MFC r272504: MFV r272494:

Make space_map_truncate() always do space_map_reallocate().  Without
this, setting space_map_max_blksz would cause panic for existing pool,
as dmu_objset_set_blocksize would fail if the object have multiple blocks.

Illumos issues:
   5164 space_map_max_blksz causes panic, does not work
   5165 zdb fails assertion when run on pool with recently-enabled
	spacemap_histogram feature

1 files changed, 16 insertions, 8 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
index 2fe067b..dc15b3e 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
@@ -77,7 +77,7 @@ SYSCTL_INT(_vfs_zfs, OID_AUTO, condense_pct, CTLFLAG_RWTUN,
 /*
  * Condensing a metaslab is not guaranteed to actually reduce the amount of
  * space used on disk. In particular, a space map uses data in increments of
- * MAX(1 << ashift, SPACE_MAP_INITIAL_BLOCKSIZE), so a metaslab might use the
+ * MAX(1 << ashift, space_map_blksize), so a metaslab might use the
  * same number of blocks after condensing. Since the goal of condensing is to
  * reduce the number of IOPs required to read the space map, we only want to
  * condense when we can be sure we will reduce the number of blocks used by the
@@ -1491,10 +1491,12 @@ metaslab_fragmentation(metaslab_t *msp)
 		uint64_t txg = spa_syncing_txg(spa);
 		vdev_t *vd = msp->ms_group->mg_vd;
 
-		msp->ms_condense_wanted = B_TRUE;
-		vdev_dirty(vd, VDD_METASLAB, msp, txg + 1);
-		spa_dbgmsg(spa, "txg %llu, requesting force condense: "
-		    "msp %p, vd %p", txg, msp, vd);
+		if (spa_writeable(spa)) {
+			msp->ms_condense_wanted = B_TRUE;
+			vdev_dirty(vd, VDD_METASLAB, msp, txg + 1);
+			spa_dbgmsg(spa, "txg %llu, requesting force condense: "
+			    "msp %p, vd %p", txg, msp, vd);
+		}
 		return (ZFS_FRAG_INVALID);
 	}
 
@@ -1938,6 +1940,15 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
 
 	mutex_enter(&msp->ms_lock);
 
+	/*
+	 * Note: metaslab_condense() clears the space_map's histogram.
+	 * Therefore we must verify and remove this histogram before
+	 * condensing.
+	 */
+	metaslab_group_histogram_verify(mg);
+	metaslab_class_histogram_verify(mg->mg_class);
+	metaslab_group_histogram_remove(mg, msp);
+
 	if (msp->ms_loaded && spa_sync_pass(spa) == 1 &&
 	    metaslab_should_condense(msp)) {
 		metaslab_condense(msp, txg, tx);
@@ -1946,9 +1957,6 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
 		space_map_write(msp->ms_sm, *freetree, SM_FREE, tx);
 	}
 
-	metaslab_group_histogram_verify(mg);
-	metaslab_class_histogram_verify(mg->mg_class);
-	metaslab_group_histogram_remove(mg, msp);
 	if (msp->ms_loaded) {
 		/*
 		 * When the space map is loaded, we have an accruate