Memory images deduplication
When performing incremental dumps or iterative migration, a layered stack of memory images is created. In that stack, some data is duplicated (i.e. same memory page is present in multiple images). This article describes ways to deduplicate such data by punching holes in image files (using fallocate() syscall with FALLOC_FL_PUNCH_HOLE flag), effectively freeing used disk space.
Two ways to deduplicate memory images are available.
Deduplication action
The criu dedup command opens the image directory and punches holes in the parent images where child images would replace them.
On the fly deduplication
The --auto-dedup option can be used for criu dump and criu page-server. It causes every write to images with process' pages to punch holes in the respective parent images.
The option is extremely useful in disk-less migration scenario.