Fix Page Fault in Post-Copy Live Migration with RemotePF Page Table Assistant

Abstract

While using post-copy algorithm for virtual machine (VM) live migration, guest operating system access to a not-yet-transferred memory page will cause a page fault(PF). Destination host should send page request to source host to get the missing page. If the VM is not being migrated, Xen hypervisor will fix the PF by itself. But, the page fault information does not contain the VM's migration status. So, Xen has to deliver all the page faults, to an independent page fault handler unit, whether it is caused by post-copy live migration or not. Let the monitor do the judgment and make decision. This will reduce the VM performance especially while the VM at non-migration status. In this paper, we design and implement a new Xen page table assistant named as RemotePF(Remote Page Fault). RemotePF is used to identify the VM migration status. So, Xen could skip the page fault handle unit and get the VM migration status directly from RemotePF. We implemented the post-copy live migration algorithm and RemotePF page table assistant (PTA) for Xen. The experimental results show that RemotePF can accurately identify the VM migration status, reduce page faults fixing time, and has little influence on the normal running VM.