[PATCH v3 5/9] null_blk: Improve implicit zone close

[Damien Le Moal <damien.lemoal@xxxxxxx>]

When open zone resource management is enabled, that is, when a null_blk
zoned device is created with zone_max_open different than 0, implicitly
or explicitly opening a zone may require implicitly closing a zone
that is already implicitly open. This operation is done using the
function null_close_first_imp_zone(), which search for an implicitly
open zone to close starting from the first sequential zone. This
implementation is simple but may result in the same being constantly
implicitly closed and then implicitly reopened on write, namely, the
lowest numbered zone that is being written.

Avoid this by starting the search for an implicitly open zone starting
from the zone following the last zone that was implicitly closed. The
function null_close_first_imp_zone() is renamed
null_close_imp_open_zone().

Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
 drivers/block/null_blk.h       |  1 +
 drivers/block/null_blk_zoned.c | 22 +++++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h
index 14546ead1d66..29a8817fadfc 100644
--- a/drivers/block/null_blk.h
+++ b/drivers/block/null_blk.h
@@ -67,6 +67,7 @@ struct nullb_device {
 	unsigned int nr_zones_imp_open;
 	unsigned int nr_zones_exp_open;
 	unsigned int nr_zones_closed;
+	unsigned int imp_close_zone_no;
 	struct nullb_zone *zones;
 	sector_t zone_size_sects;
 	bool need_zone_res_mgmt;
diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
index 2c746221e8e6..cd773af5f186 100644
--- a/drivers/block/null_blk_zoned.c
+++ b/drivers/block/null_blk_zoned.c
@@ -115,6 +115,7 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
 		pr_info("zone_max_open limit disabled, limit >= zone count\n");
 	}
 	dev->need_zone_res_mgmt = dev->zone_max_active || dev->zone_max_open;
+	dev->imp_close_zone_no = dev->zone_nr_conv;
 
 	for (i = 0; i <  dev->zone_nr_conv; i++) {
 		zone = &dev->zones[i];
@@ -275,13 +276,24 @@ static blk_status_t __null_close_zone(struct nullb_device *dev,
 	return BLK_STS_OK;
 }
 
-static void null_close_first_imp_zone(struct nullb_device *dev)
+static void null_close_imp_open_zone(struct nullb_device *dev)
 {
-	unsigned int i;
+	struct nullb_zone *zone;
+	unsigned int zno, i;
+
+	zno = dev->imp_close_zone_no;
+	if (zno >= dev->nr_zones)
+		zno = dev->zone_nr_conv;
 
 	for (i = dev->zone_nr_conv; i < dev->nr_zones; i++) {
-		if (dev->zones[i].cond == BLK_ZONE_COND_IMP_OPEN) {
-			__null_close_zone(dev, &dev->zones[i]);
+		zone = &dev->zones[zno];
+		zno++;
+		if (zno >= dev->nr_zones)
+			zno = dev->zone_nr_conv;
+
+		if (zone->cond == BLK_ZONE_COND_IMP_OPEN) {
+			__null_close_zone(dev, zone);
+			dev->imp_close_zone_no = zno;
 			return;
 		}
 	}
@@ -309,7 +321,7 @@ static blk_status_t null_check_open(struct nullb_device *dev)
 
 	if (dev->nr_zones_imp_open) {
 		if (null_check_active(dev) == BLK_STS_OK) {
-			null_close_first_imp_zone(dev);
+			null_close_imp_open_zone(dev);
 			return BLK_STS_OK;
 		}
 	}
-- 
2.26.2