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Re: [Qemu-devel] [PATCH v4 42/47] Don't sync dirty bitmaps in postcopy
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v4 42/47] Don't sync dirty bitmaps in postcopy |
Date: |
Tue, 25 Nov 2014 16:25:58 +0000 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* 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