@@ -918,6 +918,16 @@ struct task_struct *wq_worker_sleeping(struct task_struct *task)
* CONTEXT:
* spin_lock_irq(rq->lock)
*
+ * This function is called during schedule() when a kworker is going
+ * to sleep. It's used by psi to identify aggregation workers during
+ * dequeuing, to allow periodic aggregation to shut-off when that
+ * worker is the last task in the system or cgroup to go to sleep.
+ *
+ * As this function doesn't involve any workqueue-related locking, it
+ * only returns stable values when called from inside the scheduler's
+ * queuing and dequeuing paths, when @task, which must be a kworker,
+ * is guaranteed to not be processing any works.
+ *
* Return:
* The last work function %current executed as a worker, NULL if it
* hasn't executed any work yet.
This function can only be called safely from very specific scheduler contexts. Document those. Suggested-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> --- kernel/workqueue.c | 10 ++++++++++ 1 file changed, 10 insertions(+) Andrew suggested including the explanations that came up during the code review in the function doc. As the function has since been merged, sending as follow-up for 5.1. Thanks!