Subject: Re: [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus

From: Srikar Dronamraju <[email-masked]>
Date: Thu, 12 Mar 2020 10:57:07 +0530

* Michal Hocko <[email-masked]> [2020-03-11 12:57:35]:

> On Wed 11-03-20 16:32:35, Srikar Dronamraju wrote:
> > A Powerpc system with multiple possible nodes and with CONFIG_NUMA
> > enabled always used to have a node 0, even if node 0 does not any cpus
> > or memory attached to it. As per PAPR, node affinity of a cpu is only
> > available once its present / online. For all cpus that are possible but
> > not present, cpu_to_node() would point to node 0.
> > 
> > To ensure a cpuless, memoryless dummy node is not online, powerpc need
> > to make sure all possible but not present cpu_to_node are set to a
> > proper node.
> 
> Just curious, is this somehow related to
> http://lkml.kernel.org/r/[email-masked]?
> 

The issue I am trying to fix is a known issue in Powerpc since many years.
So this surely not a problem after a75056fc1e7c (mm/memcontrol.c: allocate
shrinker_map on appropriate NUMA node"). 

I tried v5.6-rc4 + a75056fc1e7c but didnt face any issues booting the
kernel. Will work with Sachin/Abdul (reporters of the issue).

> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: Michal Hocko <[email-masked]>
> > Cc: Mel Gorman <[email-masked]>
> > Cc: Vlastimil Babka <[email-masked]>
> > Cc: "Kirill A. Shutemov" <[email-masked]>
> > Cc: Christopher Lameter <[email-masked]>
> > Cc: Michael Ellerman <[email-masked]>
> > Cc: Andrew Morton <[email-masked]>
> > Cc: Linus Torvalds <[email-masked]>
> > Signed-off-by: Srikar Dronamraju <[email-masked]>
> > ---
> >  arch/powerpc/mm/numa.c | 16 ++++++++++++++--
> >  1 file changed, 14 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> > index 8a399db..54dcd49 100644
> > --- a/arch/powerpc/mm/numa.c
> > +++ b/arch/powerpc/mm/numa.c
> > @@ -931,8 +931,20 @@ void __init mem_topology_setup(void)
> >  
> >  	reset_numa_cpu_lookup_table();
> >  
> > -	for_each_present_cpu(cpu)
> > -		numa_setup_cpu(cpu);
> > +	for_each_possible_cpu(cpu) {
> > +		/*
> > +		 * Powerpc with CONFIG_NUMA always used to have a node 0,
> > +		 * even if it was memoryless or cpuless. For all cpus that
> > +		 * are possible but not present, cpu_to_node() would point
> > +		 * to node 0. To remove a cpuless, memoryless dummy node,
> > +		 * powerpc need to make sure all possible but not present
> > +		 * cpu_to_node are set to a proper node.
> > +		 */
> > +		if (cpu_present(cpu))
> > +			numa_setup_cpu(cpu);
> > +		else
> > +			set_cpu_numa_node(cpu, first_online_node);
> > +	}
> >  }
> >  
> >  void __init initmem_init(void)
> > -- 
> > 1.8.3.1
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Thanks and Regards
Srikar Dronamraju