linux-kernel - [PATCH v2 3/3] mm: add WQ_PERCPU to alloc

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Message-ID: <20260113114630.152942-4-marco.crivellari@suse.com>
Date: Tue, 13 Jan 2026 12:46:30 +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 3/3] mm: add WQ_PERCPU to alloc_workqueue users

This continues the effort to refactor workqueue APIs, which began with
the introduction of new workqueues and a new alloc_workqueue flag in:

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

The refactoring is going to alter the default behavior of
alloc_workqueue() to be unbound by default.

With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
must now use WQ_PERCPU. For more details see the Link tag below.

In order to keep alloc_workqueue() behavior identical, explicitly request
WQ_PERCPU.

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/slub.c        | 4 +++-
 mm/vmstat.c      | 3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 4c6f0b85a24e..861fee5e48b7 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -974,7 +974,7 @@ static int __init cgwb_init(void)
 	 * system_percpu_wq.  Put them in a separate wq and limit concurrency.
 	 * There's no point in executing many of these in parallel.
 	 */
-	cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
+	cgwb_release_wq = alloc_workqueue("cgwb_release", WQ_PERCPU, 1);
 	if (!cgwb_release_wq)
 		return -ENOMEM;
 
diff --git a/mm/slub.c b/mm/slub.c
index 861592ac5425..bbaa247dce2a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -8542,7 +8542,9 @@ void __init kmem_cache_init(void)
 
 void __init kmem_cache_init_late(void)
 {
-	flushwq = alloc_workqueue("slub_flushwq", WQ_MEM_RECLAIM, 0);
+#ifndef CONFIG_SLUB_TINY
+	flushwq = alloc_workqueue("slub_flushwq", WQ_MEM_RECLAIM | WQ_PERCPU,
+				  0);
 	WARN_ON(!flushwq);
 }
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 65de88cdf40e..580b5ad293d6 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -2274,7 +2274,8 @@ void __init init_mm_internals(void)
 {
 	int ret __maybe_unused;
 
-	mm_percpu_wq = alloc_workqueue("mm_percpu_wq", WQ_MEM_RECLAIM, 0);
+	mm_percpu_wq = alloc_workqueue("mm_percpu_wq",
+				       WQ_MEM_RECLAIM | WQ_PERCPU, 0);
 
 #ifdef CONFIG_SMP
 	ret = cpuhp_setup_state_nocalls(CPUHP_MM_VMSTAT_DEAD, "mm/vmstat:dead",
-- 
2.52.0