simple_lmk: Reduce unnecessary wake ups

We can check if the waitqueue is actually active before calling wake_up()
in order to avoid an unnecessary wake_up() if the reclaim thread is already
running. Furthermore, the release barrier when zeroing needs_reclaim is
unnecessary, so remove it.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>

drivers/android/simple_lmk.c

@@ -290,7 +290,7 @@ static int simple_lmk_reclaim_thread(void *data)
 	while (1) {
 		wait_event_freezable(oom_waitq, atomic_read(&needs_reclaim));
 		scan_and_kill();
-		atomic_set_release(&needs_reclaim, 0);
+		atomic_set(&needs_reclaim, 0);
 	}
 
 	return 0;
@@ -318,8 +318,12 @@ void simple_lmk_mm_freed(struct mm_struct *mm)
 static int simple_lmk_vmpressure_cb(struct notifier_block *nb,
 				    unsigned long pressure, void *data)
 {
-	if (pressure == 100 && !atomic_cmpxchg_acquire(&needs_reclaim, 0, 1))
-		wake_up(&oom_waitq);
+	if (pressure == 100) {
+		atomic_set(&needs_reclaim, 1);
+		smp_mb__after_atomic();
+		if (waitqueue_active(&oom_waitq))
+			wake_up(&oom_waitq);
+	}
 
 	return NOTIFY_OK;
 }