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Date: Tue, 24 Apr 2018 16:44:17 +0200
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 3/3] pc-dimm: factor out address space
 logic into MemoryDevice code
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To: David Hildenbrand <david@redhat.com>
Cc: Pankaj Gupta <pagupta@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, "Michael S . Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, Marcel Apfelbaum <marcel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, David Gibson <david@gibson.dropbear.id.au>, Richard Henderson <rth@twiddle.net>

On Tue, 24 Apr 2018 15:41:23 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 24.04.2018 15:31, Igor Mammedov wrote:
> > On Mon, 23 Apr 2018 14:52:37 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >   
> >>>     
> >>>> +    /* we will need a new memory slot for kvm and vhost */
> >>>> +    if (kvm_enabled() && !kvm_has_free_slot(machine)) {
> >>>> +        error_setg(errp, "hypervisor has no free memory slots left");
> >>>> +        return;
> >>>> +    }
> >>>> +    if (!vhost_has_free_slot()) {
> >>>> +        error_setg(errp, "a used vhost backend has no free memory slots left");
> >>>> +        return;
> >>>> +    }    
> >>> move these checks to pre_plug time
> >>>     
> >>>> +
> >>>> +    memory_region_add_subregion(&hpms->mr, addr - hpms->base, mr);    
> >>> missing vmstate registration?    
> >>
> >> Missed this one: To be called by the caller. Important because e.g. for
> >> virtio-pmem we don't want this (I assume :) ).  
> > if pmem isn't on shared storage, then We'd probably want to migrate
> > it as well, otherwise target would experience data loss.
> > Anyways, I'd just reat it as normal RAM in migration case  
> 
> Yes, if we realize that all MemoryDevices need this call, we can move it
> to that place, too.
> 
> Wonder if we might want to make this configurable for virtio-pmem later
> on (via a flag or sth like that).
I don't see any reason why we wouldn't like it to be migrated,
it's the same as nvdimm but with another qemu:guest ABI
and async flush instead of sync one we have with nvdimm.