diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 3fdb21a390c1..9273d0969ebd 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -412,13 +412,13 @@ static void throtl_pd_init(struct blkcg_gq *blkg)
 	int rw;
 
 	/*
-	 * If sane_hierarchy is enabled, we switch to properly hierarchical
+	 * If on the default hierarchy, we switch to properly hierarchical
 	 * behavior where limits on a given throtl_grp are applied to the
 	 * whole subtree rather than just the group itself.  e.g. If 16M
 	 * read_bps limit is set on the root group, the whole system can't
 	 * exceed 16M for the device.
 	 *
-	 * If sane_hierarchy is not enabled, the broken flat hierarchy
+	 * If not on the default hierarchy, the broken flat hierarchy
 	 * behavior is retained where all throtl_grps are treated as if
 	 * they're all separate root groups right below throtl_data.
 	 * Limits of a group don't interact with limits of other groups
@@ -426,7 +426,7 @@ static void throtl_pd_init(struct blkcg_gq *blkg)
 	 */
 	parent_sq = &td->service_queue;
 
-	if (cgroup_sane_behavior(blkg->blkcg->css.cgroup) && blkg->parent)
+	if (cgroup_on_dfl(blkg->blkcg->css.cgroup) && blkg->parent)
 		parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
 
 	throtl_service_queue_init(&tg->service_queue, parent_sq);
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c4901c19668b..7bb274487c89 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -256,68 +256,7 @@ struct cgroup {
 
 /* cgroup_root->flags */
 enum {
-	/*
-	 * Unfortunately, cgroup core and various controllers are riddled
-	 * with idiosyncrasies and pointless options.  The following flag,
-	 * when set, will force sane behavior - some options are forced on,
-	 * others are disallowed, and some controllers will change their
-	 * hierarchical or other behaviors.
-	 *
-	 * The set of behaviors affected by this flag are still being
-	 * determined and developed and the mount option for this flag is
-	 * prefixed with __DEVEL__.  The prefix will be dropped once we
-	 * reach the point where all behaviors are compatible with the
-	 * planned unified hierarchy, which will automatically turn on this
-	 * flag.
-	 *
-	 * The followings are the behaviors currently affected this flag.
-	 *
-	 * - Mount options "noprefix", "xattr", "clone_children",
-	 *   "release_agent" and "name" are disallowed.
-	 *
-	 * - When mounting an existing superblock, mount options should
-	 *   match.
-	 *
-	 * - Remount is disallowed.
-	 *
-	 * - rename(2) is disallowed.
-	 *
-	 * - "tasks" is removed.  Everything should be at process
-	 *   granularity.  Use "cgroup.procs" instead.
-	 *
-	 * - "cgroup.procs" is not sorted.  pids will be unique unless they
-	 *   got recycled inbetween reads.
-	 *
-	 * - "release_agent" and "notify_on_release" are removed.
-	 *   Replacement notification mechanism will be implemented.
-	 *
-	 * - "cgroup.clone_children" is removed.
-	 *
-	 * - "cgroup.subtree_populated" is available.  Its value is 0 if
-	 *   the cgroup and its descendants contain no task; otherwise, 1.
-	 *   The file also generates kernfs notification which can be
-	 *   monitored through poll and [di]notify when the value of the
-	 *   file changes.
-	 *
-	 * - If mount is requested with sane_behavior but without any
-	 *   subsystem, the default unified hierarchy is mounted.
-	 *
-	 * - cpuset: tasks will be kept in empty cpusets when hotplug happens
-	 *   and take masks of ancestors with non-empty cpus/mems, instead of
-	 *   being moved to an ancestor.
-	 *
-	 * - cpuset: a task can be moved into an empty cpuset, and again it
-	 *   takes masks of ancestors.
-	 *
-	 * - memcg: use_hierarchy is on by default and the cgroup file for
-	 *   the flag is not created.
-	 *
-	 * - blkcg: blk-throttle becomes properly hierarchical.
-	 *
-	 * - debug: disallowed on the default hierarchy.
-	 */
-	CGRP_ROOT_SANE_BEHAVIOR	= (1 << 0),
-
+	CGRP_ROOT_SANE_BEHAVIOR	= (1 << 0), /* __DEVEL__sane_behavior specified */
 	CGRP_ROOT_NOPREFIX	= (1 << 1), /* mounted subsystems have no named prefix */
 	CGRP_ROOT_XATTR		= (1 << 2), /* supports extended attributes */
 };
@@ -531,20 +470,64 @@ struct cftype {
 extern struct cgroup_root cgrp_dfl_root;
 extern struct css_set init_css_set;
 
+/**
+ * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
+ * @cgrp: the cgroup of interest
+ *
+ * The default hierarchy is the v2 interface of cgroup and this function
+ * can be used to test whether a cgroup is on the default hierarchy for
+ * cases where a subsystem should behave differnetly depending on the
+ * interface version.
+ *
+ * The set of behaviors which change on the default hierarchy are still
+ * being determined and the mount option is prefixed with __DEVEL__.
+ *
+ * List of changed behaviors:
+ *
+ * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
+ *   and "name" are disallowed.
+ *
+ * - When mounting an existing superblock, mount options should match.
+ *
+ * - Remount is disallowed.
+ *
+ * - rename(2) is disallowed.
+ *
+ * - "tasks" is removed.  Everything should be at process granularity.  Use
+ *   "cgroup.procs" instead.
+ *
+ * - "cgroup.procs" is not sorted.  pids will be unique unless they got
+ *   recycled inbetween reads.
+ *
+ * - "release_agent" and "notify_on_release" are removed.  Replacement
+ *   notification mechanism will be implemented.
+ *
+ * - "cgroup.clone_children" is removed.
+ *
+ * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
+ *   and its descendants contain no task; otherwise, 1.  The file also
+ *   generates kernfs notification which can be monitored through poll and
+ *   [di]notify when the value of the file changes.
+ *
+ * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
+ *   take masks of ancestors with non-empty cpus/mems, instead of being
+ *   moved to an ancestor.
+ *
+ * - cpuset: a task can be moved into an empty cpuset, and again it takes
+ *   masks of ancestors.
+ *
+ * - memcg: use_hierarchy is on by default and the cgroup file for the flag
+ *   is not created.
+ *
+ * - blkcg: blk-throttle becomes properly hierarchical.
+ *
+ * - debug: disallowed on the default hierarchy.
+ */
 static inline bool cgroup_on_dfl(const struct cgroup *cgrp)
 {
 	return cgrp->root == &cgrp_dfl_root;
 }
 
-/*
- * See the comment above CGRP_ROOT_SANE_BEHAVIOR for details.  This
- * function can be called as long as @cgrp is accessible.
- */
-static inline bool cgroup_sane_behavior(const struct cgroup *cgrp)
-{
-	return cgrp->root->flags & CGRP_ROOT_SANE_BEHAVIOR;
-}
-
 /* no synchronization, the result can only be used as a hint */
 static inline bool cgroup_has_tasks(struct cgroup *cgrp)
 {
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0ea54af6b133..fb07c6d43aff 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1470,8 +1470,8 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 	struct cgroup_sb_opts opts;
 	unsigned int added_mask, removed_mask;
 
-	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) {
-		pr_err("sane_behavior: remount is not allowed\n");
+	if (root == &cgrp_dfl_root) {
+		pr_err("remount is not allowed\n");
 		return -EINVAL;
 	}
 
@@ -2943,9 +2943,9 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
 
 	/*
 	 * This isn't a proper migration and its usefulness is very
-	 * limited.  Disallow if sane_behavior.
+	 * limited.  Disallow on the default hierarchy.
 	 */
-	if (cgroup_sane_behavior(cgrp))
+	if (cgroup_on_dfl(cgrp))
 		return -EPERM;
 
 	/*
@@ -3031,7 +3031,7 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
 		/* does cft->flags tell us to skip this file on @cgrp? */
 		if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
 			continue;
-		if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
+		if ((cft->flags & CFTYPE_INSANE) && cgroup_on_dfl(cgrp))
 			continue;
 		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
 			continue;
@@ -3764,8 +3764,9 @@ after:
  *
  * All this extra complexity was caused by the original implementation
  * committing to an entirely unnecessary property.  In the long term, we
- * want to do away with it.  Explicitly scramble sort order if
- * sane_behavior so that no such expectation exists in the new interface.
+ * want to do away with it.  Explicitly scramble sort order if on the
+ * default hierarchy so that no such expectation exists in the new
+ * interface.
  *
  * Scrambling is done by swapping every two consecutive bits, which is
  * non-identity one-to-one mapping which disturbs sort order sufficiently.
@@ -3780,7 +3781,7 @@ static pid_t pid_fry(pid_t pid)
 
 static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
 {
-	if (cgroup_sane_behavior(cgrp))
+	if (cgroup_on_dfl(cgrp))
 		return pid_fry(pid);
 	else
 		return pid;
@@ -3883,7 +3884,7 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
 	css_task_iter_end(&it);
 	length = n;
 	/* now sort & (if procs) strip out duplicates */
-	if (cgroup_sane_behavior(cgrp))
+	if (cgroup_on_dfl(cgrp))
 		sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
 	else
 		sort(array, length, sizeof(pid_t), cmppid, NULL);
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index f6b33c696224..f9d4807c869f 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1383,12 +1383,9 @@ static int cpuset_can_attach(struct cgroup_subsys_state *css,
 
 	mutex_lock(&cpuset_mutex);
 
-	/*
-	 * We allow to move tasks into an empty cpuset if sane_behavior
-	 * flag is set.
-	 */
+	/* allow moving tasks into an empty cpuset if on default hierarchy */
 	ret = -ENOSPC;
-	if (!cgroup_sane_behavior(css->cgroup) &&
+	if (!cgroup_on_dfl(css->cgroup) &&
 	    (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
 		goto out_unlock;
 
@@ -2030,7 +2027,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs)
 	static cpumask_t off_cpus;
 	static nodemask_t off_mems;
 	bool is_empty;
-	bool sane = cgroup_sane_behavior(cs->css.cgroup);
+	bool on_dfl = cgroup_on_dfl(cs->css.cgroup);
 
 retry:
 	wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
@@ -2054,12 +2051,12 @@ retry:
 	mutex_unlock(&callback_mutex);
 
 	/*
-	 * If sane_behavior flag is set, we need to update tasks' cpumask
-	 * for empty cpuset to take on ancestor's cpumask. Otherwise, don't
-	 * call update_tasks_cpumask() if the cpuset becomes empty, as
-	 * the tasks in it will be migrated to an ancestor.
+	 * If on_dfl, we need to update tasks' cpumask for empty cpuset to
+	 * take on ancestor's cpumask. Otherwise, don't call
+	 * update_tasks_cpumask() if the cpuset becomes empty, as the tasks
+	 * in it will be migrated to an ancestor.
 	 */
-	if ((sane && cpumask_empty(cs->cpus_allowed)) ||
+	if ((on_dfl && cpumask_empty(cs->cpus_allowed)) ||
 	    (!cpumask_empty(&off_cpus) && !cpumask_empty(cs->cpus_allowed)))
 		update_tasks_cpumask(cs);
 
@@ -2068,12 +2065,12 @@ retry:
 	mutex_unlock(&callback_mutex);
 
 	/*
-	 * If sane_behavior flag is set, we need to update tasks' nodemask
-	 * for empty cpuset to take on ancestor's nodemask. Otherwise, don't
-	 * call update_tasks_nodemask() if the cpuset becomes empty, as
-	 * the tasks in it will be migratd to an ancestor.
+	 * If on_dfl, we need to update tasks' nodemask for empty cpuset to
+	 * take on ancestor's nodemask. Otherwise, don't call
+	 * update_tasks_nodemask() if the cpuset becomes empty, as the
+	 * tasks in it will be migratd to an ancestor.
 	 */
-	if ((sane && nodes_empty(cs->mems_allowed)) ||
+	if ((on_dfl && nodes_empty(cs->mems_allowed)) ||
 	    (!nodes_empty(off_mems) && !nodes_empty(cs->mems_allowed)))
 		update_tasks_nodemask(cs);
 
@@ -2083,13 +2080,13 @@ retry:
 	mutex_unlock(&cpuset_mutex);
 
 	/*
-	 * If sane_behavior flag is set, we'll keep tasks in empty cpusets.
+	 * If on_dfl, we'll keep tasks in empty cpusets.
 	 *
 	 * Otherwise move tasks to the nearest ancestor with execution
 	 * resources.  This is full cgroup operation which will
 	 * also call back into cpuset.  Should be done outside any lock.
 	 */
-	if (!sane && is_empty)
+	if (!on_dfl && is_empty)
 		remove_tasks_in_empty_cpuset(cs);
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index db536e90c8ee..a2a4bd69a7ae 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7024,16 +7024,17 @@ static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
 
 /*
  * Cgroup retains root cgroups across [un]mount cycles making it necessary
- * to verify sane_behavior flag on each mount attempt.
+ * to verify whether we're attached to the default hierarchy on each mount
+ * attempt.
  */
 static void mem_cgroup_bind(struct cgroup_subsys_state *root_css)
 {
 	/*
-	 * use_hierarchy is forced with sane_behavior.  cgroup core
+	 * use_hierarchy is forced on the default hierarchy.  cgroup core
 	 * guarantees that @root doesn't have any children, so turning it
 	 * on for the root memcg is enough.
 	 */
-	if (cgroup_sane_behavior(root_css->cgroup))
+	if (cgroup_on_dfl(root_css->cgroup))
 		mem_cgroup_from_css(root_css)->use_hierarchy = true;
 }