Shared-Page Management for Improving the Temporal Isolation of Memory Reservations in Resource Kernels

Memory reservation provides real-time applications with guaranteed memory access to a specified amount of physical memory. However, previous work on memory reservation primarily focused on private pages, and did not pay attention to shared pages, which are widely used in current operating systems. With previous schemes, a real-time application may experience unexpected timing delays from other applications through shared pages that are shared by another process, even though the application has enough free pages in its reservation. In this paper, we describe problems with shared pages in real-time applications, and propose a shared-page management mechanism to enhance the temporal isolation of memory reservations in resource kernels that use resource reservation. The proposed mechanism consists of two techniques, Shared-Page Conservation (SPC) and Shared-Page Eviction Lock (SPEL), each of which prevents timing penalties caused by the seemingly arbitrary eviction of shared pages. The mechanism can manage shared data for inter-process communication and shared libraries, as well as pages shared by the kernel´s copy-on-write technique and file caches. We have implemented and evaluated our schemes on the Linux/RK platform, but it can be applied to other operating systems with paged virtual memory.