Re: [Qemu-devel] [RFC PATCH v3 06/19] Implement "-dimm" command line option

[Avi Kivity]

On 10/19/2012 07:48 PM, Blue Swirl wrote:
>>>
>>> DIMMs would be allowed to be hotplugged in the generic mem-controller 
>>> scheme only
>>> (unless it makes sense to allow hotplug in the remaining pmc DRBs and
>>> start using the generic scheme once we run out of emulated DRBs)
>>>
>>
>> 440fx seems a lost cause, so we can go wild and just implement pv dimms.
> 
> Maybe. But what would be a PV DIMM? Do we need any DIMM-like
> granularity at all, instead the guest could be told to use a list of
> RAM regions with arbitrary start and end addresses? 

Guests are likely to support something that has the same constraints as
real hardware.  If we allow non-power-of-two DIMMs, we might find that
guests don't support them well.

> Isn't ballooning
> also related?

It is related in that it is also a memory hotplug technology.  But
ballooning is subtractive and fine-grained where classic hotplug is
additive and coarse grained.  We can use both together, but I don't
think any work is needed at the qemu level.

> 
>>  For q35 I'd like to stay within the spec.
> 
> That may not last forever when machines have terabytes of memory.

At least there's work for chipset implementers.  Or we can do PV-DIMMs
for q35 too.


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