On Fri, Dec 04, 2020 at 13:17:52 +0100, Peter Krempa wrote:
On Thu, Dec 03, 2020 at 13:36:23 +0100, Michal Privoznik wrote:
QEMU gained this new virtio-mem model. It's similar to pc-dimm in a sense that guest uses it as memory, but in a sense very different from it as it can dynamically change allocation, without need for hotplug. More specifically, the device has two attributes more (it has more of course, but these two are important here):
1) block-size - the granularity of the device. You can imagine the device being divided into blocks, each 'block-size' long.
2) requested-size - the portion of the device that is in use by the guest.
And it all works like this: at guest startup/hotplug both block-size and requested-size are specified. When sysadmin wants to give some more memory to the guest, or take some back, they change the 'requested-size' attribute which is propagated to the guest where virtio-mem module takes corresponding action. This means, that 'requested-size' must be a whole number product of 'block-size' and of course has to be in rage [0, max-size] (including). The 'max-size' is yet another attribute but if not set it's "inherited" from corresponding memory-backend-* object.
Therefore, two new elements are introduced under <target/>, to reflect these attributes:
<memory model='virtio'> <target> <size unit='KiB'>4194304</size> <node>0</node> <block unit='KiB'>2048</block> <requested unit='KiB'>524288</requested> </target> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </memory>
The intent here is that <requested/> will be allowed to change via virDomainUpdateDeviceFlags() API.
Note, QEMU does inform us about success of allocation via an event - this is covered in next patches.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- docs/formatdomain.rst | 22 ++++ docs/schemas/domaincommon.rng | 10 ++ src/conf/domain_conf.c | 103 ++++++++++++++++-- src/conf/domain_conf.h | 5 + .../memory-hotplug-virtio-mem.xml | 78 +++++++++++++ ...emory-hotplug-virtio-mem.x86_64-latest.xml | 1 + tests/qemuxml2xmltest.c | 1 + 7 files changed, 213 insertions(+), 7 deletions(-) create mode 100644 tests/qemuxml2argvdata/memory-hotplug-virtio-mem.xml create mode 120000 tests/qemuxml2xmloutdata/memory-hotplug-virtio-mem.x86_64-latest.xml
Disregard any comments about size being actual size ...