[PATCH 6/6] mm/migrate: export whether or not node is toptier in sysf

[Davidlohr Bueso <dave@stgolabs.net>]

This allows userspace to know if the node is considered fast
memory (with CPUs attached to it). While this can be already
derived without a new file, this helps further encapsulate the
concept.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
Resending, just noticed this oatch was never posted.

  Documentation/ABI/stable/sysfs-devices-node |  6 ++++++
  drivers/base/node.c                         | 13 +++++++++++++
  2 files changed, 19 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
index f620c6ae013c..1c21c3985535 100644
--- a/Documentation/ABI/stable/sysfs-devices-node
+++ b/Documentation/ABI/stable/sysfs-devices-node
@@ -198,3 +198,9 @@ Date:		April 2022
  Contact:	Davidlohr Bueso <dave@stgolabs.net>
  Description:
		Shows nodes within the next tier of slower memory below this node.
+
+What:		/sys/devices/system/node/nodeX/memory_toptier
+Date:		April 2022
+Contact:	Davidlohr Bueso <dave@stgolabs.net>
+Description:
+		Node is attached to fast memory or not.
diff --git a/drivers/base/node.c b/drivers/base/node.c
index ab4bae777535..b9de5b0360f2 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -598,12 +598,25 @@ static ssize_t node_read_demotion_path(struct device *dev,
  }
  static DEVICE_ATTR(demotion_path, 0444, node_read_demotion_path, NULL);

+static ssize_t node_read_memory_toptier(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	int nid = dev->id;
+	int len = 0;
+
+	len += sysfs_emit_at(buf, len, "%d\n", !!node_is_toptier(nid));
+
+	return len;
+}
+static DEVICE_ATTR(memory_toptier, 0444, node_read_memory_toptier, NULL);
+
  static struct attribute *node_dev_attrs[] = {
	&dev_attr_meminfo.attr,
	&dev_attr_numastat.attr,
	&dev_attr_distance.attr,
	&dev_attr_vmstat.attr,
	&dev_attr_demotion_path.attr,
+	&dev_attr_memory_toptier.attr,
	NULL
  };

--
2.26.2