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Subject: Re: [RFC PATCH v2 2/3] device-dax: use fallback nid when numa_node is
 invalid
To:     Jia He <justin.he@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>
Cc:     Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Baoquan He <bhe@redhat.com>,
        Chuhong Yuan <hslester96@gmail.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-nvdimm@lists.01.org,
        Kaly Xin <Kaly.Xin@arm.com>
References: <20200707055917.143653-1-justin.he@arm.com>
 <20200707055917.143653-3-justin.he@arm.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <2409a5d4-e77b-f570-c788-feb4f6ebb498@redhat.com>
Date:   Tue, 7 Jul 2020 13:34:12 +0200
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On 07.07.20 07:59, Jia He wrote:
> Previously, numa_off is set unconditionally at the end of dummy_numa_init(),
> even with a fake numa node. Then ACPI detects node id as NUMA_NO_NODE(-1) in
> acpi_map_pxm_to_node() because it regards numa_off as turning off the numa
> node. Hence dev_dax->target_node is NUMA_NO_NODE on arm64 with fake numa.
> 
> 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 using fallback memory_add_physaddr_to_nid() as nid.
> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
> I noticed that on powerpc memory_add_physaddr_to_nid is not exported for module
> driver. Set it to RFC due to this concern.
> 
>  drivers/dax/kmem.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 275aa5f87399..68e693ca6d59 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -28,20 +28,22 @@ int dev_dax_kmem_probe(struct device *dev)
>  	resource_size_t kmem_end;
>  	struct resource *new_res;
>  	const char *new_res_name;
> -	int numa_node;
> +	int numa_node, new_node;
>  	int rc;
>  
>  	/*
>  	 * Ensure good NUMA information for the persistent memory.
> -	 * Without this check, there is a risk that slow memory
> -	 * could be mixed in a node with faster memory, causing
> -	 * unavoidable performance issues.
> +	 * Without this check, there is a risk but not fatal that slow
> +	 * memory could be mixed in a node with faster memory, causing
> +	 * unavoidable performance issues. Furthermore, fallback node
> +	 * id can be used when numa_node is invalid.
>  	 */
>  	numa_node = dev_dax->target_node;
>  	if (numa_node < 0) {
> -		dev_warn(dev, "rejecting DAX region %pR with invalid node: %d\n",
> -			 res, numa_node);
> -		return -EINVAL;
> +		new_node = memory_add_physaddr_to_nid(kmem_start);
> +		dev_info(dev, "changing nid from %d to %d for DAX region %pR\n",
> +			numa_node, new_node, res);
> +		numa_node = new_node;

Now, the warning does not really make sense. We have NUMA_NO_NODE (< 0),
that is not a change in the nid, but a selection of a nid. Printing
NUMA_NO_NODE does not make too much sense. I suggest just getting rid of
new_node and turning the dev_info() into something like

dev_info(dev, "using nid %d for DAX region with undefined nid %pR\n",
         numa_node, res);


-- 
Thanks,

David / dhildenb