Fix infinite scan on a pool with only special allocations

Attempt to run scrub or resilver on a new pool containing only special
allocations (special vdev added on creation) caused infinite loop
because of dsl_scan_should_clear() limiting memory usage to 5% of pool
size, which it calculated accounting only normal allocation class.

Addition of special and just in case dedup classes fixes the issue.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #10106
Closes #8694
openzfs/zfs@fa130e010c2ff9b33aba11d2699b667e454b3ccb

1 files changed, 6 insertions, 3 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
index 8e73d388a945..54bd8db1cd30 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
@@ -1105,10 +1105,13 @@ scan_ds_queue_sync(dsl_scan_t *scn, dmu_tx_t *tx)
 static boolean_t
 dsl_scan_should_clear(dsl_scan_t *scn)
 {
+	spa_t *spa = scn->scn_dp->dp_spa;
 	vdev_t *rvd = scn->scn_dp->dp_spa->spa_root_vdev;
-	uint64_t mlim_hard, mlim_soft, mused;
-	uint64_t alloc = metaslab_class_get_alloc(spa_normal_class(
-	    scn->scn_dp->dp_spa));
+	uint64_t alloc, mlim_hard, mlim_soft, mused;
+
+	alloc = metaslab_class_get_alloc(spa_normal_class(spa));
+	alloc += metaslab_class_get_alloc(spa_special_class(spa));
+	alloc += metaslab_class_get_alloc(spa_dedup_class(spa));
 
 	mlim_hard = MAX((physmem / zfs_scan_mem_lim_fact) * PAGESIZE,
 	    zfs_scan_mem_lim_min);