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Message-ID: <20250905085436.95863-2-marco.crivellari@suse.com>
Date: Fri, 5 Sep 2025 10:54:35 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
cgroups@...r.kernel.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>,
Johannes Weiner <hannes@...xchg.org>,
Michal Koutny <mkoutny@...e.com>
Subject: [PATCH 1/2] cgroup: replace use of system_wq with system_percpu_wq
Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.
This lack of consistentcy cannot be addressed without refactoring the API.
system_wq is a per-CPU worqueue, yet nothing in its name tells about that
CPU affinity constraint, which is very often not required by users. Make
it clear by adding a system_percpu_wq.
queue_work() / queue_delayed_work() mod_delayed_work() will now use the
new per-cpu wq: whether the user still stick on the old name a warn will
be printed along a wq redirect to the new one.
This patch add the new system_percpu_wq except for mm, fs and net
subsystem, whom are handled in separated patches.
The old wq will be kept for a few release cylces.
Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
kernel/cgroup/cgroup.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 3caf2cd86e65..1e39355194fd 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -121,7 +121,7 @@ DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem);
/*
* cgroup destruction makes heavy use of work items and there can be a lot
* of concurrent destructions. Use a separate workqueue so that cgroup
- * destruction work items don't end up filling up max_active of system_wq
+ * destruction work items don't end up filling up max_active of system_percpu_wq
* which may lead to deadlock.
*/
static struct workqueue_struct *cgroup_destroy_wq;
--
2.51.0
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