Re: mm: LTP/memcg testcase regression induced by 8cd7c588decf..66ce520bb7c2 series

[Mel Gorman]

On Tue, Nov 23, 2021 at 12:18:01PM +0100, Mike Galbraith wrote:
> On Tue, 2021-11-23 at 09:13 +0000, Mel Gorman wrote:
> >
> > I'll see can I reproduce this...
> 
> You likely already know this, but just in case, just plunk the below
> into $LTPROOT/runtest/foo, and $LTPROOT/runltp -f foo.
> 
> #DESCRIPTION:Resource Management testing
> memcg_regression        memcg_regression_test.sh
> 

Thanks. Can you try the following patch please?

The test will still take longer to reach OOM and complete as it's stalling
but not as severely.

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 07db03883062..d9166e94eb95 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1057,7 +1057,17 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
 
 		break;
 	case VMSCAN_THROTTLE_NOPROGRESS:
-		timeout = HZ/2;
+		timeout = 1;
+
+		/*
+		 * If kswapd is disabled, reschedule if necessary but do not
+		 * throttle as the system is likely near OOM.
+		 */
+		if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES) {
+			cond_resched();
+			return;
+		}
+
 		break;
 	case VMSCAN_THROTTLE_ISOLATED:
 		timeout = HZ/50;
@@ -3395,7 +3405,7 @@ static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
 		return;
 
 	/* Throttle if making no progress at high prioities. */
-	if (sc->priority < DEF_PRIORITY - 2)
+	if (sc->priority < DEF_PRIORITY - 2 && !sc->nr_reclaimed)
 		reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS);
 }
 
@@ -3415,6 +3425,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 	unsigned long nr_soft_scanned;
 	gfp_t orig_mask;
 	pg_data_t *last_pgdat = NULL;
+	pg_data_t *first_pgdat = NULL;
 
 	/*
 	 * If the number of buffer_heads in the machine exceeds the maximum
@@ -3478,14 +3489,18 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 			/* need some check for avoid more shrink_zone() */
 		}
 
+		if (!first_pgdat)
+			first_pgdat = zone->zone_pgdat;
+
 		/* See comment about same check for global reclaim above */
 		if (zone->zone_pgdat == last_pgdat)
 			continue;
 		last_pgdat = zone->zone_pgdat;
 		shrink_node(zone->zone_pgdat, sc);
-		consider_reclaim_throttle(zone->zone_pgdat, sc);
 	}
 
+	consider_reclaim_throttle(first_pgdat, sc);
+
 	/*
 	 * Restore to original mask to avoid the impact on the caller if we
 	 * promoted it to __GFP_HIGHMEM.