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SubjectRe: mm: 5.16 regression: reclaim_throttle leads to stall in near-OOM conditions
On Wed, Nov 24, 2021 at 07:54:49PM +0900, Alexey Avramov wrote:
> > it does eventually get killed OOM
>
> However, a full minute freeze can be a great evil in many situations -
> during such a freeze, the system is completely unresponsive.
>
> So my next question is: How reasonable is the value MAX_RECLAIM_RETRIES?
> Is it also get "out of thin air"?
>

The value is out of thin air but adjusting it may reintroduce issues
with kswapd running at 100% CPU.

> And would it make sense to have buttons to adjust the timeouts?

I don't think we should introduce a tunable for something like this,
it'll be impossible to use properly but can you test this?

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 07db03883062..aa72c0f39dcc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1058,6 +1058,14 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
break;
case VMSCAN_THROTTLE_NOPROGRESS:
timeout = HZ/2;
+
+ /*
+ * If kswapd is disabled, use the minimum timeout as the
+ * system may be at or near OOM.
+ */
+ if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
+ timeout = 1;
+
break;
case VMSCAN_THROTTLE_ISOLATED:
timeout = HZ/50;
@@ -3395,7 +3403,7 @@ 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 +3423,7 @@ 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 +3487,18 @@ 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.
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