Re: [Xen-devel] [PATCH 2/2] Xen ACPI memory hotplug

[Erlon Cruz <sombrafam@xxxxxxxxx>]

On Mon, Mar 11, 2013 at 5:14 AM, Liu, Jinsong <jinsong.liu@xxxxxxxxx> wrote:

Erlon Cruz wrote:
> [snip]
>> +config XEN_ACPI_HOTPLUG_MEMORY
>> +    tristate "Xen ACPI memory hotplug"
>> +    depends on XEN_DOM0 && XEN_STUB && ACPI
>> +    default n
>> +    help
>> +      This is Xen ACPI memory hotplug.
>> +
>> +      Currently Xen only support ACPI memory hot-add. If you want
>> +      to hot-add memory at runtime (the hot-added memory cannot be
>> +      removed until machine stop), select Y/M here, otherwise select N.
>
> I'm wondering if the memory removal is not implemented because of the
> same complication QEMU developers are having. To find a way to keep
> track of the references to to memory to be removed (e.g in DMA block
> operations). Did you had this issue?
>

Sorry for late reply.

Hi Liu, thanks for replying, no problem.

Per my understanding, currently to hot-remove memory is more complicated than to hot-add memory, not only bz of complication of QEMU, but hard to reclaim data structure os/vmm already alloc and occupy. Maybe it would become simpler w/ some h/w assist tech next generation.

Hmm, it makes sense. I read a few discussions about the issue on QEMU list but didn't see any clear solution for the problem.

 

Thanks,
Jinsong

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