Re: [Qemu-devel] [PATCH v4 42/47] Don't sync dirty bitmaps in postcopy

[Dr. David Alan Gilbert]

* David Gibson (address@hidden) wrote:
> On Fri, Oct 03, 2014 at 06:47:48PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > Once we're in postcopy the source processors are stopped and memory
> > shouldn't change any more, so there's no need to look at the dirty
> > map.
> > 
> > There are two notes to this:
> >   1) If we do resync and a page had changed then the page would get
> >      sent again, which the destination wouldn't allow (since it might
> >      have also modified the page)
> >   2) Before disabling this I'd seen very rare cases where a page had been
> >      marked dirtied although the memory contents are apparently identical
> 
> It would be nice to understand how that happened.

Yes, I'd come to the conclusion it was a device that was prodding about in user
memory space even though it should have stopped, although I hadn't gone and
traced them down.

Dave

> 
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> 
> Otherwise,
> 
> Reviewed-by: David Gibson <address@hidden>
> 
> -- 
> David Gibson                  | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au        | minimalist, thank you.  NOT _the_ 
> _other_
>                               | _way_ _around_!
> http://www.ozlabs.org/~dgibson


--
Dr. David Alan Gilbert / address@hidden / Manchester, UK