kswapd: replace try_to_freeze() with kthread_freezable_should_stop()

Instead of using try_to_freeze, use kthread_freezable_should_stop in
kswapd. By this, we can avoid unnecessary freezing when kswapd should
stop.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Levi Yun <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/vmscan.c

···
 		bool raise_priority = true;
 		bool balanced;
 		bool ret;
+		bool was_frozen;
 
 		sc.reclaim_idx = highest_zoneidx;
 
···
 
 		/* Check if kswapd should be suspending */
 		__fs_reclaim_release(_THIS_IP_);
-		ret = try_to_freeze();
+		ret = kthread_freezable_should_stop(&was_frozen);
 		__fs_reclaim_acquire(_THIS_IP_);
-		if (ret || kthread_should_stop())
+		if (was_frozen || ret)
 			break;
 
 		/*
···
 	WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
 	atomic_set(&pgdat->nr_writeback_throttled, 0);
 	for ( ; ; ) {
-		bool ret;
+		bool was_frozen;
 
 		alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
 		highest_zoneidx = kswapd_highest_zoneidx(pgdat,
···
 		WRITE_ONCE(pgdat->kswapd_order, 0);
 		WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
 
-		ret = try_to_freeze();
-		if (kthread_should_stop())
+		if (kthread_freezable_should_stop(&was_frozen))
 			break;
 
 		/*
 		 * We can speed up thawing tasks if we don't call balance_pgdat
 		 * after returning from the refrigerator
 		 */
-		if (ret)
+		if (was_frozen)
 			continue;
 
 		/*