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

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Date:	Wed, 3 Dec 2014 13:02:41 -0500
From:	Tejun Heo <tj@...nel.org>
To:	NeilBrown <neilb@...e.de>
Cc:	Jan Kara <jack@...e.cz>, Lai Jiangshan <laijs@...fujitsu.com>,
	Dongsu Park <dongsu.park@...fitbricks.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH - v3?] workqueue: allow rescuer thread to do more work.

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

-- 
tejun
--
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