On Tue, Oct 27, 2015 at 10:14:56AM +0100, Igor Mammedov wrote: > On Tue, 27 Oct 2015 10:53:08 +0200 > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > 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" <m...@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. > minimum would be 512, and if backend is 1Gb-hugepage gap will be > backend's natural alignment (i.e. 1Gb).
Is backend configuration even allowed to affect the machine ABI? We need to be able to change backend configuration when migrating the VM to another host. -- Eduardo
