Post-Copy Live Migration of Virtual Machines
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Post-Copy Live Migration of Virtual Machines
Michael R. Hines, Umesh Deshpande, Kartik GopalanComputer Science, Binghamton University(SUNY)
SIGOPS 09’
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Outline
• Introduction• Performance Gauge• Design• Evaluation• Conclusion
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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
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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
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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
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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?
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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
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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
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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
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First , set pivot = 0
0 Max
Pivot
Forward Edge of Bubble
0 Max
Pivot
1 0 Forward Edge of Bubble
0 Max
Pivot
Page Fault ! Set pivot to the fault page
Forward Edge of Bubble Backward Edge of Bubble
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Design(5)
• Dynamic Self-Ballooning (DSB)– Reduce the number of free pages transferred
during migration
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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
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Evaluation--environment
• Host– 2.8 GHz multi-core Intel Machine– Gigabit Ethernet Switch– 4 to 16GB memory
• VM– 2 virtual cores– 512MB memory
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Evaluation(1)—total time
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Evaluation(2)--downtime
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Evaluation(3)—pages transferred
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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