linux-kernel - Re: [PATCH 1/3] powerpc/numa: Set numa

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Message-ID: <20200311115735.GM23944@dhcp22.suse.cz>
Date:   Wed, 11 Mar 2020 12:57:35 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Christopher Lameter <cl@...ux.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus

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?

> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: "Kirill A. Shutemov" <kirill@...temov.name>
> Cc: Christopher Lameter <cl@...ux.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.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