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

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Message-Id: <20260113180115.bdb0cce3b99c72e247424095@linux-foundation.org>
Date: Tue, 13 Jan 2026 18:01:15 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, Tejun Heo
 <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, Frederic
 Weisbecker <frederic@...nel.org>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v2 3/3] mm: add WQ_PERCPU to alloc_workqueue users

On Tue, 13 Jan 2026 12:46:30 +0100 Marco Crivellari <marco.crivellari@...e.com> wrote:

> 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.
> 
> --- 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);
>  }
>  

oops.  I did this:

--- a/mm/slub.c~mm-add-wq_percpu-to-alloc_workqueue-users-fix
+++ a/mm/slub.c
@@ -8546,6 +8546,7 @@ void __init kmem_cache_init_late(void)
 	flushwq = alloc_workqueue("slub_flushwq", WQ_MEM_RECLAIM | WQ_PERCPU,
 				  0);
 	WARN_ON(!flushwq);
+#endif
 }
 
 struct kmem_cache *
_