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Live Migration of Virtual Machines. Christopher Clark, Keir Fraser, Steven Hand, Jacob Gorm Hanseny , Eric July, Christian Limpach , Ian Pratt, Andrew Wareld. Index . Motivation Migration Pre-copy migration Challenge in Pre-copy Implementation Managed Migration( Xen )

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live migration of virtual machines

Live Migration of Virtual Machines

Christopher Clark, Keir Fraser, Steven Hand, Jacob GormHanseny,

Eric July, Christian Limpach, Ian Pratt, Andrew Wareld

index
Index
  • Motivation
  • Migration
  • Pre-copy migration
  • Challenge in Pre-copy
  • Implementation
  • Managed Migration(Xen)
  • Self Migration
  • Experiment
  • Optimization
motivation
Motivation
  • Why we need live migration?

We want to move VM without interrupting VM service.

Products:

  • Xen 2.0 : live migration
  • VMware:VMotion
migration
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

migration1
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

challenge in pre copy
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.
implementation
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.
managed migration xen
Managed Migration(Xen)
  • 1st round:
    • Copy all memory pages to destination machine.
    • Replace originalpage 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.
self migration
Self Migration
  • 1st 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.
optimization
Optimization
  • Dynamic Rate-Limiting
  • Rapid Page Dirtying
  • Para-virtualized Optimization

1. Ballooning mechanism

2. Stunning rogue Process