linux-kernel - Re: [PATCH v4 4/4] rcu: Support direct wake-up of synchronize

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Date: Mon, 15 Jan 2024 11:57:39 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Z qiang <qiang.zhang1211@...il.com>
Cc: Z qiang <qiang.zhang1211@...il.com>,
	"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 v4 4/4] rcu: Support direct wake-up of synchronize_rcu()
 users

> Hello, Zqiang.
> 
> > >
> > >         // concurrent sr_normal_gp_cleanup work might observe this update.
> > >         smp_store_release(&rcu_state.srs_done_tail, wait_tail);
> > >         ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail);
> > >
> > > -       if (wait_tail)
> > > +       if (wait_tail->next)
> > >                 queue_work(system_highpri_wq, &sr_normal_gp_cleanup);
> > >
> > 
> > I'm testing these patches :) , one question is as follows:
> > Can we use (WQ_MEM_RECLAIM | WQ_HIGHPR)type of workqueue to perform
> > wake-up actions? avoid kworker creation failure under memory pressure, causing
> > the wake-up action to be delayed.
> > 
> I do not have any objections in not doing that, so we can add.
> 
> Thank for testing this!
> 
I forgot to ask, is your testing simulates a low memory condition so
you see the failure you refer to? Or it is just a possible scenario?

Thanks!

--
Uladzislau Rezki