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

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Message-Id: <20210509165954.347dd3cd8e8815b9dce67cfb@linux-foundation.org>
Date:   Sun, 9 May 2021 16:59:54 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     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 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 ;)