SwapX: An NVM-Based Hierarchical Swapping Framework

Non-volatile memory (NVM) provides persistence with dynamic random access memory (DRAM)-like performance. This paper presents SwapX, an NVM-based hierarchical swapping framework for guest operating systems (OSs) in virtual machines (VMs). SwapX works in a cluster connected to a NVM pool, where each server is equipped with both NVM and DRAM to provide hierarchical swapping service for VMs. SwapX: 1) manages free NVM on different machines and forward swap request to the central NVM pool and 2) adaptively maps the virtual address space of VMs onto the hosts DRAM, NVM, and the NVM pool according to its access patterns, so that the guest pages could be transparently swapped to the appropriate place. Prototype evaluation shows that SwapX improves energy efficiency significantly compared with both DRAM-swap and local disk swap, and only introduces small performance loss compared with DRAM-swap.