[CRIU] Question : Reduce Snapshot Size

[Pavel Emelyanov]

On 02/17/2016 05:43 PM, Thouraya TH wrote:
> Hi all;
> 
> Please, i have some questions about this case:
> 
> I have three lxc containers in my host. I have done, then, the dumping of these
> three containers. I have, therefore three repository (criu images)
> For my experiments, i have:
> The size of the snapshot is 847M (Mega)
> 
> So, after the dumping process of these three containers, i have three directory
> (images)  of 847M. I'd like to optimise that...
> 
> Mes questions:
> 
> Are these images are identical ? 

Likely they are not. But that's not big deal, since 99% of size sites in
pages-*.img. Those are plain dumps of memory contents, you can compare them
with cmp tool (though this is sub-optimal, see below).

> i think that it depends of the process running
> on each container at the moment of dumping ? that's it ?
> 
> Is there already, a solution to store one snapshot in directory and 2 other directory 
> that contain only the difference ?

We have this possibility when making several subsequent dumps of one container:
https://criu.org/Incremental_dumps

Also there's a actions called "dedup" that evicts duplicate data from pages
images, but again -- it only works for incremental dumps of one container.

If you want to deduplicate data between independent dumps ... well, the code
is there, just need to patch criu to introduce the necessary API and properly
call the existing dedup routines.

-- Pavel