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SubjectRe: [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus
* Michal Hocko <mhocko@kernel.org> [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/20200227182650.GG3771@dhcp22.suse.cz?
>

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: linuxppc-dev@lists.ozlabs.org
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Mel Gorman <mgorman@suse.de>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
> > Cc: Christopher Lameter <cl@linux.com>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> > ---
> > 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

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