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

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 27, 2015 at 09:48:37AM +0100, Igor Mammedov wrote:
> 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.
>

If I allocate two 1G DIMMs, what will be the gap size? 512M? 1G?
It's too much either way.

-- 
MST