Post-Copy Live Migration of Virtual Machines

1. Post-Copy Live Migration of Virtual Machines Michael R. Hines, UmeshDeshpande, KartikGopalan Computer Science, Binghamton University(SUNY) SIGOPS 09’

2. Outline • Introduction • Performance Gauge • Design • Evaluation • Conclusion

3. Introduction • Use post-copy live migration • Reduce total migration time and page faults • Implement Dynamic Self Ballooning(DSB) to improve performance of both Pre-copy and Post-copy

4. Performance Gauge(1) • Preparation Time • The time between initiating migration and transferring the VM’s processor states to the target node • Downtime • The time that service on migrated VM is unavailable • Resume Time • The time between resuming the VM’s execution at the target and the end of migration

6. Performance Gauge(2) • Pages Transferred • the total count of memory pages transferred • Total Migration Time • the sum of all the above times from start to finish • Application Degradation • the extent to which migration slows down the applications running in the VM

7. Design(1) -- Approach • 1. Stop the VM on source host • 2. Copy processor state to the target host • 3. Resume the VM on target host • 4. Begin fetching memory pages over the network from the source(Bottleneck) • How to improve?

8. Design(2) • Demand Paging • If VM’s memory accessed result in page fault, that can be serviced by requesting the referenced page over the network from the source node. • ensures that each page is sent over the network only once • Page fault will slow down the VM • Long-term residual dependency

9. Design(3) • Active Push • proactively “push” the VM’s pages from the source to the target even as the VM continues executing at the target • ensures that residual dependencies are removed from the source host as quickly as possible

10. Design(4) • Prepaging • using the faulting addresses as hints to estimate the spatial locality of the VM’s memory access pattern • Bubbling algorithm • Reduce page faults and the duration of the resume phase

11. First , set pivot = 0 Forward Edge of Bubble 0 Max Pivot Forward Edge of Bubble 0 1 0 Max Pivot Page Fault ! Set pivot to the fault page Backward Edge of Bubble Forward Edge of Bubble 0 Max Pivot

13. Design(5) • Dynamic Self-Ballooning (DSB) • Reduce the number of free pages transferred during migration

14. Design(6)—DSB cont. • (1) Inflate the balloon: • A kernel-level DSB thread in the VM first allocates as much free memory as possible and hands those pages over to the hypervisor. • (2) Detect memory pressure: • Memory pressure indicates that some entity needs to access a page frame right away. • The DSB process must partially deflate the balloon depending on the extent of memory pressure. • (3) Deflate the balloon: • Deflation is the reverse of Step 1

15. Evaluation--environment • Host • 2.8 GHz multi-core Intel Machine • Gigabit Ethernet Switch • 4 to 16GB memory • VM • 2 virtual cores • 512MB memory

16. Evaluation(1)—total time

17. Evaluation(2)--downtime

18. Evaluation(3)—pages transferred

20. Conclusion & Comment • Another method for live migration • In some case, it performs better than pre-copy • DSB improve the performance of both pre-copy and post-copy • It’s still unreliable