Re: [Qemu-devel] [PATCH v2] pc: memhp: enforce minimal 128Mb alignment for pc-dimm

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 27 Oct 2015 10:31:21 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Oct 26, 2015 at 02:24:32PM +0100, Igor Mammedov wrote:
> > Yep it's workaround but it works around QEMU's broken virtio
> > implementation in a simple way without need for guest side changes.
> > 
> > Without foreseeable virtio fix it makes memory hotplug unusable and even
> > more so if there were a virtio fix it won't fix old guests since you've
> > said that virtio fix would require changes of both QEMU and guest sides.
> 
> What makes it not foreseeable?
> Apparently only the fact that we have a work-around in place so no one
> works on it.  I can code it up pretty quickly, but I'm flat out of time
> for testing as I'm going on vacation soon, and hard freeze is pretty
> close.
I can lend a hand for testing part.

> 
> GPA space is kind of cheap, but wasting it in chunks of 512M
> seems way too aggressive.
hotplug region is sized with 1Gb alignment reserve per DIMM so we aren't
actually wasting anything here.