Re: [RFC v1 12/14] rcu/kfree: remove useless monitor_todo flag

[Joel Fernandes <joel@joelfernandes.org>]

On Fri, May 13, 2022 at 04:53:05PM +0200, Uladzislau Rezki wrote:
> > monitor_todo is not needed as the work struct already tracks if work is
> > pending. Just use that to know if work is pending using
> > delayed_work_pending() helper.
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > ---
> >  kernel/rcu/tree.c | 22 +++++++---------------
> >  1 file changed, 7 insertions(+), 15 deletions(-)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 3baf29014f86..3828ac3bf1c4 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3155,7 +3155,6 @@ struct kfree_rcu_cpu_work {
> >   * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
> >   * @lock: Synchronize access to this structure
> >   * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
> > - * @monitor_todo: Tracks whether a @monitor_work delayed work is pending
> >   * @initialized: The @rcu_work fields have been initialized
> >   * @count: Number of objects for which GP not started
> >   * @bkvcache:
> > @@ -3180,7 +3179,6 @@ struct kfree_rcu_cpu {
> >  	struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
> >  	raw_spinlock_t lock;
> >  	struct delayed_work monitor_work;
> > -	bool monitor_todo;
> >  	bool initialized;
> >  	int count;
> >  
> > @@ -3416,9 +3414,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
> >  	// of the channels that is still busy we should rearm the
> >  	// work to repeat an attempt. Because previous batches are
> >  	// still in progress.
> > -	if (!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head)
> > -		krcp->monitor_todo = false;
> > -	else
> > +	if (krcp->bkvhead[0] || krcp->bkvhead[1] || krcp->head)
> >  		schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
> >  
> >  	raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > @@ -3607,10 +3603,8 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> >  
> >  	// Set timer to drain after KFREE_DRAIN_JIFFIES.
> >  	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
> > -	    !krcp->monitor_todo) {
> > -		krcp->monitor_todo = true;
> > +	    !delayed_work_pending(&krcp->monitor_work))
> >  		schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
> > -	}
> >  
> >  unlock_return:
> >  	krc_this_cpu_unlock(krcp, flags);
> > @@ -3685,14 +3679,12 @@ void __init kfree_rcu_scheduler_running(void)
> >  		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
> >  
> >  		raw_spin_lock_irqsave(&krcp->lock, flags);
> > -		if ((!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head) ||
> > -				krcp->monitor_todo) {
> > -			raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > -			continue;
> > +		if (krcp->bkvhead[0] || krcp->bkvhead[1] || krcp->head) {
> > +			if (delayed_work_pending(&krcp->monitor_work)) {
> > +				schedule_delayed_work_on(cpu, &krcp->monitor_work,
> > +						KFREE_DRAIN_JIFFIES);
> > +			}
> >  		}
> > -		krcp->monitor_todo = true;
> > -		schedule_delayed_work_on(cpu, &krcp->monitor_work,
> > -					 KFREE_DRAIN_JIFFIES);
> >  		raw_spin_unlock_irqrestore(&krcp->lock, flags);
> >  	}
> >  }
> > -- 
> >
> Looks good to me from the first glance, but let me know to have a look
> at it more closely.

Thanks, I appreciate it.

 - Joel