Incremental dumps

FIXME: describe why incr. dumps are needed, and when to use pre-dump (iterative migration) instead of incr. dumps.

If you're doing several dumps in a row, the 2nd and subsequent dumps can be sped up. Here's how:

Create the first dumpEdit

# mkdir -p <path-to-images>/1/
# criu dump --tree <pid> --images-dir <path-to-images>/1/ --leave-running --track-mem

Images are put into the 1/ sub-directory, since we're about to create the 2nd (and more) incremental dumps and it's handy to store them in this way;
The --leave-running option is used to make criu not kill the tasks after dump, but let them run further;
The --track-mem option makes criu ask kernel to monitor memory changes to optimize the subsequent dump.

Create the second dumpEdit

# mkdir <path-to-images>/2/
# criu dump --tree <pid> --images-dir <path-to-images>/2/ --leave-running --track-mem --prev-images-dir ../1/

Note, that the --prev-images-dir path is relative to the --images-dir one;
Similarly the 3rd and all the other dumps can be created.

Create the last dumpEdit

# mkdir <path-to-images>/N/
# criu dump --tree <pid> --images-dir <path-to-images>/N/ --track-mem --prev-images-dir ../N-1/

No --leave-running option will make tasks be killed after dump;
No need in memory tracking option.

RestoreEdit

Now you can restore the processes from whatever images you want

# criu restore --images-dir <path-to-images>/ANY/

Note: After each (but the last) dump tasks continue running and thus can modify filesystem. CRIU does not snapshot filesystem and assumes, that proper filesystem state for restore is provided by a user.

Data deduplicationEdit

See memory images deduplication.