Re: [PATCH v3 6/8] admin: Add theory of operation for write recording commands

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 11/17/2023 5:59 PM, Parav Pandit wrote:
> > From: Zhu, Lingshan <lingshan.zhu@intel.com>
> > Sent: Friday, November 17, 2023 3:23 PM
> >
> >
> > On 11/17/2023 5:41 PM, Parav Pandit wrote:
> > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > Sent: Friday, November 17, 2023 3:08 PM
> > > >
> > > > On Fri, Nov 17, 2023 at 09:14:21AM +0000, Parav Pandit wrote:
> > > > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > > > Sent: Friday, November 17, 2023 2:16 PM In any case you can safely
> > > > > > assume that many users will have migration that takes seconds and
> > > > > > minutes.
> > > > > Strange, but ok. I don't see any problem with current method.
> > > > > 8MB is used for very large VM of 1TB takes minutes. Should be fine.
> > > > The problem is simple: vendors selling devices have no idea how large
> > > > the VM will be. So you have to over-provision for the max VM size.
> > > > If there was a way to instead allocate that in host memory, that
> > > > would improve on this.
> > > Not sure what to over provision for max VM size.
> > > Vendor does not know how many vcpus will be needed. It is no different
> > problem.
> > > When the VM migration is started, the individual tracking range is supplied by
> > the hypervisor to device.
> > > Device allocates necessary memory on this instruction.
> > >
> > > When the VM with certain size is provisioned, the member device can be
> > provisioned for the VM size.
> > > And if it cannot be provisioned, possibly this may not the right member device
> > to use at that point in time.
> > I think Michael means the guest memory can be large, and the device may DMA
> > anywhere, so the device should prepare for the worst case, that could be U64
> > size which can be over-provision.
> No. that is not true.
> The hypervisor supplies the range of addresses on which to track the dirty pages.
> So for sure it is not u64.
hypervisor provides GPA to the guest, but the VA can be very high 
address, means can be u64.
>