Optionally skip zil_close during zvol_create_minor_impl

If there were no zil entries to replay, skip zil_close.  zil_close waits
for a transaction to sync.  That can take several seconds, for example
during pool import of a resilvering pool.  Skipping zil_close can cut
the time for "zpool import" from 2 hours to 45 seconds on a resilvering
pool with a thousand zvols.

Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Sponsored-by: Axcient
Closes #13999 
Closes #14015

include/sys/zil.h

@@ -539,10 +539,10 @@ extern zilog_t	*zil_open(objset_t *os, zil_get_data_t *get_data,
     zil_sums_t *zil_sums);
 extern void	zil_close(zilog_t *zilog);
 
-extern void	zil_replay(objset_t *os, void *arg,
+extern boolean_t zil_replay(objset_t *os, void *arg,
     zil_replay_func_t *const replay_func[TX_MAX_TYPE]);
 extern boolean_t zil_replaying(zilog_t *zilog, dmu_tx_t *tx);
-extern void	zil_destroy(zilog_t *zilog, boolean_t keep_first);
+extern boolean_t zil_destroy(zilog_t *zilog, boolean_t keep_first);
 extern void	zil_destroy_sync(zilog_t *zilog, dmu_tx_t *tx);
 
 extern itx_t	*zil_itx_create(uint64_t txtype, size_t lrsize);

module/os/freebsd/zfs/zvol_os.c

@@ -1386,6 +1386,7 @@ zvol_os_create_minor(const char *name)
 	uint64_t volsize;
 	uint64_t volmode, hash;
 	int error;
+	bool replayed_zil = B_FALSE;
 
 	ZFS_LOG(1, "Creating ZVOL %s...", name);
 	hash = zvol_name_hash(name);
@@ -1490,11 +1491,12 @@ zvol_os_create_minor(const char *name)
 	zv->zv_zilog = zil_open(os, zvol_get_data, &zv->zv_kstat.dk_zil_sums);
 	if (spa_writeable(dmu_objset_spa(os))) {
 		if (zil_replay_disable)
-			zil_destroy(zv->zv_zilog, B_FALSE);
+			replayed_zil = zil_destroy(zv->zv_zilog, B_FALSE);
 		else
-			zil_replay(os, zv, zvol_replay_vector);
+			replayed_zil = zil_replay(os, zv, zvol_replay_vector);
 	}
-	zil_close(zv->zv_zilog);
+	if (replayed_zil)
+		zil_close(zv->zv_zilog);
 	zv->zv_zilog = NULL;
 
 	/* TODO: prefetch for geom tasting */

module/os/linux/zfs/zvol_os.c

@@ -1279,6 +1279,7 @@ zvol_os_create_minor(const char *name)
 	int error = 0;
 	int idx;
 	uint64_t hash = zvol_name_hash(name);
+	bool replayed_zil = B_FALSE;
 
 	if (zvol_inhibit_dev)
 		return (0);
@@ -1420,11 +1421,12 @@ zvol_os_create_minor(const char *name)
 	zv->zv_zilog = zil_open(os, zvol_get_data, &zv->zv_kstat.dk_zil_sums);
 	if (spa_writeable(dmu_objset_spa(os))) {
 		if (zil_replay_disable)
-			zil_destroy(zv->zv_zilog, B_FALSE);
+			replayed_zil = zil_destroy(zv->zv_zilog, B_FALSE);
 		else
-			zil_replay(os, zv, zvol_replay_vector);
+			replayed_zil = zil_replay(os, zv, zvol_replay_vector);
 	}
-	zil_close(zv->zv_zilog);
+	if (replayed_zil)
+		zil_close(zv->zv_zilog);
 	zv->zv_zilog = NULL;
 
 	/*

module/zfs/zil.c

@@ -887,8 +887,9 @@ zil_create(zilog_t *zilog)
  * txg_wait_synced() here either when keep_first is set, because both
  * zil_create() and zil_destroy() will wait for any in-progress destroys
  * to complete.
+ * Return B_TRUE if there were any entries to replay.
  */
-void
+boolean_t
 zil_destroy(zilog_t *zilog, boolean_t keep_first)
 {
 	const zil_header_t *zh = zilog->zl_header;
@@ -904,7 +905,7 @@ zil_destroy(zilog_t *zilog, boolean_t keep_first)
 	zilog->zl_old_header = *zh;		/* debugging aid */
 
 	if (BP_IS_HOLE(&zh->zh_log))
-		return;
+		return (B_FALSE);
 
 	tx = dmu_tx_create(zilog->zl_os);
 	VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
@@ -937,6 +938,8 @@ zil_destroy(zilog_t *zilog, boolean_t keep_first)
 	mutex_exit(&zilog->zl_lock);
 
 	dmu_tx_commit(tx);
+
+	return (B_TRUE);
 }
 
 void
@@ -3849,8 +3852,9 @@ zil_incr_blks(zilog_t *zilog, const blkptr_t *bp, void *arg, uint64_t claim_txg)
 
 /*
  * If this dataset has a non-empty intent log, replay it and destroy it.
+ * Return B_TRUE if there were any entries to replay.
  */
-void
+boolean_t
 zil_replay(objset_t *os, void *arg,
     zil_replay_func_t *const replay_func[TX_MAX_TYPE])
 {
@@ -3859,8 +3863,7 @@ zil_replay(objset_t *os, void *arg,
 	zil_replay_arg_t zr;
 
 	if ((zh->zh_flags & ZIL_REPLAY_NEEDED) == 0) {
-		zil_destroy(zilog, B_TRUE);
+		return (zil_destroy(zilog, B_TRUE));
-		return;
 	}
 
 	zr.zr_replay = replay_func;
@@ -3883,6 +3886,8 @@ zil_replay(objset_t *os, void *arg,
 	zil_destroy(zilog, B_FALSE);
 	txg_wait_synced(zilog->zl_dmu_pool, zilog->zl_destroy_txg);
 	zilog->zl_replay = B_FALSE;
+
+	return (B_TRUE);
 }
 
 boolean_t