confuse about kvm memslot size

confuse about kvm memslot size

[cgl14]

hi,
i am a student in Tsinghua Univetsity, i am observing that while manage gpa memory, kvm uses one 512 size memslots array, i was confused about the size 512, will there happens senario that the size grows more than 512? could you please tell me the design principle? 
That will be so kind of your responding.
THANKS.

Guolong Chen,  China.

Re: confuse about kvm memslot size

[David Hildenbrand]

On 13.12.2017 09:25, cgl14@tsinghua.org.cn wrote:
> hi,
> i am a student in Tsinghua Univetsity, i am observing that while manage gpa memory, kvm uses one 512 size memslots array, i was confused about the size 512, will there happens senario that the size grows more than 512? could you please tell me the design principle? 
> That will be so kind of your responding.
> THANKS.
user memory slots are managed and setup by QEMU.
private memory slots are managed and setup by KVM.

We allow 509 out of 512 to be user memory slots. This number turned out
to be sufficient for now.

As one memory slot is usually used for one consecutive memory area in
the guest, only e.g. trying to hotplug a huge number of ACPI Dimms to a
guest would make this number explode. But if I am not wrong, even the
number of ACPI Dimms is limited to 256.

So right now, having more than 512 slots would just be a waste of space
in the KVM module.

> 
> Guolong Chen,  China.
> 


-- 

Thanks,

David / dhildenb

Re: confuse about kvm memslot size

[Quan Xu]

On 2017/12/13 18:11, David Hildenbrand wrote:
> On 13.12.2017 09:25, cgl14@tsinghua.org.cn wrote:
>> hi,
>> i am a student in Tsinghua Univetsity, i am observing that while manage gpa memory, kvm uses one 512 size memslots array, i was confused about the size 512, will there happens senario that the size grows more than 512? could you please tell me the design principle?
>> That will be so kind of your responding.
>> THANKS.
> user memory slots are managed and setup by QEMU.
> private memory slots are managed and setup by KVM.
>
> We allow 509 out of 512 to be user memory slots. This number turned out
> to be sufficient for now.
>
> As one memory slot is usually used for one consecutive memory area in
> the guest, only e.g. trying to hotplug a huge number of ACPI Dimms to a
> guest would make this number explode. But if I am not wrong, even the
> number of ACPI Dimms is limited to 256.
>
> So right now, having more than 512 slots would just be a waste of space
> in the KVM module.
   furthermore, you can read QEMU code, .e.g. pc_memory_init() / 
i440fx_init()..
then you'd be clear the purpose of these  memslots.

Quan
>> Guolong Chen,  China.
>>
>