Re: [RFC PATCH v2 2/3] device-dax: use fallback nid when numa_node is invalid

David Hildenbrand
2020-07-07T11:34:28Z

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