Re: [Xen-devel] Re: how to enable shadow page table? Do I have to run HVM guest systems for shadow paging mode?

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 17:57 +0000 on 16 Mar (1237226223), Dan Magenheimer wrote:
> For the record, Transcendent Memory is not a copy-on-write
> mechanism, doesn't deal with shadow tables or PTE read/write
> bits, and is really not exotic at all.

Indeed.  I was just including it in the current bundle of "fun things
to do with memory management". :)  And since it helps with systems under
memory pressure it might have solved whatever the underlying problem was.
Almost nobody wants to write a copy-on-write mechanism just for the
beauty of the thing.

Cheers,

Tim.

>  It's a simple (though
> paravirtualized) mechanism for optimizing the usage of
> unutilized or underutilized physical memory while ensuring
> (most of) that memory is synchronously reclaimable for
> unexpectedly urgent needs.  :-)
> 
> Dan
> 
> > -----Original Message-----
> > From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx]
> > Sent: Monday, March 16, 2009 11:41 AM
> > To: Jeremy Fitzhardinge
> > Cc: Xen-devel; Long Wang
> > Subject: [Xen-devel] Re: how to enable shadow page table? Do I have to
> > run HVM guest systems for shadow paging mode?
> > 
> > 
> > At 16:30 +0000 on 16 Mar (1237221012), Jeremy Fitzhardinge wrote:
> > > Long Wang wrote:
> > > > I am working on a research project based on Xen 3.3.1. I 
> > want to use the
> > > > shadow page table for setting guest system memory pages 
> > as read-only and/or
> > > > dirty, and perform a copy-on-write mechanism when these 
> > memory pages are
> > > > updated.
> > 
> > Several people are already working on copy-on-write memory in Xen, or
> > variations on that theme (Mike Sun, Patrick Colp, John Byrne, and
> > others) as well as more exotic things like Difference Engine and
> > Transcendent Memory.  It would probably be better to talk to those
> > people and try to help their efforts than start from scratch.
> > 
> > Patrick Colp's slides from the most recent Xen Summit give an idea of
> > one method of implementing it:
> > http://www.xen.org/files/xensummit_oracle09/VMSnapshots.pdf
> > 
> > Cheers,
> > 
> > Tim.
> > 
> > -- 
> > Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> > Principal Software Engineer, Citrix Systems (R&D) Ltd.
> > [Company #02300071, SL9 0DZ, UK.]
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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