Exploiting Sub-page Write Protection for VM Live Migration

Virtual machine (VM) live migration is an essential feature for cloud vendors. Since VM live migration involves transferring a large amount of memory between VMs, reducing memory transfer is critical to successful and efficient migration. However, software-based approaches consume considerable CPU and memory resources, resulting in degraded performance under heavy load. We propose to exploit a new CPU feature, sub-page write protection, to reduce memory transfer in VM live migration. To mitigate the overhead in naive implementations, we identified its leading cause and introduced an optimization. Emulator-based experiments demonstrated that our approach reduced memory transfer as much as software-based approaches while consuming less CPU and memory. Our optimization reduced the maximum CPU overhead by 25.5 percentage points.