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Re: [Xen-devel] Fast checkpoints with COW VM memory

To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Fast checkpoints with COW VM memory
From: "Mike Sun" <msun@xxxxxxxxxx>
Date: Mon, 4 Feb 2008 22:14:26 -0500
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Hi --

I'm attempting to implement some sort of COW functionality for use in
fast snapshotting, but have a few questions I'm hoping people can help
out with.

As per typical OS COW implementations, I mark the memory pages I want
COW to read only protection.  When I receive the page protection fault
in the hypervisor page fault handler, is there a way for me to
determine if the protection fault is the result my my COW action as
opposed to a protection fault actually incurred by the guest (i.e.
perhaps the guest OS is implementing its own COW on portions of its
memory)?  The only method I can think of is to keep track of the
protection bits of the pages before I have the hypervisor modify them
to read only, and use this information in the hypervisor's page fault
handler to determine what it should reset the page's protection bits
to be after the page has been copied.


2008/1/15 Mike Sun <msun@xxxxxxxxxx>:
> Hi --
> I'm currently in the process of implementing the COW functionality.
> It will probably take me some time, but I'll get back to you when I
> have a better idea of what the timeline will be.
> Mike
> On Jan 15, 2008 10:23 PM, tgh <wwwwww4187@xxxxxxxxxxx> wrote:
> > hi
> > I am interested in the COW VM memory ,and are there some code or patch
> > about it ,or still in process ,or in plan? and if it has been
> > implemented and integrated in the source tree, then ,what is the way to
> > use it ? say , fast checkpoint, or VM fork ?or something else? is it
> > available to use ? or how to do it ?
> >
> > Thanks
> >
> >
> >
> >
> > Tim Deegan 写道:
> >
> > > At 14:59 -0500 on 05 Dec (1196866790), Mike Sun wrote:
> > >
> > >> According to the Xen Roadmap for 2006, there was talk of copy-on-write
> > >> functionality that could be developed easily from the
> > >> save/restore/migration code to enable features such as fast
> > >> checkpoints or even VM forks.
> > >>
> > >
> > > FSVO "easily". :)  I am working on extending the typed P2M work I did a
> > > while ago to allow pages to be marked copy-on-write, and other similar
> > > memory tricks.  It's still in the planning stage, but I hope to have
> > > some patches for comment fairly soon.
> > >
> > > Brendan Cully gave a talk on this area at the last Summit, and I know
> > > there is more work going on at UBC too.
> > >
> > > Tim
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