Re: migrate_set_downtime bug

[Glauber Costa <glommer@redhat.com>]

On Wed, Sep 30, 2009 at 04:11:32PM +0200, Dietmar Maurer wrote:
> > On Wed, Sep 30, 2009 at 10:55:24AM +0200, Dietmar Maurer wrote:
> > > Another problem occur when max_downtime is too short. This can
> > results in never ending migration task.
> > >
> > > To reproduce just play a video inside a VM and set max_downtime to
> > 30ns
> > >
> > > Sure, one can argument that this behavior is expected.
> > >
> > > But the following would avoid the problem:
> > >
> > > +    if ((stage == 2) && (bytes_transferred > 2*ram_bytes_total())) {
> > > +        return 1;
> > > +    }
> > why 2 * ?
> > This means we'll have to transfer the whole contents of RAM at least
> > twice to hit this condition, right?
> 
> Yes, this is just an arbitrary limit. 
I don't know. If we are going for a limit, I would prefere a limit of pages yet to transfer,
not pages already transferred.

However, the very reason this whole thing was written in the first place, was to leave choices
to management tools ontop of qemu, not qemu itself. So I would say yes, if you set limit for 30ns,
you asked for it never finishing.

Your first patch is okay, tough.