Hi David

-----Original Message-----
From: David Hildenbrand <redacted>
Sent: Tuesday, July 7, 2020 7:34 PM
To: Justin He <redacted>; Catalin Marinas
[off-list ref]; Will Deacon [off-list ref]; Dan Williams
[off-list ref]; Vishal Verma [off-list ref]; Dave
Jiang [off-list ref]
Cc: Michal Hocko <mhocko@suse.com>; Andrew Morton <akpm@linux-
foundation.org>; Mike Rapoport [off-list ref]; Baoquan He
[off-list ref]; Chuhong Yuan [off-list ref]; linux-arm-
kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
mm@kvack.org; linux-nvdimm@lists.01.org; Kaly Xin [off-list ref]
Subject: Re: [RFC PATCH v2 2/3] device-dax: use fallback nid when
numa_node is invalid

On 07.07.20 07:59, Jia He wrote:

quoted

Previously, numa_off is set unconditionally at the end of

dummy_numa_init(),

quoted

even with a fake numa node. Then ACPI detects node id as NUMA_NO_NODE(-1)

in

quoted

acpi_map_pxm_to_node() because it regards numa_off as turning off the

numa

quoted

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

quoted

isn't present:
$ndctl create-namespace -fe namespace0.0 --mode=devdax --map=dev -s 1g -

a 64K

quoted

kmem dax0.0: rejecting DAX region [mem 0x240400000-0x2bfffffff] with

invalid node: -1

quoted

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 <redacted>
Signed-off-by: Jia He <redacted>
---
I noticed that on powerpc memory_add_physaddr_to_nid is not exported for

module

quoted

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",

quoted

-			 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",

quoted

+			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);

Okay, I will update it as your sugguestion. Thanks

--
Cheers,
Justin (Jia He)


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