[PATCH v2 05/13] conf: Introduce virtio-mem <memory/> model

[David Hildenbrand]

On 22.02.21 17:28, Peter Krempa wrote:
> On Mon, Feb 22, 2021 at 16:57:11 +0100, David Hildenbrand wrote:
>> On 22.02.21 16:46, Michal Privoznik wrote:
>>> On 2/18/21 4:00 PM, David Hildenbrand wrote:
>>>> On 18.02.21 14:31, Michal Privoznik wrote:
> 
> [...]
> 
>> In QEMU, we could make "info balloon" etc. also include virtio-mem provided
>> memory.
>>
>> The main reason I did not do so initially is that
>> 1) It's racy when reading/writing the balloon size. The QEMU interface
>>     is broken as we don't get/set the size of the balloon size but
>>     instead the logical VM size. While someone sets the logical VM size
>>     via virtio-balloon, the logical VM size might change due to virtio-
>>     mem guest activity.
>> 2) I don't want people to be tempted to use both at the same
>>     time.
>>
>> Maybe the right think to do is make "info balloon" report the current
>> logical VM size. If there are races, bad luck - better not use both things
>> at the same time.
> 
> We specifically don't call info balloon or any equivalent nowadays if
> qemu supports the balloon event and we should keep it like that at least
> in terms of the active XML.
> 
> The bulk stats functions we have already call the monitor so it's okay
> to do it there.
> 
> Both virtio-mem and balloon do have events so we should be able to
> update any required definition bits without an explicit call to the
> balloon info apart from the stats code and the refresh on reconnect.
> 

Just to clarify, any BALLOON communication with the outer world 
(set/get/balloon_change) are in terms of "logical VM size", not "balloon 
size".

logical_vm_size = vm_size - balloon_size

vm_size does currently not include virtio-mem provided memory.

-- 
Thanks,

David / dhildenb