[PATCH V3 7/7] workqueue: Process extra works in rescuer when there are no more to rescue

[Lai Jiangshan <jiangshanlai@gmail.com>]

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

Make the rescuer process more work on the last pwq when there are no
more to rescue for the whole workqueue to help the regular workers in
case it is a temporary relief and to reduce relapse.

Also limit the number of extra works.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
 kernel/workqueue.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9bc155545492..86acf2a9cd41 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3473,10 +3473,30 @@ static bool assign_rescuer_work(struct pool_workqueue *pwq, struct worker *rescu
 		list_del_init(&cursor->entry);
 	}
 
-	/* need rescue? */
-	if (!pwq->nr_active || !need_to_create_worker(pool))
+	/* have work items to rescue? */
+	if (!pwq->nr_active)
 		return false;
 
+	/* need rescue? */
+	if (!need_to_create_worker(pool)) {
+		/*
+		 * The pool has idle workers and doesn't need the rescuer, so it
+		 * could simply return false here. However, the memory pressure
+		 * might not be fully relieved, and if the regular workers later
+		 * go to sleep and the pool runs out of idle workers, mayday
+		 * would be triggered again.
+		 *
+		 * Do more work even if it doesn't need rescue, to help the
+		 * regular workers in case it is a temporary relief and to
+		 * reduce relapse.
+		 *
+		 * Unless the limit is reached or there are other PWQs needing
+		 * help.
+		 */
+		if (limited || !list_empty(&pwq->wq->maydays))
+			return false;
+	}
+
 	/* try to assign a work to rescue */
 	list_for_each_entry_safe_from(work, n, &pool->worklist, entry) {
 		if (get_work_pwq(work) != pwq)
-- 
2.19.1.6.gb485710b