linux-kernel - Re: [PATCH v1 4/5] kvfree_rcu: Refactor kfree_rcu

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Date:   Mon, 10 May 2021 12:09:01 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Michal Hocko <mhocko@...e.com>, Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH v1 4/5] kvfree_rcu: Refactor kfree_rcu_monitor() function

On Sun, May 09, 2021 at 04:59:54PM -0700, Andrew Morton wrote:
> On Wed, 28 Apr 2021 15:44:21 +0200 "Uladzislau Rezki (Sony)" <urezki@...il.com> wrote:
> 
> > Rearm the monitor work directly from its own function that
> > is kfree_rcu_monitor(). So this patch puts the invocation
> > timing control in one place.
> >
> > ...
> >
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3415,37 +3415,44 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
> >  	return !repeat;
> >  }
> >  
> > -static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
> > -					  unsigned long flags)
> > +/*
> > + * This function queues a new batch. If success or nothing to
> > + * drain it returns 1. Otherwise 0 is returned indicating that
> > + * a reclaim kthread has not processed a previous batch.
> > + */
> > +static inline int kfree_rcu_drain(struct kfree_rcu_cpu *krcp)
> >  {
> > +	unsigned long flags;
> > +	int ret;
> > +
> > +	raw_spin_lock_irqsave(&krcp->lock, flags);
> > +
> >  	// Attempt to start a new batch.
> > -	if (queue_kfree_rcu_work(krcp)) {
> > +	ret = queue_kfree_rcu_work(krcp);
> 
> This code has changed slightly in mainline.  Can you please redo,
> retest and resend?
> 
> > +	if (ret)
> >  		// Success! Our job is done here.
> >  		krcp->monitor_todo = false;
> > -		raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > -		return;
> > -	}
> 
> It's conventional to retain the braces here, otherwise the code looks
> weird.  Unless you're a python programmer ;)
> 
> 
Hello, Anrew.

This refactoring is not up to date and is obsolete, instead we have done 
bigger rework of kfree_rcu_monitor(). It is located here:

https://kernel.googlesource.com/pub/scm/linux/kernel/git/paulmck/linux-rcu/+/2349a35d39e7af5eef9064cbd0e42309040551da%5E%21/#F0

--
Vlad Rezki