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[[Category:Plans]]
== Overview ==
[[Category:Empty articles]]
Lazy, or [[wikipedia:Live_migration#Post-copy_memory_migration|post-copy memory migration]], allows to minimize application downtime. Unlike [[wikipedia:Live_migration#Pre-copy_memory_migration|pre-copy memory migration]], lazy migration does not copy the task's memory, but rather keeps the memory pages at the source node. Only the minimal task state required to start the application is copied to the destination node and the task is resumed there. When the task accesses missing memory pages, <code>criu</code> processes the page faults, transfers the required page from the source node and injects it into the running task address space.
== Using Lazy Migration ==
=== Dump ===
The <code>dump</code> action should be invoked with <code>--lazy-pages</code> option. In addition, <code>--address</code> and <code>--port</code> options may be used to select IP address and port that will be serving the page requests
[src]# criu dump --tree <pid> --images-dir <dir> --lazy-pages --address <src> --port <port>
=== Copy images ===
Copy the images onto the destination node:
[src]# scp -r <dir> <dst-node>/<dir>
The images do not contain the massive bulk of the memory dump, they are relatively small and the copy won't take long.
=== Lazy-pages Daemon ===
The <code>lazy-pages</code> daemon is responsible for handling the task's page faults and injecting the memory pages into the task's address space. The <code>--page-server</code> option should be set so that <code>lazy-pages</code> daemon will connect to the '''src''' node. The <code>--address</code> and <code>--port</code> options should be used to define the IP address and port of the <code>dump</code> side.
[dst]# criu lazy-pages --page-server --address <src> --port <port>
=== Restore ===
The <code>restore</code> should be run with <code>--lazy-pages</code> option
[dst]# criu restore --images-dir <dir> --lazy-pages
Note, that <code>lazy-pages</code> and <code>restore</code> must be run in the same working directory, or <code>--work-dir</code> option should be explicitly set.
== See also ==
* [[Userfaultfd]]
* [[Live migration]]
* [[Iterative migration]]
[[Category:Develpment]]
[[Category:Live migration]]
[[Category:Live migration]]