[PATCH v5 3/4] dm zoned: keep polling for idle reclaim after a reclaim pass

[Kyrylo Biryuk <illofspeed@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 (and, with the
first patch of this series, when a pass fails with -ENOSPC). 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 another zone
allocation, a "reclaim" message or a resume schedules the work, 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.

When reclaim is not needed right now, make dmz_schedule_reclaim() queue
the idle poll, so the work stays queued after every pass. It uses
queue_delayed_work(), which leaves already pending work alone, so the
other callers (zone allocation and the "reclaim" message) neither
postpone a pending poll nor delay a pending immediate reclaim.

Fixes: 3b1a94c88b79 ("dm zoned: drive-managed zoned block device target")
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Assisted-by: LLM
Signed-off-by: Kyrylo Biryuk <illofspeed@gmail.com>
---
 drivers/md/dm-zoned-reclaim.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-zoned-reclaim.c b/drivers/md/dm-zoned-reclaim.c
index 88d56d3c86d..f1f9adf6039 100644
--- a/drivers/md/dm-zoned-reclaim.c
+++ b/drivers/md/dm-zoned-reclaim.c
@@ -641,7 +641,8 @@ void dmz_reclaim_bio_acc(struct dmz_reclaim *zrc)
 }
 
 /*
- * Start reclaim if necessary.
+ * Start reclaim if necessary. Otherwise make sure that an idle poll stays
+ * queued, without delaying work that is already pending.
  */
 void dmz_schedule_reclaim(struct dmz_reclaim *zrc)
 {
@@ -649,4 +650,6 @@ void dmz_schedule_reclaim(struct dmz_reclaim *zrc)
 
 	if (dmz_should_reclaim(zrc, p_unmap))
 		mod_delayed_work(zrc->wq, &zrc->work, 0);
+	else
+		queue_delayed_work(zrc->wq, &zrc->work, DMZ_IDLE_PERIOD);
 }
-- 
2.43.0