[PATCH 3/3] dm zoned: keep polling for idle reclaim after a reclaim pass

[illofspeed <volvo.mail@gmail.com>]

dmz_reclaim_work() re-arms its DMZ_IDLE_PERIOD poll only when
dmz_should_reclaim() returns false at the start of a pass. After a pass
it calls dmz_schedule_reclaim(), which queues the work only if reclaim
is needed right now. When a pass ends while the target is still busy and
has enough free zones, nothing is queued at all. Once the target goes
idle, nothing re-evaluates dmz_should_reclaim() until new I/O arrives or
user space sends a "reclaim" message, so the random or cache zones that
filled up under load stay full.

Seen on md RAID5 members on 27 TB host-managed drives: after heavy
writes the random zones stayed full for hours on idle targets; the
workaround was a timer sending "dmsetup message <dev> 0 reclaim". With
this patch the emptied and filled zones were reclaimed within minutes of
the targets going idle, without the timer.

After a pass, requeue the work immediately if reclaim is still needed,
otherwise re-arm the idle poll.

Fixes: 3b1a94c88b79 ("dm zoned: drive-managed zoned block device target")
Assisted-by: LLM
Signed-off-by: illofspeed <volvo.mail@gmail.com>
---
 drivers/md/dm-zoned-reclaim.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-zoned-reclaim.c b/drivers/md/dm-zoned-reclaim.c
index 2bcc163d209..7feb2628bd0 100644
--- a/drivers/md/dm-zoned-reclaim.c
+++ b/drivers/md/dm-zoned-reclaim.c
@@ -557,7 +557,16 @@ static void dmz_reclaim_work(struct work_struct *work)
 		}
 	}
 
-	dmz_schedule_reclaim(zrc);
+	/*
+	 * Keep the worker alive: when a pass ends while the target is busy
+	 * with enough free zones, dmz_schedule_reclaim() queues nothing and
+	 * the idle poll is never re-armed, so zones filled under load are not
+	 * reclaimed once the target goes idle.
+	 */
+	if (dmz_should_reclaim(zrc, dmz_reclaim_percentage(zrc)))
+		mod_delayed_work(zrc->wq, &zrc->work, 0);
+	else
+		mod_delayed_work(zrc->wq, &zrc->work, DMZ_IDLE_PERIOD);
 }
 
 /*
-- 
2.43.0