Features/PostCopyLiveMigration

summary

post-copy based live migration

owner

• Name: Dave Gilbert
• Email: dgilbert@redhat.com

description

A postcopy implementation that allows migration of guests that have large page change rates (relative to the avialable bandwidth) to be migrated in a finite time.

design

As much as possible the design attempts to build reusable components that other features can reuse.

This postcopy implementation uses the Linux 'userfault' and 'remap_anon_pages' kernel mechanisms from Andrea Arcangeli; it's not specific to Postcopy and is designed to allow use with all of the standard kernel features (like transparent huge pages, KSM etc).

Mixed pre/post copy is built into the design from the start; a command is sent to switch modes after the migration has been stated (as long as postcopy mode has been enabled first by a capability)

Major components

• 'command' section type for sending migration commands that don't directly reflect guest state; this is used to send messages that move through different phases of postcopy and is expandable for use by others.
• 'return path' a method for the destination to send messages back to the source; used for postcopy page requests, and allows the destination to signal failure back to the source
• 'sent map' a bitmap on the source populated with the set of all pages that have already been transmitted
• 'postcopy pagemap inbound (PMI)' a map on the destination holding the state of each page, whether it's been requested from the source and whether it has been received.

future enhancement

• optimization - rate limit the background page transmission to reduce the impact on the latency of postcopy page requests.
• Integration with RDMA

links

• GitHub repo
• This work is part of the ORBIT project
• Previous postcopy implementation as part of Yabusame