[RFC][PATCH v2 07/21] mm: export node type {pmem|dram} under /sys/bus/node

[Fengguang Wu]

From: Fan Du <fan.du@xxxxxxxxx>

User space migration daemon could check
/sys/bus/node/devices/nodeX/type for node type.

Software can interrogate node type for node memory type and distance
to get desirable target node in migration.

grep -r . /sys/devices/system/node/*/type
/sys/devices/system/node/node0/type:dram
/sys/devices/system/node/node1/type:dram
/sys/devices/system/node/node2/type:pmem
/sys/devices/system/node/node3/type:pmem

Along with next patch which export `peer_node`, migration daemon
could easily find the memory type of current node, and the target
node in case of migration.

grep -r . /sys/devices/system/node/*/peer_node
/sys/devices/system/node/node0/peer_node:2
/sys/devices/system/node/node1/peer_node:3
/sys/devices/system/node/node2/peer_node:0
/sys/devices/system/node/node3/peer_node:1

Signed-off-by: Fan Du <fan.du@xxxxxxxxx>
Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
 drivers/base/node.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- linux.orig/drivers/base/node.c	2018-12-23 19:39:04.763414931 +0800
+++ linux/drivers/base/node.c	2018-12-23 19:39:04.763414931 +0800
@@ -233,6 +233,15 @@ static ssize_t node_read_distance(struct
 }
 static DEVICE_ATTR(distance, S_IRUGO, node_read_distance, NULL);
 
+static ssize_t type_show(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
+	int nid = dev->id;
+
+	return sprintf(buf, is_node_pmem(nid) ? "pmem\n" : "dram\n");
+}
+static DEVICE_ATTR(type, S_IRUGO, type_show, NULL);
+
 static struct attribute *node_dev_attrs[] = {
 	&dev_attr_cpumap.attr,
 	&dev_attr_cpulist.attr,
@@ -240,6 +249,7 @@ static struct attribute *node_dev_attrs[
 	&dev_attr_numastat.attr,
 	&dev_attr_distance.attr,
 	&dev_attr_vmstat.attr,
+	&dev_attr_type.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(node_dev);