Re: [Qemu-devel] [PATCH 3/3] balloon: don't use NVDIMM for ballooning

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

On 04.02.2016 09:20, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:
>
>> On 03.02.2016 18:42, Markus Armbruster wrote:
>>> Eric Blake <eblake@redhat.com> writes:
>>>
>>>> On 01/27/2016 11:51 PM, Vladimir Sementsov-Ogievskiy wrote:
>>>>> NVDIMM for now is planned to use as a backing store for DAX filesystem
>>>>> in the guest and thus this memory is excluded from guest memory
>>>>> management and LRUs.
>>>>>
>>>>> In this case libvirt running QEMU along with configured balloon almost
>>>>> immediately inflates balloon and effectively kill the guest as
>>>>> qemu counts nvdimm as part of the ram.
>>>>>
>>>>> Counting dimm devices as part of the ram for ballooning was started from
>>>>> commit 463756d03:
>>>>>    virtio-balloon: Fix balloon not working correctly when hotplug memory
>>>>>
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>>>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>>>>> CC: Stefan Hajnoczi <stefanha@redhat.com>
>>>>> CC: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>>>>> CC: "Michael S. Tsirkin" <mst@redhat.com>
>>>>> CC: Igor Mammedov <imammedo@redhat.com>
>>>>> CC: Eric Blake <eblake@redhat.com>
>>>>> CC: Markus Armbruster <armbru@redhat.com>
>>>>> ---
>>>>> @@ -308,7 +309,9 @@ static ram_addr_t get_current_ram_size(void)
>>>>>            if (value) {
>>>>>                switch (value->type) {
>>>>>                case MEMORY_DEVICE_INFO_KIND_DIMM:
>>>>> -                size += value->u.dimm->size;
>>>>> +                if (strcmp(value->u.dimm->type, TYPE_NVDIMM)) {
>>>> If you fix 2/3 to use a QAPI enum, then this will be an integer compare
>>>> instead of a strcmp().
>>> Another option is to add a flag to the subtypes of TYPE_PC_DIMM, set it
>>> for the subtypes that should be counted here, and accumulate the sizes
>>> of devices where the flag is set.  Requires iterating directly over the
>>> devices here (like qmp_pc_dimm_device_list() does under the hood) rather
>>> than the MemoryDeviceInfoList returned by qmp_pc_dimm_device_list(),
>> It was my first approach but it was rejected)
>>
>> As another option I can make a function iterating over the devices and
>> return list of them, and then use it instead of
>> qmp_pc_dimm_device_list.. Then, I'll have pointers to devices and can
>> use object_dynamic_cast.
> I fail to see how splitting a tree walk doing stuff into a tree walk
> creating a list and a list walk doing stuff makes things better :)

It will allow me not touch qapi)

>
> Anyway, you guys figure it out.  The only part where I get involved is
> QAPI design.



-- 
Best regards,
Vladimir