1. Live Migration of Virtual Machines
Christopher Clark, Keir Fraser, Steven Hand, Jacob Gorm Hanseny,
Eric July, Christian Limpach, Ian Pratt, Andrew Wareld

2. Index Motivation Migration Pre-copy migration Challenge in Pre-copy
Implementation
Managed Migration(Xen)
Self Migration
Experiment
Optimization

3. Motivation Why we need live migration?
We want to move VM without interrupting VM service.
Products:
Xen 2.0 : live migration
VMware:VMotion

4. Migration Two important consideration: 1. Downtime
2. Total migration time
All migrations mechanism can be divided into three phases.
1. Push phase
2. Stop-and-copy phase
3. Pull phase

5. Migration Example: Stop-and-copy => Only stop-and-copy phase
Pure demand-migration
=> Stop-and-copy phase and Pull phase
Pre-copy
=> Push phase and Stop-and-copy phase

6. Pre-copy migration

7. Challenge in Pre-copy
Every VM have some set of pages which updates very frequently.
And the Sets size would influence downtime of the migration.
Writable Working Sets
The bandwidth of network also impact the migration time.

8. Implementation There are two kinds of implementation of migration.
Managed Migration
The physical machine has a management VM. (Xen)
Self Migration
There are three conditions to change into stop-and-copy phase.
The dirty rate is bigger than the upper bound.
The size if working set is small enough.
The limit of the rounds.

9. Managed Migration(Xen)
1st round:
Copy all memory pages to destination machine.
Replace original page table with shadow page table whose all pages are marked read-only .
Create a dirty bit map for the VM.
2nd-(n-1)th round:
During the pages transferring, if VM want to modify a page, it will invoke Xen to set the appropriate bit in the dirty bit map.
Dirty pages will be resend again.
Reset dirty bit map for the next round.
nth round:
When the Dirty rate is bigger than up bound, begin to do stop-and-copy.

10. Self Migration 1st round: 2nd-(n-1)th round: nth round:
Copy all memory pages to destination machine.
Mark all virtual address as write-protect.
The OS create a dirty bit map(used to tracking physical pages) to memory the modified pages.
2nd-(n-1)th round:
During the pages transferring, if write faults occur, OS will set the appropriate bit in the dirty map.
Dirty pages will resend again.
Reset dirty bit map for the next round.
nth round:
When the dirty rate is bigger than the upper bound, OS would disable all activities.
Copy all dirty pages to shadow buffer.
Transfer the buffer and ignore new page updates.

11. Web Server migration

12. SPECweb99 benchmark

14. A worst case example

15. Optimization Dynamic Rate-Limiting Rapid Page Dirtying
Para-virtualized Optimization
1. Ballooning mechanism
2. Stunning rogue Process