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From: Uladzislau Rezki <urezki@gmail.com>
Date: Wed, 6 Mar 2024 12:56:28 +0100
To: Z qiang <qiang.zhang1211@gmail.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>, RCU <rcu@vger.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@amd.com>,
	Boqun Feng <boqun.feng@gmail.com>, Hillf Danton <hdanton@sina.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>,
	Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH 2/2] rcu: Allocate WQ with WQ_MEM_RECLAIM bit set
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On Wed, Mar 06, 2024 at 10:15:44AM +0800, Z qiang wrote:
> >
> > 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@gmail.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?
> 
I would like to check perf. figures with it and send out it as a
separate patch if it is worth it.

--
Uladzislau Rezki