[PATCH v5 1/4] dm zoned: back off when reclaim finds no destination zone

[Kyrylo Biryuk <illofspeed@gmail.com>]

When dmz_do_reclaim() fails with -ENOSPC because no free zone is
available to copy the data into, dmz_reclaim_work() still ends with
dmz_schedule_reclaim(). If the target is idle, dmz_should_reclaim()
keeps returning true, the work is queued again with no delay and the
worker spins on the same failing pass.

Re-arm the idle poll instead, so that reclaim is retried after
DMZ_IDLE_PERIOD. The next patch makes -ENOSPC the expected result when
an idle target has random zones but no free sequential zone.

Tested on 7.3-rc7 together with the next two patches, on emulated
host-managed drives (scsi_debug zbc=managed, and the tcmu-runner ZBC
handler under md RAID5). Earlier versions of the series ran on 7.2.6 on
three 27 TB host-managed drives used as md RAID5 members.

Fixes: 3b1a94c88b79 ("dm zoned: drive-managed zoned block device target")
Reviewed-by: Hannes Reinecke <hare@kernel.org>
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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/md/dm-zoned-reclaim.c b/drivers/md/dm-zoned-reclaim.c
index c041413c729..315f0da99f3 100644
--- a/drivers/md/dm-zoned-reclaim.c
+++ b/drivers/md/dm-zoned-reclaim.c
@@ -540,6 +540,14 @@ static void dmz_reclaim_work(struct work_struct *work)
 	if (ret && ret != -EINTR) {
 		if (!dmz_check_dev(zmd))
 			return;
+		if (ret == -ENOSPC) {
+			/*
+			 * No zone to copy into: nothing can progress now.
+			 * Rescheduling immediately would spin; poll instead.
+			 */
+			mod_delayed_work(zrc->wq, &zrc->work, DMZ_IDLE_PERIOD);
+			return;
+		}
 	}
 
 	dmz_schedule_reclaim(zrc);
-- 
2.43.0