Re: [Qemu-devel] [RFC] exec: eliminate ram naming issue as migration

[Tan, Jianfeng]

On 2/7/2018 8:06 PM, Igor Mammedov wrote:
> On Wed, 7 Feb 2018 07:49:58 +0000
> "Tan, Jianfeng" <address@hidden> wrote:
>
> > > -----Original Message-----
> > > From: Paolo Bonzini [mailto:address@hidden
> > > Sent: Tuesday, February 6, 2018 1:32 AM
> > > To: Igor Mammedov
> > > Cc: Tan, Jianfeng; address@hidden; Jason Wang; Maxime Coquelin;
> > > Michael S . Tsirkin
> > > Subject: Re: [Qemu-devel] [RFC] exec: eliminate ram naming issue as
> > > migration
> > >
> > > On 05/02/2018 18:15, Igor Mammedov wrote:
> > > > > > Then we would have both ram block named pc.ram:
> > > > > >                Block Name    PSize
> > > > > >                        pc.ram     4 KiB
> > > > > >        /objects/pc.ram    2 MiB
> > > > > >
> > > > > > But I assume it's a corner case which not really happen.
> > > > > Yeah, you're right. :/  I hadn't thought of hotplug.  It can happen indeed.
> > > > perhaps we should fail object_add memory-backend-foo if it resulted
> > > > in creating ramblock with duplicate id
> > > Note that it would only be duplicated with Jianfeng's patch.  So I'm
> > > worried that his patch is worse than what we have now, because it may
> > > create conflicts with system RAMBlock names are not necessarily
> > > predictable.  Right now, -object creates RAMBlock names that are nicely
> > > constrained within /object/.
> > So we are trading off between the benefit it takes and the bad effect it brings.
> >
> > I'm wondering if the above example is the only failed case this patch leads to, i.e, only there is 
> > a ram named "pc.ram" and "/object/pc.ram" in the src VM?
> >
> > Please also consider the second option, that adding an alias name for RAMBlock; 
> > I'm not a big fan for that one, as it just pushes the problem to 
> > OpenStack/Libvirt.
> looking at provided CLI examples it's configuration issue on src and dst,
> one shall not mix numa and non numa variants.

Aha, that's another thing we also want to change. We now add numa at dst 
node, only because without -numa, we cannot set up the file-baked memory 
with share=on.

For example, "-m xG -mem-path xxx" can set up a file-baked memory, but 
the file is not share-able.

> > Or any other suggestions?
> Fix configuration, namely dst side of it (i.e. use the same -m only variant
> without -numa as it's on src).
>
> BTW, what are you trying to achieve adding -numa on dst?

See above reply.

Thanks,
Jianfeng