Re: [PATCH/RFC 0/8] numa - Migrate-on-Fault

[Andi Kleen <andi@firstfloor.org>]

[Adding linux-mm where this should have been in the first place]

On Mon, Nov 15, 2010 at 08:13:14AM -0600, Christoph Lameter wrote:
> On Sun, 14 Nov 2010, KOSAKI Motohiro wrote:
> 
> > Nice!
> 
> Lets not get overenthused. There has been no conclusive proof that the
> overhead introduced by automatic migration schemes is consistently less
> than the benefit obtained by moving the data. Quite to the contrary. We
> have over a decades worth of research and attempts on this issue and there
> was no general improvement to be had that way.

I agree it's not a good idea to enable this by default because
the cost of doing it wrong is too severe. But I suspect
it's a good idea to have optionally available for various workloads.

Good candidates so far:

- Virtualization with KVM (I think it's very promising for  that)
Basically this allows to keep guests local on nodes with their
own NUMA policy without having to statically bind them.

- Some HPC workloads. There were various older reports that 
it helped there.

So basically I think automatic migration would be good to have as
another option to enable in numactl.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only.