Large-reach memory management unit caches

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Abstract
Within the ever-important memory hierarchy, little research is devoted to Memory Management Unit (MMU) caches, implemented in modern processors to accelerate Translation Lookaside Buffer (TLB) misses. MMU caches play a critical role in determining system performance. This paper presents a measurement study quantifying the size of that role, and describes two novel optimizations to improve the performance of this structure on a range of sequential and parallel big-data workloads. The first is a software/hardware optimization that requires modest operating system (OS) and hardware support. In this approach, the OS allocates page table pages in ways that make them amenable for coalescing in MMU caches, increasing their hit rates. The second is a readily-implementable hardware-only approach, replacing standard per-core MMU caches with a single shared MMU cache of the same total area. Despite its additional access latencies, reduced miss rates greatly improve performance. The approaches are orthogonal; together, they achieve performance close to ideal MMU caches. Overall, this paper addresses the paucity of research on MMU caches. Our insights will assist the development of high-performance address translation support for systems running big-data applications.