Re: [Qemu-devel] [PATCH V13 10/13] NUMA: add qmp command set-mem-policy to set memory policy for NUMA node

[Wanlong Gao <gaowanlong@cn.fujitsu.com>]

On 10/04/2013 04:13 PM, Paolo Bonzini wrote:
> Il 04/10/2013 02:04, Marcelo Tosatti ha scritto:
>>>>>> This QMP command allows user set guest node's memory policy
>>>>>> through the QMP protocol. The qmp-shell command is like:
>>>>>>     set-mem-policy nodeid=0 policy=membind relative=true host-nodes=0-1
>>>>>>
>>>>>> Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
>>>>>> Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
>>>>
>>>> Wanlong Gao,
>>>>
>>>> 1)
>>>>
>>>> Exposing mbind via QMP/HMP on a live guest is interesting because,
>>>> see mbind manpage: 
>>>>
>>>> "By  default,  mbind() only has an effect for new allocations;
>>>> if the pages inside the range have been already touched before
>>>> setting the policy, then the policy has no effect.  This  default
>>>> behavior  may  be  overridden  by  the  MPOL_MF_MOVE  and
>>>> MPOL_MF_MOVE_ALL flags described below."
>>>>
>>>> This means that executing set-mem-policy on a live guest is
>>>> unpredictable: it depends on which pages have been faulted in already.
>>>>
>>>> Should the command be restricted to offline guests?
>> In fact, unless there is a missing point, it should be removed: to solve
>> the device assignment case (memory pinning), mbind must be executed before
>> the memory regions are registered.
>>
> 
> Right.  We can add the command back later as memory-add, together with
> memory hotplug.

OK, will remove the command in this patch set.

Thanks,
Wanlong Gao

> 
> Paolo
>