Answer my own question: The corresponding cmd-line parameter for memory hot-add by QEMU monitor is, -object memory-backend-ram,id=mem0,size=1024M -device pc-dimm,id=dimm0,memdev=mem0
2017-01-05 18:12 GMT+08:00 Daniel P. Berrange <berra...@redhat.com>: > On Thu, Jan 05, 2017 at 04:27:26PM +0800, Bob Chen wrote: > > Hi, > > > > According to the docs, the destination Qemu must have the exactly same > > parameters as the source one. So if the source has just finished cpu or > > memory hotplug, what would the dest's parameters be like? > > > > Does DIMM device, or logically QOM object, have to be reflected on the > new > > command-line parameters? > > Yes, if you have hotplugged any type of device since the VM was started, > the QEMU command line args on the target host must include all the original > args from the source QEMU, and also any args reflect to reflect the > hotplugged devices too. > > A further complication is that on the target, you must also make sure you > fully specify *all* device address information (PCI slots, SCSI luns, etc > etc), because the addresses QEMU assigns to a device after hotplug may > not be the same as the addresses QEMU assigns to a device whne coldplug. > > eg if you boot a guest with 1 NIC + 1 disk, and then hotplug a 2nd NIC > you might get > > 1st NIC == PCI slot 2 > 1st disk == PCI slot 3 > 2nd NIC == PCI slot 4 > > if however, you started QEMU with 2 NICs and 1 disk straight away QEMU > might assign addresses in the order > > 1st NIC == PCI slot 2 > 2nd NIC == PCI slot 3 > 1st disk == PCI slot 4 > > this would totally kill a guest OS during live migration as the slots > for devices its using would change. > > So as a general rule when launching QEMU on a target host for migrating, > you must be explicit about all device addresses and not rely on QEMU to > auto-assign addresses. This is quite alot of work to get right, but if > you're using libvirt it'll do pretty much all this automatically for > you. > > Regards, > Daniel > -- > |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ > :| > |: http://libvirt.org -o- http://virt-manager.org > :| > |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ > :| >
