Re: [PATCH] per-zone kswapd process

["Martin J. Bligh" <mbligh@aracnet.com>]

> Sorry, I don't buy that.
> 
> a) It does not need to be architecture neutral.  
> 
> b) You surely need a way of communicating the discovered topology
>    to userspace anyway.
> 
> c) $EDITOR /etc/numa-layouf.conf
> 
> d) $EDITOR /etc/kswapd.conf

I guess you could do that, but it seems overly complicated to me.
  
>> I think mbligh recently got the long-needed arch code in
>> for cpu to node... But I'm just not able to make the leap of faith that
>> memory detection is something that can ever comfortably be given to
>> userspace.
> 
> A simple syscall which alows you to launch a kswapd instance against
> a group of zones on any group of CPUs provides complete generality 
> and flexibility to userspace.  And it is architecture neutral.
> 
> If it really is incredibly hard to divine the topology from userspace
> then you need to fix that up.  Provide the topology to userspace.
> Which has the added benefit of providing, umm, the topology to userspace ;)

Can we make a simple default of 1 per node, which is what 99% 
of people want, and then make it more complicated later if people 
complain? It's really pretty easy:

for (node = 0; node < numnodes; ++node) {
	kswapd = kick_off_kswapd_for_node(node);
	kswapd->cpus_allowed = node_to_cpus(node);
}

Or whatever the current cpus_allowed method is. All we seem to need
is node_to_cpus ... I can give that to you tommorow with no problem,
it's trivial.

M.