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

Outline Introduction Performance Gauge Design Evaluation Conclusion 2

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 3

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 4

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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 6

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? 7

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 8

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 9

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 10

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

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

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 14

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

Evaluation(1)—total time 16

Evaluation(2)--downtime 17

Evaluation(3)—pages transferred 18

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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 20