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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 30 May 2007 11:52:01 -0400
Lee Schermerhorn <Lee.Schermerhorn@hp.com> wrote:

> 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.
> 
Ah....I know your purpose. What I wanted to say is memory hotplug itseld doesn't need
"manual" zonelist ordering reconfiguration....it calls build_all_zonelists() in automatic way.
Then #ifdef around this sysctl should be CONFIG_NUMA && CONFIG_DYNAMIC_ZONELIST_ORDER.

I know your point and benefits of this patch...(we can remove __init functions if we don't
use it and reduce memory usage to some extent.)
To be honest, I myself doesn't like addling new complicated __init thing. 
But I have no concern if maintainers say ok.

Thanks,
-Kame

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