Re: [PATCH v3 5/6] device-dax: use fallback nid when numa_node is invalid

Dan Williams
2020-07-09T03:38:30Z

On Wed, Jul 8, 2020 at 7:07 PM Jia He <justin.he@arm.com> wrote:
>
> numa_off is set unconditionally at the end of dummy_numa_init(),
> even with a fake numa node. 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 --modeÞvdax --mapÞv -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>
> ---
> drivers/dax/kmem.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 275aa5f87399..218f66057994 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -31,22 +31,23 @@ int dev_dax_kmem_probe(struct device *dev)
> int numa_node;
> int rc;
>
> + /* Hotplug starting at the beginning of the next block: */
> + kmem_start = ALIGN(res->start, memory_block_size_bytes());
> +
> /*
> * 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.
> + * 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;
> + numa_node = memory_add_physaddr_to_nid(kmem_start);

I think this fixup belongs to the core to set a fallback value for
dev_dax->target_node.

I'm close to having patches to provide a functional
phys_addr_to_target_node() for arm64.