[CRIU] Lazy-restore design discussion - round 2

[Adrian Reber]

On Mon, Apr 18, 2016 at 02:13:47PM +0300, Mike Rapoport wrote:
> On Mon, Apr 18, 2016 at 12:47:00PM +0200, Adrian Reber wrote:
> > On Mon, Apr 18, 2016 at 01:10:05PM +0300, Mike Rapoport wrote:
> > > On Mon, Apr 18, 2016 at 12:31:14PM +0300, Pavel Emelyanov wrote:
> > > > On 04/18/2016 10:46 AM, Adrian Reber wrote:
> > > > > It seems we have reached some kind of agreement and therefore
> > > > > I am trying to summarize, from my point of view, our current discussion
> > > > > results.
> > > > 
> > > > Thanks for keeping track of this :)
> > > 
> > > Adrian, you've beat me on this :)
> > >  
> > > > >  * The UFFD daemon does not need a checkpoint directory to run, all
> > > > >    required information will be transferred over the network.
> > > > >    e.g. PID and pages
> > > > 
> > > > I would still read process tree from images dir.
> > > 
> > > +1
> > 
> > Hmm, then I don't get it how the patches "lazy-pages: handle multiple
> > processes" fit into it. How can the uffd daemon handle multiple restore
> > requests when it needs to know where the checkpoint directory is? As I
> > understand it I can either start it without '-D' and it gets the
> > information about the pagemap-s from somewhere else (the network) or I
> > can start the uffd daemon with '-D', but why should it then handle
> > multiple requests as all the required information is in a directory
> > specified on the command-line, which can change for every restored
> > process. From my point of view this seems contradictory.
> 
> I think we have huge misunderstanding between us here. My view was that
> uffd daemon behaves somewhat similar to page-server daemon. It is launched
> with -D, waits for restore to get the uffd's and then handles #PF's that
> come from the processes being restored. To take care of a #PF, uffd-daemon
> either reads pages*.img from the checkpoint directory or gets the pages
> from the dump side over the network.
> 
> In my understating "multiple requests" means that single uffd-daemon takes
> care of the entire process tree present in the checkpoint directory...

Thanks. Finally I understood it. Now it makes more sense.

		Adrian