[Qemu-devel] Re: [PATCH v5 4/5] Inter-VM shared memory PCI device

[Cam Macdonell]

On Tue, May 11, 2010 at 12:13 PM, Avi Kivity <address@hidden> wrote:
> On 05/11/2010 08:05 PM, Anthony Liguori wrote:
>>
>> On 05/11/2010 11:39 AM, Cam Macdonell wrote:
>>>
>>> Most of the people I hear from who are using my patch are using a peer
>>> model to share data between applications (simulations, JVMs, etc).
>>> But guest-to-host applications work as well of course.
>>>
>>> I think "transparent migration" can be achieved by making the
>>> connected/disconnected state transparent to the application.
>>>
>>> When using the shared memory server, the server has to be setup anyway
>>> on the new host and copying the memory region could be part of that as
>>> well if the application needs the contents preserved.  I don't think
>>> it has to be handled by the savevm/loadvm operations.  There's little
>>> difference between naming one VM the master or letting the shared
>>> memory server act like a master.
>>
>> Except that to make it work with the shared memory server, you need the
>> server to participate in the live migration protocol which is something I'd
>> prefer to avoid at it introduces additional down time.
>
> We can tunnel its migration data through qemu.  Of course, gathering its
> dirty bitmap will be interesting.  DSM may be the way to go here (we can
> even live migrate qemu through DSM: share the guest address space and
> immediately start running on the destination node; the guest will fault its
> memory to the destination.  An advantage is that that the cpu load is
> immediately transferred.
>

Given the potential need to develop DSM and migrating multiple VMs
simultaneously as well as few details to decide on, can the patch
series (with other review tweaks fixed) be accepted without migration
support?  I'll continue to work on it of course, but I think the patch
is useful to users without migration at the moment.

Cam