linux-kernel - Re: [patch] x86: set hotpluggable nodes in nodes_possible

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Date:	Wed, 20 Jan 2010 15:32:26 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Haicheng Li <haicheng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch] x86: set hotpluggable nodes in nodes_possible_map

On Wed, 20 Jan 2010, Yinghai Lu wrote:

> > nodes_possible_map does not currently include nodes that have SRAT
> > entries that are all ACPI_SRAT_MEM_HOT_PLUGGABLE since the bit is cleared
> > in nodes_parsed if it does not have an online address range.
> > 
> > Unequivocally setting the bit in nodes_parsed is insufficient since
> > existing code, such as acpi_get_nodes(), assumes all nodes in the map
> > have online address ranges.  In fact, all code using nodes_parsed assumes
> > such nodes represent an address range of online memory.
> > 
> > nodes_possible_map is created by unioning nodes_parsed and
> > cpu_nodes_parsed; the former represents nodes with online memory and the
> > latter represents memoryless nodes.  We now set the bit for hotpluggable
> > nodes in cpu_nodes_parsed so that it also gets set in nodes_possible_map.
> > 
> > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > ---
> >  arch/x86/mm/srat_64.c |    4 +++-
> >  1 files changed, 3 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/mm/srat_64.c b/arch/x86/mm/srat_64.c
> > --- a/arch/x86/mm/srat_64.c
> > +++ b/arch/x86/mm/srat_64.c
> > @@ -229,9 +229,11 @@ update_nodes_add(int node, unsigned long start, unsigned long end)
> >  			printk(KERN_ERR "SRAT: Hotplug zone not continuous. Partly ignored\n");
> >  	}
> >  
> > -	if (changed)
> > +	if (changed) {
> > +		node_set(node, cpu_nodes_parsed);
> >  		printk(KERN_INFO "SRAT: hot plug zone found %Lx - %Lx\n",
> >  				 nd->start, nd->end);
> > +	}
> >  }
> >  
> >  /* Callback for parsing of the Proximity Domain <-> Memory Area mappings */
> 
>         if (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE) {
>                 update_nodes_add(node, start, end);
>                 /* restore nodes[node] */
>                 *nd = oldnode;
>                 if ((nd->start | nd->end) == 0)
>                         node_clear(node, nodes_parsed);
>         }
> 
> removing clearing with nodes_parsed is not working?
> 

As previously discussed in this thread, the semantics of nodes_parsed is 
to define nodes that have online address ranges; all code written to use 
nodes_parsed operates on those address ranges.  Requiring it to also 
support memoryless (or hotpluggable) nodes would require a change in 
semantics in other areas such as acpi_get_nodes() and would be contrary to 
the effort in dc098551 to fix this inconsistency.

I believe Haicheng will be posting an incremental patch that changes the 
name of cpu_nodes_parsed to something such as acpi_nodes_parsed to 
indicate it does not necessarily represent memory but rather another ACPI 
definition: either a node including only cpus or hotpluggable ranges.  
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