DeVAS: Decoupled Virtual Address Spaces

The constant growth of workload size in modern applications is making address translation a performance bottleneck. In principle, increasing the virtual page size could be advantageous, as it would allow each cached address translation to cover a larger memory space. Nevertheless, the utilization of larger pages introduces challenges, such as issues related to memory fragmentation and physical page management. In this paper, we present Decoupled Virtual Address Spaces (DeVAS), a virtual memory proposal that enables the decoupling of address translation and memory allocation, by allowing different sizes for virtual and physical pages, aiming to exploit the benefits of both. DeVAS introduces an intermediate virtual address space allocated by the Operating System employing larger pages (e.g., 2MiB), corresponding to the virtual page size seen by the processor, and a memory controller extension devoted to their allocation in physical memory at a smaller granularity (e.g., 4KiB). We show that DeVAS achieves an average 1.13 × performance improvement over a traditional configuration (i.e., with 4KiB pages) with no specific architectural modifications and for memory-intensive benchmarks. Moreover, DeVAS strategy enables architectural modifications for increasing performance, such as simplified/optimized TLB structure and L1-cache design flexibility. When considering these adjustments, DeVAS achieves a speedup of up to 1.20 × compared to the same reference. Furthermore, it matches and even edges the performance of an ideal (i.e., not implementable in practice) virtual memory configuration based on 2MiB pages only.