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Date: Thu, 9 Dec 2021 16:25:54 +0000
From: Mel Gorman <mgorman@...hsingularity.net>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: syzbot <syzbot+dcea9eda277e1090b35f@...kaller.appspotmail.com>,
akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] INFO: task can't die in reclaim_throttle
On Thu, Dec 09, 2021 at 03:51:00PM +0100, Vlastimil Babka wrote:
> On 12/9/21 01:52, syzbot wrote:
> > Hello,
>
> + CC Mel
>
Should be fixed shortly in mmotm. Full diff as it stands is
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 58e744b78c2c..936dc0b6c226 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -277,6 +277,7 @@ enum vmscan_throttle_state {
VMSCAN_THROTTLE_WRITEBACK,
VMSCAN_THROTTLE_ISOLATED,
VMSCAN_THROTTLE_NOPROGRESS,
+ VMSCAN_THROTTLE_CONGESTED,
NR_VMSCAN_THROTTLE,
};
diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index f25a6149d3ba..ca2e9009a651 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -30,12 +30,14 @@
#define _VMSCAN_THROTTLE_WRITEBACK (1 << VMSCAN_THROTTLE_WRITEBACK)
#define _VMSCAN_THROTTLE_ISOLATED (1 << VMSCAN_THROTTLE_ISOLATED)
#define _VMSCAN_THROTTLE_NOPROGRESS (1 << VMSCAN_THROTTLE_NOPROGRESS)
+#define _VMSCAN_THROTTLE_CONGESTED (1 << VMSCAN_THROTTLE_CONGESTED)
#define show_throttle_flags(flags) \
(flags) ? __print_flags(flags, "|", \
{_VMSCAN_THROTTLE_WRITEBACK, "VMSCAN_THROTTLE_WRITEBACK"}, \
{_VMSCAN_THROTTLE_ISOLATED, "VMSCAN_THROTTLE_ISOLATED"}, \
- {_VMSCAN_THROTTLE_NOPROGRESS, "VMSCAN_THROTTLE_NOPROGRESS"} \
+ {_VMSCAN_THROTTLE_NOPROGRESS, "VMSCAN_THROTTLE_NOPROGRESS"}, \
+ {_VMSCAN_THROTTLE_CONGESTED, "VMSCAN_THROTTLE_CONGESTED"} \
) : "VMSCAN_THROTTLE_NONE"
diff --git a/mm/vmscan.c b/mm/vmscan.c
index fb9584641ac7..700434db5735 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1021,6 +1021,39 @@ static void handle_write_error(struct address_space *mapping,
unlock_page(page);
}
+static bool skip_throttle_noprogress(pg_data_t *pgdat)
+{
+ int reclaimable = 0, write_pending = 0;
+ int i;
+
+ /*
+ * 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)
+ return true;
+
+ /*
+ * If there are a lot of dirty/writeback pages then do not
+ * throttle as throttling will occur when the pages cycle
+ * towards the end of the LRU if still under writeback.
+ */
+ for (i = 0; i < MAX_NR_ZONES; i++) {
+ struct zone *zone = pgdat->node_zones + i;
+
+ if (!populated_zone(zone))
+ continue;
+
+ reclaimable += zone_reclaimable_pages(zone);
+ write_pending += zone_page_state_snapshot(zone,
+ NR_ZONE_WRITE_PENDING);
+ }
+ if (2 * write_pending <= reclaimable)
+ return true;
+
+ return false;
+}
+
void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
{
wait_queue_head_t *wqh = &pgdat->reclaim_wait[reason];
@@ -1056,8 +1089,16 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
}
break;
+ case VMSCAN_THROTTLE_CONGESTED:
+ fallthrough;
case VMSCAN_THROTTLE_NOPROGRESS:
- timeout = HZ/2;
+ if (skip_throttle_noprogress(pgdat)) {
+ cond_resched();
+ return;
+ }
+
+ timeout = 1;
+
break;
case VMSCAN_THROTTLE_ISOLATED:
timeout = HZ/50;
@@ -3321,7 +3362,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
if (!current_is_kswapd() && current_may_throttle() &&
!sc->hibernation_mode &&
test_bit(LRUVEC_CONGESTED, &target_lruvec->flags))
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_CONGESTED);
if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
sc))
@@ -3386,16 +3427,16 @@ static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
}
/*
- * Do not throttle kswapd on NOPROGRESS as it will throttle on
- * VMSCAN_THROTTLE_WRITEBACK if there are too many pages under
- * writeback and marked for immediate reclaim at the tail of
- * the LRU.
+ * Do not throttle kswapd or cgroup reclaim on NOPROGRESS as it will
+ * throttle on VMSCAN_THROTTLE_WRITEBACK if there are too many pages
+ * under writeback and marked for immediate reclaim at the tail of the
+ * LRU.
*/
- if (current_is_kswapd())
+ if (current_is_kswapd() || cgroup_reclaim(sc))
return;
/* Throttle if making no progress at high prioities. */
- if (sc->priority < DEF_PRIORITY - 2)
+ if (sc->priority == 1 && !sc->nr_reclaimed)
reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS);
}
@@ -3415,6 +3456,7 @@ 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 +3520,19 @@ 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);
}
+ if (first_pgdat)
+ 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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