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



On Tue, 15 Sep 2020 10:59:04 +0100
Daniel P. Berrangé <berrange redhat com> 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 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.
> > 
> > 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. 

for new machine types, that shouldn't happen as they use memory-backend
internally (assuming CLI isn't messed up).

old machine types should cope with switch too, the only thing we were not
able to convert "-numa node,mem" => "-numa memdev" due to odd sizes 'mem' allowed,
that's why "-numa node,mem" were preserved for old machine types.


> 
> 
> Regards,
> Daniel



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