linux-kernel - [PATCH v2 1/3] mm: Replace use of system_unbound_wq with system_dfl

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Message-ID: <20260113114630.152942-2-marco.crivellari@suse.com>
Date: Tue, 13 Jan 2026 12:46:28 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH v2 1/3] mm: Replace use of system_unbound_wq with system_dfl_wq

This patch continues the effort to refactor workqueue APIs, which has begun
with the changes introducing new workqueues and a new alloc_workqueue flag:

   commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
   commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

The point of the refactoring is to eventually alter the default behavior of
workqueues to become unbound by default so that their workload placement is
optimized by the scheduler.

Before that to happen, workqueue users must be converted to the better named
new workqueues with no intended behaviour changes:

   system_wq -> system_percpu_wq
   system_unbound_wq -> system_dfl_wq

This way the old obsolete workqueues (system_wq, system_unbound_wq) can be
removed in the future.

Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 mm/backing-dev.c | 2 +-
 mm/kfence/core.c | 6 +++---
 mm/memcontrol.c  | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c5740c6d37a2..2f65b5416228 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -939,7 +939,7 @@ void wb_memcg_offline(struct mem_cgroup *memcg)
 	memcg_cgwb_list->next = NULL;	/* prevent new wb's */
 	spin_unlock_irq(&cgwb_lock);
 
-	queue_work(system_unbound_wq, &cleanup_offline_cgwbs_work);
+	queue_work(system_dfl_wq, &cleanup_offline_cgwbs_work);
 }
 
 /**
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 577a1699c553..36cc78ede411 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -878,7 +878,7 @@ static void toggle_allocation_gate(struct work_struct *work)
 	/* Disable static key and reset timer. */
 	static_branch_disable(&kfence_allocation_key);
 #endif
-	queue_delayed_work(system_unbound_wq, &kfence_timer,
+	queue_delayed_work(system_dfl_wq, &kfence_timer,
 			   msecs_to_jiffies(kfence_sample_interval));
 }
 
@@ -928,7 +928,7 @@ static void kfence_init_enable(void)
 #endif
 
 	WRITE_ONCE(kfence_enabled, true);
-	queue_delayed_work(system_unbound_wq, &kfence_timer, 0);
+	queue_delayed_work(system_dfl_wq, &kfence_timer, 0);
 
 	pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
 		CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,
@@ -1024,7 +1024,7 @@ static int kfence_enable_late(void)
 		return kfence_init_late();
 
 	WRITE_ONCE(kfence_enabled, true);
-	queue_delayed_work(system_unbound_wq, &kfence_timer, 0);
+	queue_delayed_work(system_dfl_wq, &kfence_timer, 0);
 	pr_info("re-enabled\n");
 	return 0;
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 86f43b7e5f71..6b69b8ee023b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -644,7 +644,7 @@ static void flush_memcg_stats_dwork(struct work_struct *w)
 	 * in latency-sensitive paths is as cheap as possible.
 	 */
 	__mem_cgroup_flush_stats(root_mem_cgroup, true);
-	queue_delayed_work(system_unbound_wq, &stats_flush_dwork, FLUSH_TIME);
+	queue_delayed_work(system_dfl_wq, &stats_flush_dwork, FLUSH_TIME);
 }
 
 unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
@@ -3872,7 +3872,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 		goto offline_kmem;
 
 	if (unlikely(mem_cgroup_is_root(memcg)) && !mem_cgroup_disabled())
-		queue_delayed_work(system_unbound_wq, &stats_flush_dwork,
+		queue_delayed_work(system_dfl_wq, &stats_flush_dwork,
 				   FLUSH_TIME);
 	lru_gen_online_memcg(memcg);
 
-- 
2.52.0