linux-kernel - Re: [PATCH 1/3] arm64/numa: set numa_off to false when numa node is fake

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Message-ID: <5006eb38-a80e-e368-48db-7f497e15c8af@redhat.com>
Date:   Mon, 6 Jul 2020 10:02:44 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Jia He <justin.he@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Baoquan He <bhe@...hat.com>,
        Chuhong Yuan <hslester96@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Kaly Xin <Kaly.Xin@....com>
Subject: Re: [PATCH 1/3] arm64/numa: set numa_off to false when numa node is
 fake

On 06.07.20 03:19, Jia He wrote:
> Previously, numa_off is set to true unconditionally in dummy_numa_init(),
> even if there is a fake numa node.
> 
> But acpi will translate node id to NUMA_NO_NODE(-1) in acpi_map_pxm_to_node()
> because it regards numa_off as turning off the numa node.
> 
> Without this patch, pmem can't be probed as a RAM device on arm64 if SRAT table
> isn't present.
> 
> $ndctl create-namespace -fe namespace0.0 --mode=devdax --map=dev -s 1g -a 64K
> kmem dax0.0: rejecting DAX region [mem 0x240400000-0x2bfffffff] with invalid node: -1
> kmem: probe of dax0.0 failed with error -22
> 
> This fixes it by setting numa_off to false.
> 
> Signed-off-by: Jia He <justin.he@....com>
> ---
>  arch/arm64/mm/numa.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> index aafcee3e3f7e..7689986020d9 100644
> --- a/arch/arm64/mm/numa.c
> +++ b/arch/arm64/mm/numa.c
> @@ -440,7 +440,8 @@ static int __init dummy_numa_init(void)
>  		return ret;
>  	}
>  
> -	numa_off = true;
> +	/* force numa_off to be false since we have a fake numa node here */
> +	numa_off = false;
>  	return 0;
>  }
>  
> 

What would happen if we use something like this in drivers/dax/kmem.c
instead:

numa_node = dev_dax->target_node;
if (numa_node == NUMA_NO_NODE)
	numa_node = memory_add_physaddr_to_nid(kmem_start);

and eventually dropping the pr_warn in
arm64/memory_add_physaddr_to_nid() ? Would that work?

-- 
Thanks,

David / dhildenb