block: Fake max open zones limit when there is no limit

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 mempool
is created with a size of 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 mempool size.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>
Tested-by: Dennis Maisenbacher <dennis.maisenbacher@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240408014128.205141-9-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-zoned.c

@@ -1503,6 +1503,38 @@ struct blk_revalidate_zone_args {
 	sector_t	sector;
 };
 
+/*
+ * Update the disk zone resources information and device queue limits.
+ * The disk queue is frozen when this is executed.
+ */
+static int disk_update_zone_resources(struct gendisk *disk,
+				      struct blk_revalidate_zone_args *args)
+{
+	struct request_queue *q = disk->queue;
+	struct queue_limits lim;
+
+	disk->nr_zones = args->nr_zones;
+	disk->zone_capacity = args->zone_capacity;
+	swap(disk->seq_zones_wlock, args->seq_zones_wlock);
+	swap(disk->conv_zones_bitmap, args->conv_zones_bitmap);
+
+	/*
+	 * If the device has no limit on the maximum number of open and active
+	 * zones, set its max open zone limit to the mempool size to indicate
+	 * to the user that there is a potential performance impact due to
+	 * dynamic zone write plug allocation when simultaneously writing to
+	 * more zones than the size of the mempool.
+	 */
+	if (disk->zone_wplugs_pool) {
+		lim = queue_limits_start_update(q);
+		if (!lim.max_open_zones && !lim.max_active_zones)
+			lim.max_open_zones = disk->zone_wplugs_pool->min_nr;
+		return queue_limits_commit_update(q, &lim);
+	}
+
+	return 0;
+}
+
 /*
  * Helper function to check the validity of zones of a zoned block device.
  */
@@ -1703,17 +1735,14 @@ int blk_revalidate_disk_zones(struct gendisk *disk,
 	 */
 	blk_mq_freeze_queue(q);
 	if (ret > 0) {
-		disk->nr_zones = args.nr_zones;
-		disk->zone_capacity = args.zone_capacity;
-		swap(disk->seq_zones_wlock, args.seq_zones_wlock);
-		swap(disk->conv_zones_bitmap, args.conv_zones_bitmap);
+		ret = disk_update_zone_resources(disk, &args);
 		if (update_driver_data)
 			update_driver_data(disk);
-		ret = 0;
 	} else {
 		pr_warn("%s: failed to revalidate zones\n", disk->disk_name);
-		disk_free_zone_resources(disk);
 	}
+	if (ret)
+		disk_free_zone_resources(disk);
 	blk_mq_unfreeze_queue(q);
 
 	kfree(args.seq_zones_wlock);