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

include/sys/ddt.h

@@ -286,14 +286,11 @@ typedef struct {
 	ddt_log_t	*ddt_log_active;	/* pointers into ddt_log */
 	ddt_log_t	*ddt_log_flushing;	/* swapped when flush starts */
 
-	hrtime_t	ddt_flush_start;	/* log flush start this txg */
-	uint32_t	ddt_flush_pass;		/* log flush pass this txg */
-
-	int32_t		ddt_flush_count;	/* entries flushed this txg */
-	int32_t		ddt_flush_min;		/* min rem entries to flush */
 	int32_t		ddt_log_ingest_rate;	/* rolling log ingest rate */
 	int32_t		ddt_log_flush_rate;	/* rolling log flush rate */
 	int32_t		ddt_log_flush_time_rate; /* avg time spent flushing */
+	uint32_t	ddt_log_flush_pressure;	/* pressure to apply for cap */
+	uint32_t	ddt_log_flush_prev_backlog; /* prev backlog size */
 
 	uint64_t	ddt_flush_force_txg;	/* flush hard before this txg */
 

include/sys/vdev.h

@@ -173,6 +173,7 @@ extern void vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority);
 extern uint32_t vdev_queue_length(vdev_t *vd);
 extern uint64_t vdev_queue_last_offset(vdev_t *vd);
 extern uint64_t vdev_queue_class_length(vdev_t *vq, zio_priority_t p);
+extern boolean_t vdev_queue_pool_busy(spa_t *spa);
 
 extern void vdev_config_dirty(vdev_t *vd);
 extern void vdev_config_clean(vdev_t *vd);

include/sys/zfs_debug.h

@@ -60,6 +60,7 @@ extern int zfs_dbgmsg_enable;
 #define	ZFS_DEBUG_METASLAB_ALLOC	(1 << 13)
 #define	ZFS_DEBUG_BRT			(1 << 14)
 #define	ZFS_DEBUG_RAIDZ_RECONSTRUCT	(1 << 15)
+#define	ZFS_DEBUG_DDT			(1 << 16)
 
 extern void __set_error(const char *file, const char *func, int line, int err);
 extern void __zfs_dbgmsg(char *buf);