[PATCH v5 6/9] mm/demotion: Add support for removing node from demotion memory tiers

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

This patch adds the special string "none" as a supported memtier value
that we can use to remove a specific node from being using as demotion target.

For ex:
:/sys/devices/system/node/node1# cat memtier
1
:/sys/devices/system/node/node1# cat ../../memtier/memtier1/nodelist
1-3
:/sys/devices/system/node/node1# echo none > memtier
:/sys/devices/system/node/node1#
:/sys/devices/system/node/node1# cat memtier
:/sys/devices/system/node/node1# cat ../../memtier/memtier1/nodelist
2-3
:/sys/devices/system/node/node1#

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 drivers/base/node.c          |  4 ++++
 include/linux/memory-tiers.h |  1 +
 mm/memory-tiers.c            | 18 +++++++++++++++---
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 599ed64d910f..344786290149 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -582,6 +582,10 @@ static ssize_t memtier_store(struct device *dev,
 	int node = dev->id;
 	int ret;
 
+	if (!strncmp(buf, "none", strlen("none"))) {
+		node_remove_from_memory_tier(node);
+		return count;
+	}
 	ret = kstrtoul(buf, 10, &tier);
 	if (ret)
 		return ret;
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index adc2cb3bf5f8..79bd8d26feb2 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -17,6 +17,7 @@
 
 extern bool numa_demotion_enabled;
 int next_demotion_node(int node);
+void node_remove_from_memory_tier(int node);
 int node_get_memory_tier_id(int node);
 int node_set_memory_tier(int node, int tier);
 int node_reset_memory_tier(int node, int tier);
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 9c82cf4c4bca..b4e72b672d4d 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -253,8 +253,7 @@ static struct memory_tier *__get_memory_tier_from_id(int id)
 	return NULL;
 }
 
-__maybe_unused // temporay to prevent warnings during bisects
-static void node_remove_from_memory_tier(int node)
+void node_remove_from_memory_tier(int node)
 {
 	struct memory_tier *memtier;
 
@@ -320,7 +319,20 @@ int node_reset_memory_tier(int node, int tier)
 	mutex_lock(&memory_tier_lock);
 
 	current_tier = __node_get_memory_tier(node);
-	if (!current_tier || current_tier->dev.id == tier)
+	if (!current_tier) {
+		/*
+		 * If a N_MEMORY node doesn't have a tier index, then
+		 * we removed it from demotion earlier and we are trying
+		 * add it back. Just add the node to requested tier.
+		 */
+		if (node_state(node, N_MEMORY)) {
+			ret = __node_set_memory_tier(node, tier);
+			establish_migration_targets();
+		}
+		goto out;
+	}
+
+	if (current_tier->dev.id == tier)
 		goto out;
 
 	node_clear(node, current_tier->nodelist);
-- 
2.36.1