Radixvm: scalable address spaces for multithreaded applications

RadixVM is a new virtual memory system design that en-ables fully concurrent operations on shared address spaces for multithreaded processes on cache-coherent multicore com-puters. Today, most operating systems serialize operations such as mmap and munmap, which forces application de-velopers to split their multithreaded applications into multi-process applications, hoard memory to avoid the overhead of returning it, and so on. RadixVM removes this burden from application developers by ensuring that address space operations on non-overlapping memory regions scale per-fectly. It does so by combining three techniques: 1) it orga-nizes metadata in a radix tree instead of a balanced tree to avoid unnecessary cache line movement; 2) it uses a novel memory-efficient distributed reference counting scheme; and 3) it uses a new scheme to target remote TLB shootdowns and to often avoid them altogether. Experiments on an 80 core machine show that RadixVM achieves perfect scalability for non-overlapping regions: if several threads mmap or munmap pages in parallel, they can run completely independently and induce no cache coherence traffic.