Re: [PATCH] drivers/base/node.c: export physical address range of given node (Re: NUMA node information for pages)

[Dave Hansen]

On 04/11/2014 04:00 AM, David Rientjes wrote:
> On Thu, 10 Apr 2014, Naoya Horiguchi wrote:
>> > Yes, that's right, but it seems to me that just node_start_pfn and node_end_pfn
>> > is not enough because there can be holes (without any page struct backed) inside
>> > [node_start_pfn, node_end_pfn), and it's not aware of memory hotplug.
>> > 
> So?  Who cares if there are non-addressable holes in part of the span?  
> Ulrich, correct me if I'm wrong, but it seems you're looking for just a 
> address-to-nodeid mapping (or pfn-to-nodeid mapping) and aren't actually 
> expecting that there are no holes in a node for things like acpi or I/O or 
> reserved memory.
...
> I think trying to represent holes and handling different memory models and 
> hotplug in special ways is complete overkill.

This isn't just about memory hotplug or different memory models.  There
are systems out there today, in production, that have layouts like this:

|------Node0-----|
     |------Node1-----|

and this:

|------Node0-----|
     |-Node1-|

For those systems, this interface has no meaning.  Given a page in the
shared-span areas, this interface provides no way to figure out which
node it is in.

If you want a non-portable hack that just works on one system, I'd
suggest parsing the existing firmware tables.
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