Re: [PATCH v1 4/5] kvfree_rcu: Refactor kfree_rcu_monitor() function

[Uladzislau Rezki]

Hello, Paul.

> 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.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
>  kernel/rcu/tree.c | 35 +++++++++++++++++++++--------------
>  1 file changed, 21 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index e44d6f8c56f0..229e909ad437 100644
> --- 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);
> +	if (ret)
>  		// Success! Our job is done here.
>  		krcp->monitor_todo = false;
> -		raw_spin_unlock_irqrestore(&krcp->lock, flags);
> -		return;
> -	}
>  
>  	// Previous RCU batch still in progress, try again later.
> -	schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
>  	raw_spin_unlock_irqrestore(&krcp->lock, flags);
> +	return ret;
>  }
>  
>  /*
>   * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
> - * It invokes kfree_rcu_drain_unlock() to attempt to start another batch.
> + * It invokes kfree_rcu_drain() to attempt to start another batch.
>   */
>  static void kfree_rcu_monitor(struct work_struct *work)
>  {
> -	unsigned long flags;
>  	struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu,
>  						 monitor_work.work);
>  
> -	raw_spin_lock_irqsave(&krcp->lock, flags);
> -	if (krcp->monitor_todo)
> -		kfree_rcu_drain_unlock(krcp, flags);
> -	else
> -		raw_spin_unlock_irqrestore(&krcp->lock, flags);
> +	if (kfree_rcu_drain(krcp))
> +		return;
> +
> +	// Not success. A previous batch is still in progress.
> +	// Rearm a work to repeat an attempt of starting another batch.
> +	schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
>  }
>  
>  static enum hrtimer_restart
> -- 
> 2.20.1
> 

Please see below a v2 of this patch. The main difference between v1
is that, the monitor work now is open-coded, thus some extra inline
functions were eliminated: