[libvirt] [PATCH v2 0/2] qemu: Honor memory mode='strict'

[Michal Privoznik]

On 4/11/19 7:29 PM, Daniel Henrique Barboza wrote:
> 
> 
> On 4/11/19 11:56 AM, Michal Privoznik wrote:
>> On 4/11/19 4:23 PM, Daniel Henrique Barboza wrote:
>>> Hi,
>>>
>>> I've tested these patches again, twice, in similar setups like I tested
>>> the first version (first in a Power8, then in a Power9 server).
>>>
>>> Same results, though. Libvirt will not avoid the launch of a pseries 
>>> guest,
>>> with numanode=strict, even if the numa node does not have available
>>> RAM. If I stress test the memory of the guest to force the allocation,
>>> QEMU exits with an error as soon as the memory of the host numa node
>>> is exhausted.
>>
>> Yes, this is expected. I mean, by default qemu doesn't allocate memory 
>> for the guest fully. You'd have to force it:
>>
>> <memoryBacking>
>>   <allocation mode='immediate'/>
>> </memoryBacking>
>>
> 
> Tried with this extra setting, still no good. Domain still boots, even if
> there is not enough memory to load up all its ram in the NUMA node
> I am setting. For reference, this is the top of the guest XML:
> 
> 
>    <name>vm1</name>
>    <uuid>f48e9e35-8406-4784-875f-5185cb4d47d7</uuid>
>    <memory unit='KiB'>314572800</memory>
>    <currentMemory unit='KiB'>314572800</currentMemory>
>    <memoryBacking>
>      <allocation mode='immediate'/>
>    </memoryBacking>
>    <vcpu placement='static'>16</vcpu>
>    <numatune>
>      <memory mode='strict' nodeset='0'/>
>    </numatune>
>    <os>
>      <type arch='ppc64' machine='pseries'>hvm</type>
>      <boot dev='hd'/>
>    </os>
>    <clock offset='utc'/>
> 
> While doing this test, I recalled that some of my IBM peers recently
> mentioned that they were unable to do a pre-allocation of the RAM
> of a pseries guest using Libvirt, but they were able to do it using QEMU
> directly (using -realtime mlock=on). In fact, I just tried it out with 
> command
> line QEMU and the guest allocated all the memory at boot.

Ah, so looks like -mem-prealloc doesn't work at Power? Can you please check:

1) that -mem-prealloc is on the qemu command line
2) how much memory qemu allocates right after it started the guest? I 
mean, before you start some mem stress test which causes it to allocate 
the memory fully.

> 
> This means that the pseries guest is able to do mem pre-alloc. I'd say that
> there might be something missing somewhere (XML, host setup, libvirt
> config ...) or perhaps even a bug that is preventing Libvirt from doing
> this pre-alloc. This explains why I can't verify this patch series. I'll 
> see if
> I dig it further to understand why when I have the time.

Yeah, I don't know Power well enough to help you. Sorry.

Michal