Architectural Support For Translation Table Management In Large Address Space Machines

Abstract

Virtual memory page translation tables provide mappings from virtual to physical addresses. When the hardware controlled Translation Lookaside Buffers (TLBs) do not contain a translation, these tables provide the translation. Approaches to the structure and management of these tables vary from full hardware implementations to complete software based algorithms. The size of the virtual address space used by processes is rapidly growing beyond 32 bits of address. As the utilized address space increases, new problems and issues surface. Traditional methods for managing the page translation tables are inappropriate for large address space architectures. The Hashed Page Table (HPT), described here, provides a very fast and space efficient translation table that reduces overhead by splitting TLB management responsibilities between hardware and software. Measurements demonstrate its applicability to a diverse range of operating systems and workloads and, in particular, to large virtual address space machines. In simulations of over 4 billion instructions, improvement of 5 to 10% were observed.