How to Use a 64-Bit Virtual Address Space

Most operating systems execute programs in private address spaces communicating through messages or les. The traditional private address space model was developed for 16and 32-bit architectures, on which virtual addresses are a scarce resource. The recent appearance of architectures with at 64-bit virtual addressing opens an opportunity to reconsider our use of virtual address spaces. In this paper we argue for an alternative addressing model, in which all programs and data reside in a single global virtual address space shared by multiple protection domains. Hardware-based memory protection exists within the single address space, providing rewalls as strong as in conventional systems. We explore the tradeo s in the use of a global virtual address space relative to the private address space model. We contend that a shared address space can eliminate obstacles to e cient sharing and exchange of data structures that are inherent in private address space systems. The shared address space o ers advantages similar to some capability-based computer systems, but can be implemented on standard page-based hardware, without the performance costs and restricted data model typical of capability-based systems. We introduce Opal, an operating system to support this model on paged 64-bit architectures. The key feature of Opal is a at virtual address space that includes data on long-term storage and across the network.