Re: [PATCH] hw/misc: Add a virtual pci device to dynamically attach memory to QEMU

[David Hildenbrand <david@redhat.com>]

On 27.09.21 10:27, Stefan Hajnoczi wrote:
> On Sun, Sep 26, 2021 at 10:16:14AM +0800, David Dai wrote:
>> Add a virtual pci to QEMU, the pci device is used to dynamically attach memory
>> to VM, so driver in guest can apply host memory in fly without virtualization
>> management software's help, such as libvirt/manager. The attached memory is

We do have virtio-mem to dynamically attach memory to a VM. It could be 
extended by a mechanism for the VM to request more/less memory, that's 
already a planned feature. But yeah, virito-mem memory is exposed as 
ordinary system RAM, not only via a BAR to mostly be managed by user 
space completely.

>> isolated from System RAM, it can be used in heterogeneous memory management for
>> virtualization. Multiple VMs dynamically share same computing device memory
>> without memory overcommit.

This sounds a lot like MemExpand/MemLego ... am I right that this is the 
original design? I recall that VMs share a memory region and dynamically 
agree upon which part of the memory region a VM uses. I further recall 
that there were malloc() hooks that would dynamically allocate such 
memory in user space from the shared memory region.

I can see some use cases for it, although the shared memory design isn't 
what you typically want in most VM environments.

-- 
Thanks,

David / dhildenb