Re: [PATCH - v3?] workqueue: allow rescuer thread to do more work.

[Lai Jiangshan <laijs@cn.fujitsu.com>]

On 12/04/2014 02:02 AM, Tejun Heo wrote:
> So, something like the following.  Only compile tested.  I'll test it
> and post proper patches w/ due credits.
> 
> Thanks.
> 
> Index: work/kernel/workqueue.c
> ===================================================================
> --- work.orig/kernel/workqueue.c
> +++ work/kernel/workqueue.c
> @@ -1804,8 +1804,8 @@ static void pool_mayday_timeout(unsigned
>  	struct worker_pool *pool = (void *)__pool;
>  	struct work_struct *work;
>  
> -	spin_lock_irq(&wq_mayday_lock);		/* for wq->maydays */
> -	spin_lock(&pool->lock);
> +	spin_lock_irq(&pool->lock);
> +	spin_lock(&wq_mayday_lock);		/* for wq->maydays */
>  
>  	if (need_to_create_worker(pool)) {
>  		/*
> @@ -1818,8 +1818,8 @@ static void pool_mayday_timeout(unsigned
>  			send_mayday(work);
>  	}
>  
> -	spin_unlock(&pool->lock);
> -	spin_unlock_irq(&wq_mayday_lock);
> +	spin_unlock(&wq_mayday_lock);
> +	spin_unlock_irq(&pool->lock);
>  
>  	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
>  }
> @@ -2248,12 +2248,29 @@ repeat:
>  		 * Slurp in all works issued via this workqueue and
>  		 * process'em.
>  		 */
> -		WARN_ON_ONCE(!list_empty(&rescuer->scheduled));
> +		WARN_ON_ONCE(!list_empty(scheduled));
>  		list_for_each_entry_safe(work, n, &pool->worklist, entry)
>  			if (get_work_pwq(work) == pwq)
>  				move_linked_works(work, scheduled, &n);
>  
> -		process_scheduled_works(rescuer);
> +		if (!list_empty(scheduled)) {
> +			process_scheduled_works(rescuer);
> +
> +			/*
> +			 * The above execution of rescued work items could
> +			 * have created more to rescue through
> +			 * pwq_activate_first_delayed() or chained
> +			 * queueing.  Let's put @pwq back on mayday list so
> +			 * that such back-to-back work items, which may be
> +			 * being used to relieve memory pressure, don't
> +			 * incur MAYDAY_INTERVAL delay inbetween.
> +			 */
> +			if (need_to_create_worker(pool)) {
> +				spin_lock(&wq_mayday_lock);
> +				list_move_tail(&pwq->mayday_node, &wq->maydays);

how about the pwq is empty now? and ...

> +				spin_unlock(&wq_mayday_lock);
> +			}
> +		}
>  
>  		/*
>  		 * Put the reference grabbed by send_mayday().  @pool won't

and the pwq is scheduled free here> 
>