sched/wait: Introduce wakeup boomark in wake_up_page_bit

Now that we have added breaks in the wait queue scan and allow bookmark
on scan position, we put this logic in the wake_up_page_bit function.

We can have very long page wait list in large system where multiple
pages share the same wait list. We break the wake up walk here to allow
other cpus a chance to access the list, and not to disable the interrupts
when traversing the list for too long. This reduces the interrupt and
rescheduling latency, and excessive page wait queue lock hold time.

[ v2: Remove bookmark_wake_function ]

Signed-off-by: Tim Chen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/wait.h

···
 
 void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
+void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
+		unsigned int mode, void *key, wait_queue_entry_t *bookmark);
 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr);
 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr);

kernel/sched/wait.c

···
 }
 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
 
+void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
+		unsigned int mode, void *key, wait_queue_entry_t *bookmark)
+{
+	__wake_up_common(wq_head, mode, 1, 0, key, bookmark);
+}
+EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
+
 /**
  * __wake_up_sync_key - wake up threads blocked on a waitqueue.
  * @wq_head: the waitqueue

mm/filemap.c

···
 	wait_queue_head_t *q = page_waitqueue(page);
 	struct wait_page_key key;
 	unsigned long flags;
+	wait_queue_entry_t bookmark;
 
 	key.page = page;
 	key.bit_nr = bit_nr;
 	key.page_match = 0;
 
+	bookmark.flags = 0;
+	bookmark.private = NULL;
+	bookmark.func = NULL;
+	INIT_LIST_HEAD(&bookmark.entry);
+
 	spin_lock_irqsave(&q->lock, flags);
-	__wake_up_locked_key(q, TASK_NORMAL, &key);
+	__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
+
+	while (bookmark.flags & WQ_FLAG_BOOKMARK) {
+		/*
+		 * Take a breather from holding the lock,
+		 * allow pages that finish wake up asynchronously
+		 * to acquire the lock and remove themselves
+		 * from wait queue
+		 */
+		spin_unlock_irqrestore(&q->lock, flags);
+		cpu_relax();
+		spin_lock_irqsave(&q->lock, flags);
+		__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
+	}
+
 	/*
 	 * It is possible for other pages to have collided on the waitqueue
 	 * hash, so in that case check for a page match. That prevents a long-