sysfs: add /sys/kernel/mm/numa/demotion_list

Let user override default system demotion path.

Signed-off-by: Yury Norov <yury.norov@gmail.com>

include/linux/migrate.h

@@ -40,6 +40,8 @@ enum migrate_demotion_flag {
 /* In mm/debug.c; also keep sync with include/trace/events/migrate.h */
 extern const char *migrate_reason_names[MR_TYPES];
 
+extern int node_demotion[MAX_NUMNODES];
+
 #ifdef CONFIG_MIGRATION
 
 #ifndef CONFIG_64BIT
@@ -229,6 +231,7 @@ int migrate_vma_setup(struct migrate_vma *args);
 void migrate_vma_pages(struct migrate_vma *migrate);
 void migrate_vma_finalize(struct migrate_vma *migrate);
 int next_demotion_node(int node);
+int set_demotion_target(int node, int target);
 
 #else /* CONFIG_MIGRATION disabled: */
 
@@ -237,6 +240,11 @@ static inline int next_demotion_node(int node)
 	return NUMA_NO_NODE;
 }
 
+static int set_demotion_target(int node, int target)
+{
+	return -ENOSYS;
+}
+
 #endif /* CONFIG_MIGRATION */
 
 #endif /* _LINUX_MIGRATE_H */

mm/mempolicy.c

@@ -3034,8 +3034,60 @@ static struct kobj_attribute numa_demotion_enabled_attr =
 	__ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
 	       numa_demotion_enabled_store);
 
+static ssize_t numa_demotion_list_show(struct kobject *kobj,
+					  struct kobj_attribute *attr, char *buf)
+{
+	int len, n, pos = 0;
+
+	for_each_online_node(n) {
+		len = sysfs_emit_at(buf, pos, "%d %d\n", n, node_demotion[n]);
+		if (len > 0)
+			pos += len;
+	}
+
+	return pos;
+}
+
+static ssize_t numa_demotion_list_store(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   const char *buf, size_t count)
+{
+	nodemask_t nodes;
+	char *nodelist;
+	int from, to, ret;
+
+	nodelist = strnchr(buf, count, '>');
+	if (!nodelist)
+		return -EINVAL;
+
+	*nodelist++ = 0;
+
+	ret = kstrtoint(buf, 0, &to);
+	if (ret)
+		return ret;
+
+	ret = nodelist_parse(nodelist, nodes);
+	if (ret)
+		return ret;
+
+	for_each_node_mask(from, nodes) {
+		ret = set_demotion_target(from, to);
+		if (ret == -EXDEV)
+			pr_warn("Cross-node loop for demotion: %d>%d\n", to, from);
+		else if (ret)
+			return ret;
+	}
+
+	return count;
+}
+
+static struct kobj_attribute numa_demotion_list_attr =
+	__ATTR(demotion_list, 0644, numa_demotion_list_show,
+	       numa_demotion_list_store);
+
 static struct attribute *numa_attrs[] = {
 	&numa_demotion_enabled_attr.attr,
+	&numa_demotion_list_attr.attr,
 	NULL,
 };
 

mm/migrate.c

@@ -1153,7 +1153,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
  * must be held over all reads to ensure that no cycles are
  * observed.
  */
-static int node_demotion[MAX_NUMNODES] __read_mostly =
+int node_demotion[MAX_NUMNODES] __read_mostly =
 	{[0 ...  MAX_NUMNODES - 1] = NUMA_NO_NODE};
 
 /**
@@ -3218,6 +3218,46 @@ static void set_migration_target_nodes(void)
 	put_online_mems();
 }
 
+static void __set_demotion_target(const int node, const int target)
+{
+	get_online_mems();
+	node_demotion[node] = target;
+	synchronize_rcu();
+	put_online_mems();
+}
+
+int set_demotion_target(const int node, const int target)
+{
+	nodemask_t demotion_path;
+	int next, cnt;
+
+	if (target < NUMA_NO_NODE || target >= MAX_NUMNODES)
+		return  -ERANGE;
+
+	if (target != NUMA_NO_NODE && !node_online(target))
+		return -ENXIO;
+
+	/* Ignore offline nodes. */
+	if (!node_online(node))
+		return 0;
+
+	nodes_clear(demotion_path);
+	node_set(node, demotion_path);
+
+	for (next = target, cnt = 0; next != -1 && cnt < MAX_NUMNODES;
+			next = next_demotion_node(next), cnt++) {
+		if (node_test_and_set(next, demotion_path))
+			/* Demotion path has cross-links (loops). */
+			return -EXDEV;
+	}
+
+	/* nodes_demotion[] broken? */
+	WARN_ON(cnt >= MAX_NUMNODES);
+	__set_demotion_target(node, target);
+
+	return 0;
+}
+
 /*
  * React to hotplug events that might affect the migration targets
  * like events that online or offline NUMA nodes.