linux-kernel - Re: [PATCH v2 2/3] powerpc/numa: Prefer node id queried from vphn

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Date:   Wed, 29 Apr 2020 12:22:29 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Christopher Lameter <cl@...ux.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 2/3] powerpc/numa: Prefer node id queried from vphn

Hello Srikar,

On Tue, Apr 28, 2020 at 03:08:35PM +0530, Srikar Dronamraju wrote:
> Node id queried from the static device tree may not
> be correct. For example: it may always show 0 on a shared processor.
> Hence prefer the node id queried from vphn and fallback on the device tree
> based node id if vphn query fails.
> 
> 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>
> ---
> Changelog v1:->v2:
> - Rebased to v5.7-rc3
> 
>  arch/powerpc/mm/numa.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index b3615b7fdbdf..281531340230 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -719,20 +719,20 @@ static int __init parse_numa_properties(void)
>  	 */
>  	for_each_present_cpu(i) {
>  		struct device_node *cpu;
> -		int nid;
> -
> -		cpu = of_get_cpu_node(i, NULL);
> -		BUG_ON(!cpu);
> -		nid = of_node_to_nid_single(cpu);
> -		of_node_put(cpu);
> +		int nid = vphn_get_nid(i);
> 
>  		/*
>  		 * Don't fall back to default_nid yet -- we will plug
>  		 * cpus into nodes once the memory scan has discovered
>  		 * the topology.
>  		 */
> -		if (nid < 0)
> -			continue;


> +		if (nid == NUMA_NO_NODE) {
> +			cpu = of_get_cpu_node(i, NULL);
> +			if (cpu) {

Why are we not retaining the BUG_ON(!cpu) assert here ?

> +				nid = of_node_to_nid_single(cpu);
> +				of_node_put(cpu);
> +			}
> +		}

Is it possible at this point that both vphn_get_nid(i) and
of_node_to_nid_single(cpu) returns NUMA_NO_NODE ? If so,
should we still call node_set_online() below ?


>  		node_set_online(nid);
>  	}
> 
> -- 
> 2.20.1
> 
--
Thanks and Regards
gautham.