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

[Markus Armbruster]

Vladimir Sementsov-Ogievskiy <address@hidden> writes:

> On 04.02.2016 09:20, Markus Armbruster wrote:
>> Vladimir Sementsov-Ogievskiy <address@hidden> writes:
>>
>>> On 03.02.2016 18:42, Markus Armbruster wrote:
>>>> Eric Blake <address@hidden> 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 <address@hidden>
>>>>>> Signed-off-by: Denis V. Lunev <address@hidden>
>>>>>> CC: Stefan Hajnoczi <address@hidden>
>>>>>> CC: Xiao Guangrong <address@hidden>
>>>>>> CC: "Michael S. Tsirkin" <address@hidden>
>>>>>> CC: Igor Mammedov <address@hidden>
>>>>>> CC: Eric Blake <address@hidden>
>>>>>> CC: Markus Armbruster <address@hidden>
>>>>>> ---
>>>>>> @@ -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)

Sounds like your first approach was the right approach.

>>> 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)

Whatever it takes to get this fix past the gaggle of maintainers (I can
relate to that).

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