Re: [Qemu-devel] [PATCH V4 00/10] Add support for binding guest numa nodes to host numa nodes

[Wanlong Gao]

On 07/05/2013 03:49 AM, Paolo Bonzini wrote:
> Il 04/07/2013 11:53, Wanlong Gao ha scritto:
>> As you know, QEMU can't direct it's memory allocation now, this may cause
>> guest cross node access performance regression.
>> And, the worse thing is that if PCI-passthrough is used,
>> direct-attached-device uses DMA transfer between device and qemu process.
>> All pages of the guest will be pinned by get_user_pages().
>>
>> KVM_ASSIGN_PCI_DEVICE ioctl
>>   kvm_vm_ioctl_assign_device()
>>     =>kvm_assign_device()
>>       => kvm_iommu_map_memslots()
>>         => kvm_iommu_map_pages()
>>            => kvm_pin_pages()
>>
>> So, with direct-attached-device, all guest page's page count will be +1 and
>> any page migration will not work. AutoNUMA won't too.
>>
>> So, we should set the guest nodes memory allocation policy before
>> the pages are really mapped.
>>
>> According to this patch set, we are able to set guest nodes memory policy
>> like following:
>>
>>  -numa node,nodeid=0,mem=1024,cpus=0,mem-policy=membind,mem-hostnode=0-1
>>  -numa node,nodeid=1,mem=1024,cpus=1,mem-policy=interleave,mem-hostnode=1
> 
> Did you see my suggestion to use instead something like this:
> 
>     -numa node,nodeid=0,cpus=0 -numa node,nodeid=1,cpus=1 \
>     -numa mem,nodeid=0,size=1G,policy=membind,hostnode=0-1
>     -numa mem,nodeid=1,size=2G,policy=interleave,hostnode=1
> 
> With an eye to when we'll support memory hotplug, I think it is better.
>  It is not hard to implement it using the OptsVisitor; see
> 14aa0c2de045a6c2fcfadf38c04434fd15909455 for an example of a complex
> schema described with OptsVistor.

OK, got it, thank you.

Wanlong Gao

> 
> Paolo
> 
>