How does the numa flag affect memory allocation?

How does the numa flag affect memory allocation?

[Carb, Brian A]

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Hello,

I'm trying to get a full grasp of what the "numa" flag does in Xen.

It is my understanding that, with numa=on, Xen will try to allocate
memory for a para VM from the same node as the CPUs that the VM's procs
are pinned to. Thus, in a multi-node system, if we specify a pinning to
a specific node's CPUs in a VM's config file, Xen will allocate the VM's
initial memory from that same node at startup. 

My question is: does this location preference happen for all subsequent
memory allocation? In other words, if I boot a VM configured with some
initial memory and pinned to CPUs in node-X, change the pinning of the
VM's procs to CPUs in node-Y, and then use "xm mem-set" to allocate more
memory, does this new memory come from node-Y?

Also, does the numa flag influence things other than memory allocation? 

Thanks.

brian carb
unisys corporation - malvern, pa


 

 

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Re: How does the numa flag affect memory allocation?

[Andre Przywara]

> It is my understanding that, with numa=on, Xen will try to allocate 
> memory for a para VM from the same node as the CPUs that the VM's procs 
> are pinned to.
Thats true for HVM guests, too.
> Thus, in a multi-node system, if we specify a pinning to
> a specific node's CPUs in a VM's config file, Xen 
> will allocate the VM's initial memory from that same node at startup. 
Correct.
> My question is: does this location preference happen for all subsequent 
> memory allocation? In other words, if I boot a VM configured with some 
> initial memory and pinned to CPUs in node-X, change the pinning of the 
> VM's procs to CPUs in node-Y, and then use "xm mem-set" to allocate more 
> memory, does this new memory come from node-Y?
AFAIK ballooing and NUMA are in the moment mutually exclusive.

Currently I am working on NUMA PV guest support (multiple nodes within a
guest). I posted preliminary patches for HVM guests in August.
If you want to help, you are invited ;-)

Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 277-84917
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