linux-kernel - Re: [PATCH 2/2] rcu: Allocate WQ with WQ_MEM

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Date: Wed, 6 Mar 2024 10:15:44 +0800
From: Z qiang <qiang.zhang1211@...il.com>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>, RCU <rcu@...r.kernel.org>, 
	Neeraj upadhyay <Neeraj.Upadhyay@....com>, Boqun Feng <boqun.feng@...il.com>, 
	Hillf Danton <hdanton@...a.com>, Joel Fernandes <joel@...lfernandes.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>, Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH 2/2] rcu: Allocate WQ with WQ_MEM_RECLAIM bit set

>
> synchronize_rcu() users have to be processed regardless
> of memory pressure so our private WQ needs to have at least
> one execution context what WQ_MEM_RECLAIM flag guarantees.
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  kernel/rcu/tree.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 475647620b12..59881a68dd26 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1581,6 +1581,7 @@ static void rcu_sr_put_wait_head(struct llist_node *node)
>  /* Disabled by default. */
>  static int rcu_normal_wake_from_gp;
>  module_param(rcu_normal_wake_from_gp, int, 0644);
> +static struct workqueue_struct *sync_wq;
>
>  static void rcu_sr_normal_complete(struct llist_node *node)
>  {
> @@ -1679,7 +1680,7 @@ static void rcu_sr_normal_gp_cleanup(void)
>          * of outstanding users(if still left) and releasing wait-heads
>          * added by rcu_sr_normal_gp_init() call.
>          */
> -       queue_work(system_highpri_wq, &rcu_state.srs_cleanup_work);
> +       queue_work(sync_wq, &rcu_state.srs_cleanup_work);
>  }
>
>  /*
> @@ -5584,6 +5585,9 @@ void __init rcu_init(void)
>         rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
>         WARN_ON(!rcu_gp_wq);
>
> +       sync_wq = alloc_workqueue("sync_wq", WQ_MEM_RECLAIM, 0);

Why was WQ_HIGHPRI removed?

Thanks
Zqiang


> +       WARN_ON(!sync_wq);
> +
>         /* Fill in default value for rcutree.qovld boot parameter. */
>         /* -After- the rcu_node ->lock fields are initialized! */
>         if (qovld < 0)
> --
> 2.39.2
>
>