[PATCH REBASE 7/7] qemu: Use memory-backend-* for regular guest memory

[Michal Privoznik]

On 9/15/20 11:53 AM, Igor Mammedov wrote:
> On Tue, 15 Sep 2020 10:54:46 +0200
> Michal Privoznik <mprivozn at redhat.com> wrote:
> 
>> On 9/8/20 3:55 PM, Ján Tomko wrote:
>>> On a Tuesday in 2020, Michal Privoznik wrote:
>>
>>>> diff --git
>>>> a/tests/qemuxml2argvdata/memfd-memory-default-hugepage.x86_64-latest.args
>>>> b/tests/qemuxml2argvdata/memfd-memory-default-hugepage.x86_64-latest.args
>>>> index 5d256c42bc..b43e7d9c3c 100644
>>>> ---
>>>> a/tests/qemuxml2argvdata/memfd-memory-default-hugepage.x86_64-latest.args
>>>> +++
>>>> b/tests/qemuxml2argvdata/memfd-memory-default-hugepage.x86_64-latest.args
>>>> @@ -12,14 +12,16 @@ QEMU_AUDIO_DRV=none \
>>>> -S \
>>>> -object secret,id=masterKey0,format=raw,\
>>>> file=/tmp/lib/domain--1-instance-00000092/master-key.aes \
>>>> --machine pc-i440fx-2.3,accel=kvm,usb=off,dump-guest-core=off \
>>>> +-machine pc-i440fx-2.3,accel=kvm,usb=off,dump-guest-core=off,\
>>>> +memory-backend=pc.ram \
>>>> -cpu qemu64 \
>>>> -m 14336 \
>>>> --mem-prealloc \
>>>> +-object memory-backend-memfd,id=pc.ram,hugetlb=yes,hugetlbsize=2097152,\
>>>> +share=yes,prealloc=yes,size=15032385536 \
>>>> -overcommit mem-lock=off \
>>>> -smp 8,sockets=1,dies=1,cores=8,threads=1 \
>>>> -object
>>>> memory-backend-memfd,id=ram-node0,hugetlb=yes,hugetlbsize=2097152,\
>>>> -share=yes,size=15032385536,host-nodes=3,policy=preferred \
>>>> +share=yes,prealloc=yes,size=15032385536,host-nodes=3,policy=preferred \
>>>> -numa node,nodeid=0,cpus=0-7,memdev=ram-node0 \
>>>> -uuid 126f2720-6f8e-45ab-a886-ec9277079a67 \
>>>> -display none \
>>>
>>> Should we format all the fields twice in these cases?
>>
>> Ah, good question. Honestly, I don't remember, it was slightly longer
>> ago that I've written these patches. Igor, do you perhaps remember
>> whether libvirt needs to specify both: -machine memory-backend=$id and
>> -object memory-backend-*,id=$id?
> 
> the later defines backend and the former uses it,
> short answer is yes.

Ah, good point. That's the thing I didn't remember.

> 
> you do not need
>   --mem-prealloc
> if you explicitly set "prealloc=yes" on backend.

Yes, we are not doing this for quite some time now.

https://gitlab.com/libvirt/libvirt/-/commit/c658764decf357ef2a064f09235fb6b8bd027f8b

> 
> I'd prefer if libvirt stopped using old -mem-prealloc and -mem-path
> in favor of explicit properties on backend, so QEMU could deprecate
> it and drop aliasing code which uses global properties hack.

That is the whole intent of this series. The only problem was that we 
couldn't just switch to memory-backend-* because that was incompatible 
with -mem-path + -m. And the discussion led us to this solution.

Michal