cgroup/cpuset: Further optimize code if CONFIG_CPUSETS_V1 not set

JIRA: https://issues.redhat.com/browse/RHEL-107751
Conflicts:
  A minor context diff in the last cpuset_css_offline() hunk due to
  the presence of a later upstream commit a22b3d5 ("cgroup/cpuset:
  Fix race between newly created partition and dying one").

commit c4c9ceb
Author: Waiman Long <longman@redhat.com>
Date:   Sat, 9 Nov 2024 21:50:23 -0500

    cgroup/cpuset: Further optimize code if CONFIG_CPUSETS_V1 not set

    Currently the cpuset code uses group_subsys_on_dfl() to check if we
    are running with cgroup v2. If CONFIG_CPUSETS_V1 isn't set, there is
    really no need to do this check and we can optimize out some of the
    unneeded v1 specific code paths. Introduce a new cpuset_v2() and use it
    to replace the cgroup_subsys_on_dfl() check to further optimize the
    code.

    Signed-off-by: Waiman Long <longman@redhat.com>
    Signed-off-by: Tejun Heo <tj@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

kernel/cgroup/cpuset.c

@@ -297,6 +297,12 @@ static inline void dec_attach_in_progress(struct cpuset *cs)
 	mutex_unlock(&cpuset_mutex);
 }
 
+static inline bool cpuset_v2(void)
+{
+	return !IS_ENABLED(CONFIG_CPUSETS_V1) ||
+		cgroup_subsys_on_dfl(cpuset_cgrp_subsys);
+}
+
 /*
  * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
  * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
@@ -307,7 +313,7 @@ static inline void dec_attach_in_progress(struct cpuset *cs)
  */
 static inline bool is_in_v2_mode(void)
 {
-	return cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+	return cpuset_v2() ||
 	      (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
 }
 
@@ -742,7 +748,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
 	int nslot;		/* next empty doms[] struct cpumask slot */
 	struct cgroup_subsys_state *pos_css;
 	bool root_load_balance = is_sched_load_balance(&top_cpuset);
-	bool cgrpv2 = cgroup_subsys_on_dfl(cpuset_cgrp_subsys);
+	bool cgrpv2 = cpuset_v2();
 	int nslot_update;
 
 	doms = NULL;
@@ -1215,7 +1221,7 @@ static void reset_partition_data(struct cpuset *cs)
 {
 	struct cpuset *parent = parent_cs(cs);
 
-	if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+	if (!cpuset_v2())
 		return;
 
 	lockdep_assert_held(&callback_lock);
@@ -2097,7 +2103,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		 */
 		if (!cp->partition_root_state && !force &&
 		    cpumask_equal(tmp->new_cpus, cp->effective_cpus) &&
-		    (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+		    (!cpuset_v2() ||
 		    (is_sched_load_balance(parent) == is_sched_load_balance(cp)))) {
 			pos_css = css_rightmost_descendant(pos_css);
 			continue;
@@ -2174,8 +2180,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		 * from parent if current cpuset isn't a valid partition root
 		 * and their load balance states differ.
 		 */
-		if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
-		    !is_partition_valid(cp) &&
+		if (cpuset_v2() && !is_partition_valid(cp) &&
 		    (is_sched_load_balance(parent) != is_sched_load_balance(cp))) {
 			if (is_sched_load_balance(parent))
 				set_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
@@ -2191,8 +2196,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		 */
 		if (!cpumask_empty(cp->cpus_allowed) &&
 		    is_sched_load_balance(cp) &&
-		   (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
-		    is_partition_valid(cp)))
+		   (!cpuset_v2() || is_partition_valid(cp)))
 			need_rebuild_sched_domains = true;
 
 		rcu_read_lock();
@@ -2337,7 +2341,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 
 	retval = validate_change(cs, trialcs);
 
-	if ((retval == -EINVAL) && cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) {
+	if ((retval == -EINVAL) && cpuset_v2()) {
 		struct cgroup_subsys_state *css;
 		struct cpuset *cp;
 
@@ -2824,8 +2828,7 @@ int cpuset_update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
 	spin_unlock_irq(&callback_lock);
 
 	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed) {
-		if (!IS_ENABLED(CONFIG_CPUSETS_V1) ||
-		    cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+		if (cpuset_v2())
 			cpuset_force_rebuild();
 		else
 			rebuild_sched_domains_locked();
@@ -3005,8 +3008,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 		 * migration permission derives from hierarchy ownership in
 		 * cgroup_procs_write_permission()).
 		 */
-		if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
-		    (cpus_updated || mems_updated)) {
+		if (!cpuset_v2() || (cpus_updated || mems_updated)) {
 			ret = security_task_setscheduler(task);
 			if (ret)
 				goto out_unlock;
@@ -3120,8 +3122,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	 * in effective cpus and mems. In that case, we can optimize out
 	 * by skipping the task iteration and update.
 	 */
-	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
-	    !cpus_updated && !mems_updated) {
+	if (cpuset_v2() && !cpus_updated && !mems_updated) {
 		cpuset_attach_nodemask_to = cs->effective_mems;
 		goto out;
 	}
@@ -3471,7 +3472,7 @@ cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
 	INIT_LIST_HEAD(&cs->remote_sibling);
 
 	/* Set CS_MEMORY_MIGRATE for default hierarchy */
-	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+	if (cpuset_v2())
 		__set_bit(CS_MEMORY_MIGRATE, &cs->flags);
 
 	return &cs->css;
@@ -3498,8 +3499,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 	/*
 	 * For v2, clear CS_SCHED_LOAD_BALANCE if parent is isolated
 	 */
-	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
-	    !is_sched_load_balance(parent))
+	if (cpuset_v2() && !is_sched_load_balance(parent))
 		clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
 
 	cpuset_inc();
@@ -3566,8 +3566,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
 	cpus_read_lock();
 	mutex_lock(&cpuset_mutex);
 
-	if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
-	    is_sched_load_balance(cs))
+	if (!cpuset_v2() && is_sched_load_balance(cs))
 		cpuset_update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
 
 	cpuset_dec();