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Message-ID: <20251020023207.177809-2-longman@redhat.com>
Date: Sun, 19 Oct 2025 22:32:06 -0400
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Michal Koutný <mkoutny@...e.com>
Cc: cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org,
Chen Ridong <chenridong@...wei.com>,
Waiman Long <longman@...hat.com>
Subject: [PATCH 1/2] cgroup/cpuset: Don't track # of local child partitions
The cpuset structure has a nr_subparts field which tracks the number
of child local partitions underneath a particular cpuset. Right now,
nr_subparts is only used in partition_is_populated() to avoid iteration
of child cpusets if the condition is right. So by always performing the
child iteration, we can avoid tracking the number of child partitions
and simplify the code a bit.
Signed-off-by: Waiman Long <longman@...hat.com>
---
kernel/cgroup/cpuset-internal.h | 3 ---
kernel/cgroup/cpuset.c | 41 +++++++++++----------------------
2 files changed, 13 insertions(+), 31 deletions(-)
diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index 337608f408ce..5cac42c5fd97 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -155,9 +155,6 @@ struct cpuset {
/* for custom sched domain */
int relax_domain_level;
- /* number of valid local child partitions */
- int nr_subparts;
-
/* partition root state */
int partition_root_state;
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 52468d2c178a..7aef59ea9627 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -358,8 +358,13 @@ static inline bool is_in_v2_mode(void)
* @excluded_child: a child cpuset to be excluded in task checking
* Return: true if there are tasks, false otherwise
*
- * It is assumed that @cs is a valid partition root. @excluded_child should
- * be non-NULL when this cpuset is going to become a partition itself.
+ * @cs should be a valid partition root or going to become a partition root.
+ * @excluded_child should be non-NULL when this cpuset is going to become a
+ * partition itself.
+ *
+ * Note that a remote partition is not allowed underneath a valid local
+ * or remote partition. So if a non-partition root child is populated,
+ * the whole partition is considered populated.
*/
static inline bool partition_is_populated(struct cpuset *cs,
struct cpuset *excluded_child)
@@ -369,8 +374,6 @@ static inline bool partition_is_populated(struct cpuset *cs,
if (cs->css.cgroup->nr_populated_csets)
return true;
- if (!excluded_child && !cs->nr_subparts)
- return cgroup_is_populated(cs->css.cgroup);
rcu_read_lock();
cpuset_for_each_child(child, css, cs) {
@@ -1302,7 +1305,6 @@ static void reset_partition_data(struct cpuset *cs)
lockdep_assert_held(&callback_lock);
- cs->nr_subparts = 0;
if (cpumask_empty(cs->exclusive_cpus)) {
cpumask_clear(cs->effective_xcpus);
if (is_cpu_exclusive(cs))
@@ -1746,7 +1748,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
int deleting; /* Deleting cpus from parent's effective_cpus */
int old_prs, new_prs;
int part_error = PERR_NONE; /* Partition error? */
- int subparts_delta = 0;
int isolcpus_updated = 0;
struct cpumask *xcpus = user_xcpus(cs);
bool nocpu;
@@ -1771,10 +1772,9 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
if (is_partition_valid(parent))
adding = cpumask_and(tmp->addmask,
xcpus, parent->effective_xcpus);
- if (old_prs > 0) {
+ if (old_prs > 0)
new_prs = -old_prs;
- subparts_delta--;
- }
+
goto write_error;
}
@@ -1829,7 +1829,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
WARN_ON_ONCE(!cpumask_subset(tmp->new_cpus, parent->effective_cpus));
deleting = true;
- subparts_delta++;
} else if (cmd == partcmd_disable) {
/*
* May need to add cpus back to parent's effective_cpus
@@ -1840,7 +1839,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
if (is_partition_valid(cs)) {
cpumask_copy(tmp->addmask, cs->effective_xcpus);
adding = true;
- subparts_delta--;
}
new_prs = PRS_MEMBER;
} else if (newmask) {
@@ -1963,17 +1961,13 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
switch (cs->partition_root_state) {
case PRS_ROOT:
case PRS_ISOLATED:
- if (part_error) {
+ if (part_error)
new_prs = -old_prs;
- subparts_delta--;
- }
break;
case PRS_INVALID_ROOT:
case PRS_INVALID_ISOLATED:
- if (!part_error) {
+ if (!part_error)
new_prs = -old_prs;
- subparts_delta++;
- }
break;
}
}
@@ -2002,11 +1996,9 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
* newly deleted ones will be added back to effective_cpus.
*/
spin_lock_irq(&callback_lock);
- if (old_prs != new_prs) {
+ if (old_prs != new_prs)
cs->partition_root_state = new_prs;
- if (new_prs <= 0)
- cs->nr_subparts = 0;
- }
+
/*
* Adding to parent's effective_cpus means deletion CPUs from cs
* and vice versa.
@@ -2018,10 +2010,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
isolcpus_updated += partition_xcpus_add(new_prs, parent,
tmp->delmask);
- if (is_partition_valid(parent)) {
- parent->nr_subparts += subparts_delta;
- WARN_ON_ONCE(parent->nr_subparts < 0);
- }
spin_unlock_irq(&callback_lock);
update_unbound_workqueue_cpumask(isolcpus_updated);
@@ -2105,8 +2093,6 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
*/
spin_lock_irq(&callback_lock);
make_partition_invalid(child);
- cs->nr_subparts--;
- child->nr_subparts = 0;
spin_unlock_irq(&callback_lock);
notify_partition_change(child, old_prs);
continue;
@@ -4021,7 +4007,6 @@ static void cpuset_handle_hotplug(void)
*/
if (!cpumask_empty(subpartitions_cpus)) {
if (cpumask_subset(&new_cpus, subpartitions_cpus)) {
- top_cpuset.nr_subparts = 0;
cpumask_clear(subpartitions_cpus);
} else {
cpumask_andnot(&new_cpus, &new_cpus,
--
2.51.0
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