[PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

[Mike Rapoport]

On Wed, Jul 31, 2019 at 10:03:09AM +0200, Michal Hocko wrote:
> On Wed 31-07-19 09:24:21, Mike Rapoport wrote:
> > [ 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:
> > > [Sorry for a late reply]
> > > 
> > > On Mon 15-07-19 17:55:07, Hoan Tran OS wrote:
> > > > Hi,
> > > > 
> > > > On 7/12/19 10:00 PM, Michal Hocko wrote:
> > > [...]
> > > > > 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.
> > > 
> > > > > 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.

> > > > 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.
> >  
> > > > 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.