2 files changed, 27 insertions, 8 deletions

diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index e0d44d22c1d6..815c856c0615 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -137,10 +137,21 @@ Default value: \fB8,388,608\fR.
 .sp
 .ne 2
 .na
-\fBmetaslab_debug\fR (int)
+\fBmetaslab_debug_load\fR (int)
 .ad
 .RS 12n
-Keep space maps in core to verify frees
+Load all metaslabs during pool import.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_debug_unload\fR (int)
+.ad
+.RS 12n
+Prevent metaslabs from being unloaded.
 .sp
 Use \fB1\fR for yes and \fB0\fR for no (default).
 .RE
diff --git a/module/zfs/metaslab.c b/module/zfs/metaslab.c
index 6356f79502be..32ffdfb9858d 100644
--- a/module/zfs/metaslab.c
+++ b/module/zfs/metaslab.c
@@ -81,9 +81,14 @@ int zfs_mg_alloc_failures = 0;
 int zfs_mg_noalloc_threshold = 0;
 
 /*
- * Metaslab debugging: when set, keeps all space maps in core to verify frees.
+ * When set will load all metaslabs when pool is first opened.
  */
-int metaslab_debug = 0;
+int metaslab_debug_load = 0;
+
+/*
+ * When set will prevent metaslabs from being unloaded.
+ */
+int metaslab_debug_unload = 0;
 
 /*
  * Minimum size which forces the dynamic allocator to change
@@ -846,7 +851,7 @@ metaslab_init(metaslab_group_t *mg, space_map_obj_t *smo,
 
 	metaslab_group_add(mg, msp);
 
-	if (metaslab_debug && smo->smo_object != 0) {
+	if (metaslab_debug_load && smo->smo_object != 0) {
 		mutex_enter(&msp->ms_lock);
 		VERIFY(space_map_load(msp->ms_map, mg->mg_class->mc_ops,
 		    SM_FREE, smo, spa_meta_objset(vd->vdev_spa)) == 0);
@@ -1407,7 +1412,7 @@ metaslab_sync_done(metaslab_t *msp, uint64_t txg)
 			if (msp->ms_allocmap[(txg + t) & TXG_MASK]->sm_space)
 				evictable = 0;
 
-		if (evictable && !metaslab_debug)
+		if (evictable && !metaslab_debug_unload)
 			space_map_unload(sm);
 	}
 
@@ -2109,6 +2114,9 @@ metaslab_check_free(spa_t *spa, const blkptr_t *bp)
 }
 
 #if defined(_KERNEL) && defined(HAVE_SPL)
-module_param(metaslab_debug, int, 0644);
-MODULE_PARM_DESC(metaslab_debug, "keep space maps in core to verify frees");
+module_param(metaslab_debug_load, int, 0644);
+MODULE_PARM_DESC(metaslab_debug_load, "load all metaslabs during pool import");
+
+module_param(metaslab_debug_unload, int, 0644);
+MODULE_PARM_DESC(metaslab_debug_unload, "prevent metaslabs from being unloaded");
 #endif /* _KERNEL && HAVE_SPL */