REMOCA: Hypervisor Remote Disk Cache

In virtual machine (VM) systems, with the increase in the number of VMs and the demands of applications, the main memory is becoming a bottleneck of application performance. To improve paging performance for memory-intensive or I/O-intensive workloads, we propose the hypervisor REMOte disk CAche (REMOCA), which allows a virtual machine to use the memory resources on other physical machines as its cache between its virtual memory and virtual disk devices. The goal of REMOCA is to reduce disk accesses, which is much slower than transferring memory pages over modern interconnect networks. As a result, the average disk I/O latency can be improved. REMOCA is implemented within the hypervisor, by intercepting guest events such as page evictions and disk accesses. This design is transparent to the applications, and is compatible with existing techniques like ballooning and ghost buffer. Moreover, a combination of them can provide a more flexible resource management policy. Our experimental results show that REMOCA can efficiently alleviate the impact of thrashing behavior, and also significantly improve the performance for real-world I/O intensive applications.