The Rialto Virtual Memory System

This paper describes the design and implementation of virtual memory in the Rialto kernel. The Rialto VM system supports sparse virtual address spaces with mapping between address spaces, copy-on-write faults, and auto-commit (demand-allocation) faults. It does not currently support demand page-in, page-out, or external pagers. Novel aspects of the design include a VTLB architecture that bounds the memory consumed in machine-dependent mapping structures, real-time requirements for preeemptibility and interruptibility, provision for efficient sharing between user address spaces and the kernel via a user/kernel address bias, and growable kernel-mode thread stacks. The Rialto kernel is a light-weight, “soft” real-time kernel. It has been successfully deployed as part of Microsoft’s MiTV/OS for the set-top boxes in the Microsoft/NTT interactive TV trial in Yokosuka, Japan.