DaaC: device-reserved memory as an eviction-based file cache

Most embedded systems require contiguous memory space to be reserved for each device, which may lead to memory under-utilization. Although several approaches have been proposed to address this issue, they have limitations of either inefficient memory usage or long latency for switching the reserved memory space between a device and general-purpose uses. Our scheme utilizes the reserved memory as an eviction-based file cache. It guarantees contiguous memory allocation to devices while providing idle device memory as an additional file cache called eCache for general-purpose usage. Since the eCache stores only evicted data from in-kernel page cache, memory efficiency is preserved and allocation time for devices is minimized. Cost-based region selection also alleviates additional read I/Os by carefully discarding cached data from the eCache. The prototype is implemented on the Nexus S smartphone and is evaluated with popular Android applications. The evaluation results show that 50%-85% of flash read I/Os are reduced and application launch performance is improved by 8%-16% while the reallocation time is limited to a few milliseconds.