FDT dedup log sync -- remove incremental

This PR condenses the FDT dedup log syncing into a single sync
pass. This reduces the overhead of modifying indirect blocks for the
dedup table multiple times per txg. In addition, changes were made to
the formula for how much to sync per txg. We now also consider the
backlog we have to clear, to prevent it from growing too large, or
remaining large on an idle system.

Sponsored-by: Klara, Inc.
Sponsored-by: iXsystems, Inc.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Authored-by: Don Brady <don.brady@klarasystems.com>
Authored-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Signed-off-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Closes #17038

module/zfs/vdev_queue.c

@@ -1049,6 +1049,16 @@ vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority)
 	mutex_exit(&vq->vq_lock);
 }
 
+boolean_t
+vdev_queue_pool_busy(spa_t *spa)
+{
+	dsl_pool_t *dp = spa_get_dsl(spa);
+	uint64_t min_bytes = zfs_dirty_data_max *
+	    zfs_vdev_async_write_active_min_dirty_percent / 100;
+
+	return (dp->dp_dirty_total > min_bytes);
+}
+
 /*
  * As these two methods are only used for load calculations we're not
  * concerned if we get an incorrect value on 32bit platforms due to lack of