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

On 9/15/20 11:59 AM, Daniel P. Berrangé wrote: > On Tue, Sep 15, 2020 at 11:53:56AM +0200, Igor Mammedov wrote: >> On Tue, 15 Sep 2020 10:54:46 +0200 >> Michal Privoznik <mprivozn(a)redhat.com&gt; 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. >> >> you do not need >>   --mem-prealloc >> if you explicitly set "prealloc=yes" on backend. >> >> 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. > > IIRC, we tried todo that in the past and the change to use a backend > impacted migration ABI compatibility. Yes, but the problem there was that the memory IDs were not the same. That is: -m + -mem-path would create a memory-backend-file equivalent and set its ID to pc.ram (assuming this is x86 - hence default-ram-id exposure and tracking). But libvirt did generate different ID back then which was incompatible.