linux-kernel - [PATCH 14/33] sched/isolation: Flush memcg workqueues on cpuset isolated partition change

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Message-ID: <20251013203146.10162-15-frederic@kernel.org>
Date: Mon, 13 Oct 2025 22:31:27 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Danilo Krummrich <dakr@...nel.org>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Gabriele Monaco <gmonaco@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Johannes Weiner <hannes@...xchg.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Paolo Abeni <pabeni@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Phil Auld <pauld@...hat.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Simon Horman <horms@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Waiman Long <longman@...hat.com>,
	Will Deacon <will@...nel.org>,
	cgroups@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-block@...r.kernel.org,
	linux-mm@...ck.org,
	linux-pci@...r.kernel.org,
	netdev@...r.kernel.org
Subject: [PATCH 14/33] sched/isolation: Flush memcg workqueues on cpuset isolated partition change

The HK_TYPE_DOMAIN housekeeping cpumask is now modifyable at runtime. In
order to synchronize against memcg workqueue to make sure that no
asynchronous draining is still pending or executing on a newly made
isolated CPU, the housekeeping susbsystem must flush the memcg
workqueues.

However the memcg workqueues can't be flushed easily since they are
queued to the main per-CPU workqueue pool.

Solve this with creating a memcg specific pool and provide and use the
appropriate flushing API.

Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 include/linux/memcontrol.h |  4 ++++
 kernel/sched/isolation.c   |  2 ++
 kernel/sched/sched.h       |  1 +
 mm/memcontrol.c            | 12 +++++++++++-
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 873e510d6f8d..001200df63cf 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1074,6 +1074,8 @@ static inline u64 cgroup_id_from_mm(struct mm_struct *mm)
 	return id;
 }
 
+void mem_cgroup_flush_workqueue(void);
+
 extern int mem_cgroup_init(void);
 #else /* CONFIG_MEMCG */
 
@@ -1481,6 +1483,8 @@ static inline u64 cgroup_id_from_mm(struct mm_struct *mm)
 	return 0;
 }
 
+static inline void mem_cgroup_flush_workqueue(void) { }
+
 static inline int mem_cgroup_init(void) { return 0; }
 #endif /* CONFIG_MEMCG */
 
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 95d69c2102f6..9ec365dea921 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -144,6 +144,8 @@ int housekeeping_update(struct cpumask *mask, enum hk_type type)
 
 	synchronize_rcu();
 
+	mem_cgroup_flush_workqueue();
+
 	kfree(old);
 
 	return 0;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 8fac8aa451c6..8bfc0b4b133f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -44,6 +44,7 @@
 #include <linux/lockdep_api.h>
 #include <linux/lockdep.h>
 #include <linux/memblock.h>
+#include <linux/memcontrol.h>
 #include <linux/minmax.h>
 #include <linux/mm.h>
 #include <linux/module.h>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1033e52ab6cf..1aa14e543f35 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -95,6 +95,8 @@ static bool cgroup_memory_nokmem __ro_after_init;
 /* BPF memory accounting disabled? */
 static bool cgroup_memory_nobpf __ro_after_init;
 
+static struct workqueue_struct *memcg_wq __ro_after_init;
+
 static struct kmem_cache *memcg_cachep;
 static struct kmem_cache *memcg_pn_cachep;
 
@@ -1975,7 +1977,7 @@ static void schedule_drain_work(int cpu, struct work_struct *work)
 {
 	guard(rcu)();
 	if (!cpu_is_isolated(cpu))
-		schedule_work_on(cpu, work);
+		queue_work_on(cpu, memcg_wq, work);
 }
 
 /*
@@ -5092,6 +5094,11 @@ void mem_cgroup_sk_uncharge(const struct sock *sk, unsigned int nr_pages)
 	refill_stock(memcg, nr_pages);
 }
 
+void mem_cgroup_flush_workqueue(void)
+{
+	flush_workqueue(memcg_wq);
+}
+
 static int __init cgroup_memory(char *s)
 {
 	char *token;
@@ -5134,6 +5141,9 @@ int __init mem_cgroup_init(void)
 	cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL,
 				  memcg_hotplug_cpu_dead);
 
+	memcg_wq = alloc_workqueue("memcg", 0, 0);
+	WARN_ON(!memcg_wq);
+
 	for_each_possible_cpu(cpu) {
 		INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work,
 			  drain_local_memcg_stock);
-- 
2.51.0