[Tmem-devel] Implementing Transcendent Memory on Lguest

[Dan Magenheimer]

Hi Nitin --

Nice!  I have been out of the office most of the last month so
am still getting unburied. :-(

Again admitting ignorance of virtio, I have two concerns, performance
and coherence, both assuming that there is some temporary storage
of the tmem data (e.g. in a "ring buffer" or equivalent).  Is
there any such temporary storage, or does the data always get
transferred directly to the hypervisor?

For example, for performance, a ring buffer would be an extra page
copy; for coherence, data stored in a ring buffer might not get
flushed by a tmem flush command.

Thanks,
Dan

> -----Original Message-----
> From: Nitin Gupta [mailto:ngupta at vflare.org]
> Sent: Monday, February 08, 2010 11:04 AM
> To: Dan Magenheimer
> Cc: Gaurav Kukreja; tmem-devel at oss.oracle.com; rusty at rustcorp.com.au
> Subject: Re: [Tmem-devel] Implementing Transcendent Memory on Lguest
> 
> On 02/08/2010 11:04 PM, Dan Magenheimer wrote:
> >
> > I'm not very familiar with virtio but tmem requires synchronous
> > data transfer between the "tmem server" (hypervisor) and the
> > "tmem client" (guest).  I suspect that virtio assumes an
> > asynchronous model.  If a virtio device can be configured
> > as a synchronous device then your idea might work.
> >
> 
> virtio can be made to work synchronously. For virtio version of
> "preswap", refer this:
> http://oss.oracle.com/pipermail/tmem-devel/2010-January.txt
> 
> It creates "vswap" device which swaps directly over hypervisor.
> Pages are transferred to host using virtio in synchronous manner.
> 
> (Links to code are at the end of above archived mail)
> 
> Nitin
> 
> 
> 
> >
> > =============
> >
> > From: Gaurav Kukreja [mailto:mailme.gaurav at gmail.com]
> > Sent: Sunday, February 07, 2010 11:11 PM
> > To: tmem-devel at oss.oracle.com; rusty at rustcorp.com.au
> > Subject: [Tmem-devel] Implementing Transcendent Memory on Lguest
> >
> > Hi,
> >
> > I have been working on trying to implement Transcendent Memory in
> lguest.
> >
> > So far, Tmem on lguest is just working very rudimentarily. I am
> currently working, on virtio balloon driver for the lguest, trying to
> get it to work.
> >
> > I was wondering, and maybe this is vague, whether is it possible to
> create a implementation of Transcendent Memory, as a Virtio Device. I
> have read Rusty's paper on Virtio. I am yet to find out of the
> technical issues regarding the same.
> >
> > Let us please evaluate, whether, there would be any benefits of
> implementing, Transcendent Memory as a Virtio device. I dont know,
> anything about KVM, but would it then be possible to port Tmem, to KVM
> easily?
> >
> > Regards,
> >
>