We believe that this time is acceptable to end-users in terms of transparency since the time can be hidden in application initialization time. The rental memory also brings throughput increases by from 2% to 200% based on the available memory and the applications’ memory intensiveness. Secondly, this dissertation proposes an eviction-based rental memory management scheme. This scheme complements the first scheme in terms of the memory efficiency and the high unit cost of the reallocation. To this end, this scheme uses the rental memory as a secondary file cache called eCache. The eCache provides contiguous reallocation for devices and secondary caching for system performance. Since the eCache stores only evicted data from in-kernel page cache, memory efficiency is preserved and allocation time for devices is greatly minimiz...