Re: [PATCH] Make dynamic/run-time configuration of zonelist order configurable

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Wed, 2007-05-30 at 11:21 +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 29 May 2007 15:48:41 -0400
> Lee Schermerhorn <Lee.Schermerhorn@hp.com> wrote:
> 
> > Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>
> > 
> 
> no problem was found on my ia64 test box.
> 
> But one point..
> 
> > -#ifdef CONFIG_NUMA
> > +#ifdef CONFIG_DYNAMIC_ZONELIST_ORDER
> >  	{
> >  		.ctl_name	= CTL_UNNUMBERED,
> >  		.procname	= "numa_zonelist_order",
> 
> non-NUMA, memory-hotpluggable machine need this control ??
> 

Hi, Kame:

Here was my thinking on that point--actually on the numa_zonelist_order
sysctl in general:

When would it ever be needed?  I think the answer is when the dynamic
configuration didn't "get it right" and you want to fix it w/o reboot.
I agree that it is very likely that you wouldn't want to reboot if
you've gone to all the trouble to support memory hotplug.  In that case,
we have a couple of choices:

1) just enable the config option manually for platforms that support
memory hotplug, or

2) make the option default to 'y' when memory hotplug is configured.

As I tried to indicate in the patch description, because some smallish
systems appear to use NUMA emulation for resource management, they must
enable NUMA support.  However, they may not [I think probably not] need
run-time zoneorder configuration.  I suspect those platforms don't
support memory hotplug at this time either.  Now, the code in question
[sysctl and build_zonelist functions] may be relatively small--i.e.,
less than a page.  But, it all adds up, so I offered a way for small
systems that still wanted NUMA support to get back what we took from
them with the zonelist order patches.

Thoughts?

Lee

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