On Wed, Jul 31, 2019 at 10:03:09AM +0200, Michal Hocko wrote:

On Wed 31-07-19 09:24:21, Mike Rapoport wrote:

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[ sorry for a late reply too, somehow I missed this thread before ]

On Tue, Jul 30, 2019 at 10:14:15AM +0200, Michal Hocko wrote:

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[Sorry for a late reply]

On Mon 15-07-19 17:55:07, Hoan Tran OS wrote:

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Hi,

On 7/12/19 10:00 PM, Michal Hocko wrote:

[...]

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Hmm, I thought this was selectable. But I am obviously wrong here.
Looking more closely, it seems that this is indeed only about
__early_pfn_to_nid and as such not something that should add a config
symbol. This should have been called out in the changelog though.

Yes, do you have any other comments about my patch?

Not really. Just make sure to explicitly state that
CONFIG_NODES_SPAN_OTHER_NODES is only about __early_pfn_to_nid and that
doesn't really deserve it's own config and can be pulled under NUMA.

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Also while at it, does HAVE_MEMBLOCK_NODE_MAP fall into a similar
bucket? Do we have any NUMA architecture that doesn't enable it?

HAVE_MEMBLOCK_NODE_MAP makes huge difference in node/zone initialization
sequence so it's not only about a singe function.

The question is whether we want to have this a config option or enable
it unconditionally for each NUMA system.

We can make it 'default NUMA', but we can't drop it completely because
microblaze uses sparse_memory_present_with_active_regions() which is
unavailable when HAVE_MEMBLOCK_NODE_MAP=n.

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As I checked with arch Kconfig files, there are 2 architectures, riscv 
and microblaze, do not support NUMA but enable this config.

My take would be that riscv will support NUMA some day.
 

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And 1 architecture, alpha, supports NUMA but does not enable this config.

alpha's NUMA support is BROKEN for more than a decade now, I doubt it'll
ever get fixed.

I can see Al has marked it BROKEN in 2005. Maybe time to rip it out?
Although it doesn't seem to be a lot of code in arch/alpha at first
glance so maybe not worth an effort.
-- 
Michal Hocko
SUSE Labs

-- 
Sincerely yours,
Mike.


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