Lazy, or post-copy memory migration, allows to minimize application downtime. Unlike 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,
criu 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 action should be invoked with
--lazy-pages option. In addition,
--port 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 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 is responsible for handling the task's page faults and injecting the memory pages into the task's address space. The
--page-server option should be set so that
lazy-pages daemon will connect to the src node. The
--port options should be used to define the IP address and port of the
[dst]# criu lazy-pages --page-server --address <src> --port <port>
restore should be run with
[dst]# criu restore --images-dir <dir> --lazy-pages
restore must be run in the same working directory, or
--work-dir option should be explicitly set.
To view an example video of using a lazy-pages, please go to https://asciinema.org/a/146427.