[CRIU] criu and userfaultfd

[Adrian Reber]

On Wed, Sep 02, 2015 at 03:23:47PM +0300, Pavel Emelyanov wrote:
> On 09/01/2015 06:22 PM, Adrian Reber wrote:
> > As userfaultfd has been mentioned multiple times at Linux Plumbers
> > Conference I wanted to ask if anybody already has some code in that
> > direction?
> 
> Sanidhya (in Cc) should have played with it for a while. Also I had
> some kernel work to make userfaultfd support CRIU case, it can be
> found here [1]. I planned to get back to them once Andrea's work gets
> merged into the upstream.

Ah, interesting. I have also looked into userfaultfd and have now a
simple test case where I have two processes exchanging FDs. One process
tries to access memory which is handled by userfaultfd and hanging until
I make the memory area available from the other process using
userfaultfd.

Trying to understand what would be necessary to use userfaultfd with
CRIU I would expect to restore everything except the memory pages using
CRIU and marking all to the process related pages as being handled by
userfaultfd. For each non existing page a request should be handled by
userfaultfd. 

Are there any other problems which need to be resolved to restore
processes in combination with userfaultfd? I would like to try it out
and just want to make sure this is not completely impossible.

		Adrian