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

Jia He
2020-07-07T05:59:44Z

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;
}

/* Hotplug starting at the beginning of the next block: */
@@ -100,6 +102,7 @@ static int dev_dax_kmem_remove(struct device *dev)
resource_size_t kmem_start = res->start;
resource_size_t kmem_size = resource_size(res);
const char *res_name = res->name;
+ int numa_node = dev_dax->target_node;
int rc;

/*
@@ -108,7 +111,10 @@ static int dev_dax_kmem_remove(struct device *dev)
* there is no way to hotremove this memory until reboot because device
* unbind will succeed even if we return failure.
*/
- rc = remove_memory(dev_dax->target_node, kmem_start, kmem_size);
+ if (numa_node < 0)
+ numa_node = memory_add_physaddr_to_nid(kmem_start);
+
+ rc = remove_memory(numa_node, kmem_start, kmem_size);
if (rc) {
any_hotremove_failed = true;
dev_err(dev,
--
2.17.1