[PATCH v3 10/30] block: Fake max open zones limit when there is no limit

[Damien Le Moal]

For a zoned block device that has no limit on the number of open zones
and no limit on the number of active zones, the zone write plug free
list is initialized with 128 zone write plugs. For such case, set the
device max_open_zones queue limit to this value to indicate to the user
the potential performance penalty that may happen when writing
simultaneously to more zones than the free list size.

Signed-off-by: Damien Le Moal <dlemoal at kernel.org>
---
 block/blk-zoned.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 3084dae5408e..8ad5d271d3f8 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -1570,17 +1570,24 @@ static int disk_revalidate_zone_resources(struct gendisk *disk,
 {
 	struct queue_limits *lim = &disk->queue->limits;
 	unsigned int max_nr_zwplugs;
+	bool set_max_open = false;
 	int ret;
 
 	/*
 	 * If the device has no limit on the maximum number of open and active
 	 * zones, use BLK_ZONE_DEFAULT_MAX_NR_WPLUGS for the maximum number
-	 * of zone write plugs to hash.
+	 * of zone write plugs to hash and set the max_open_zones queue limit
+	 * of the device to indicate to the user the number of pre-allocated
+	 * zone write plugsso that the user is aware of the potential
+	 * performance penalty for simultaneously writing to more zones than
+	 * this limit.
 	 */
 	max_nr_zwplugs = max(lim->max_open_zones, lim->max_active_zones);
-	if (!max_nr_zwplugs)
+	if (!max_nr_zwplugs) {
 		max_nr_zwplugs =
 			min(BLK_ZONE_DEFAULT_MAX_NR_WPLUGS, nr_zones);
+		set_max_open = true;
+	}
 
 	if (!disk->zone_wplugs_hash) {
 		ret = disk_alloc_zone_resources(disk, max_nr_zwplugs);
@@ -1596,6 +1603,9 @@ static int disk_revalidate_zone_resources(struct gendisk *disk,
 			return ret;
 	}
 
+	if (set_max_open)
+		disk_set_max_open_zones(disk, max_nr_zwplugs);
+
 	return 0;
 }
 
-- 
2.44.0