Fix short-lived txg caused by autotrim

Current autotrim causes short-lived txg through:

1. calling txg_wait_synced() in metaslab_enable()
2. calling txg_wait_open() with should_quiesce = true

This patch addresses all the issues mentioned above.

A new cv, vdev_autotrim_kick_cv is added to kick autotrim activity.
It will be signaled once a txg is synced so that it does not change 
the original autotrim pace. Also because it is a cv, the wait is 
interruptible which speeds up the vdev_autotrim_stop_wait() call.

Finally, combining big zfs_txg_timeout, txg_wait_open() also causes
delay when exporting a pool.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: jxdking <lostking2008@hotmail.com>
Issue #8993
Closes #12194

include/sys/vdev_impl.h

@@ -329,6 +329,7 @@ struct vdev {
 	list_node_t	vdev_trim_node;
 	kmutex_t	vdev_autotrim_lock;
 	kcondvar_t	vdev_autotrim_cv;
+	kcondvar_t	vdev_autotrim_kick_cv;
 	kthread_t	*vdev_autotrim_thread;
 	/* Protects vdev_trim_thread and vdev_trim_state. */
 	kmutex_t	vdev_trim_lock;

include/sys/vdev_trim.h

@@ -41,6 +41,7 @@ extern void vdev_trim_stop_all(vdev_t *vd, vdev_trim_state_t tgt_state);
 extern void vdev_trim_stop_wait(spa_t *spa, list_t *vd_list);
 extern void vdev_trim_restart(vdev_t *vd);
 extern void vdev_autotrim(spa_t *spa);
+extern void vdev_autotrim_kick(spa_t *spa);
 extern void vdev_autotrim_stop_all(spa_t *spa);
 extern void vdev_autotrim_stop_wait(vdev_t *vd);
 extern void vdev_autotrim_restart(spa_t *spa);

module/zfs/spa.c

@@ -9449,6 +9449,9 @@ spa_sync(spa_t *spa, uint64_t txg)
 
 	spa_update_dspace(spa);
 
+	if (spa_get_autotrim(spa) == SPA_AUTOTRIM_ON)
+		vdev_autotrim_kick(spa);
+
 	/*
 	 * It had better be the case that we didn't dirty anything
 	 * since vdev_config_sync().

module/zfs/vdev.c

@@ -696,6 +696,7 @@ vdev_alloc_common(spa_t *spa, uint_t id, uint64_t guid, vdev_ops_t *ops)
 	mutex_init(&vd->vdev_trim_io_lock, NULL, MUTEX_DEFAULT, NULL);
 	cv_init(&vd->vdev_trim_cv, NULL, CV_DEFAULT, NULL);
 	cv_init(&vd->vdev_autotrim_cv, NULL, CV_DEFAULT, NULL);
+	cv_init(&vd->vdev_autotrim_kick_cv, NULL, CV_DEFAULT, NULL);
 	cv_init(&vd->vdev_trim_io_cv, NULL, CV_DEFAULT, NULL);
 
 	mutex_init(&vd->vdev_rebuild_lock, NULL, MUTEX_DEFAULT, NULL);
@@ -1148,6 +1149,7 @@ vdev_free(vdev_t *vd)
 	mutex_destroy(&vd->vdev_trim_io_lock);
 	cv_destroy(&vd->vdev_trim_cv);
 	cv_destroy(&vd->vdev_autotrim_cv);
+	cv_destroy(&vd->vdev_autotrim_kick_cv);
 	cv_destroy(&vd->vdev_trim_io_cv);
 
 	mutex_destroy(&vd->vdev_rebuild_lock);

module/zfs/vdev_trim.c

@@ -182,6 +182,25 @@ vdev_autotrim_should_stop(vdev_t *tvd)
 	    spa_get_autotrim(tvd->vdev_spa) == SPA_AUTOTRIM_OFF);
 }
 
+/*
+ * Wait for given number of kicks, return true if the wait is aborted due to
+ * vdev_autotrim_exit_wanted.
+ */
+static boolean_t
+vdev_autotrim_wait_kick(vdev_t *vd, int num_of_kick)
+{
+	mutex_enter(&vd->vdev_autotrim_lock);
+	for (int i = 0; i < num_of_kick; i++) {
+		if (vd->vdev_autotrim_exit_wanted)
+			break;
+		cv_wait(&vd->vdev_autotrim_kick_cv, &vd->vdev_autotrim_lock);
+	}
+	boolean_t exit_wanted = vd->vdev_autotrim_exit_wanted;
+	mutex_exit(&vd->vdev_autotrim_lock);
+
+	return (exit_wanted);
+}
+
 /*
  * The sync task for updating the on-disk state of a manual TRIM.  This
  * is scheduled by vdev_trim_change_state().
@@ -1190,7 +1209,6 @@ vdev_autotrim_thread(void *arg)
 
 	while (!vdev_autotrim_should_stop(vd)) {
 		int txgs_per_trim = MAX(zfs_trim_txg_batch, 1);
-		boolean_t issued_trim = B_FALSE;
 		uint64_t extent_bytes_max = zfs_trim_extent_bytes_max;
 		uint64_t extent_bytes_min = zfs_trim_extent_bytes_min;
 
@@ -1224,6 +1242,8 @@ vdev_autotrim_thread(void *arg)
 		    i += txgs_per_trim) {
 			metaslab_t *msp = vd->vdev_ms[i];
 			range_tree_t *trim_tree;
+			boolean_t issued_trim = B_FALSE;
+			boolean_t wait_aborted = B_FALSE;
 
 			spa_config_exit(spa, SCL_CONFIG, FTAG);
 			metaslab_disable(msp);
@@ -1374,7 +1394,18 @@ vdev_autotrim_thread(void *arg)
 			range_tree_vacate(trim_tree, NULL, NULL);
 			range_tree_destroy(trim_tree);
 
-			metaslab_enable(msp, issued_trim, B_FALSE);
+			/*
+			 * Wait for couples of kicks, to ensure the trim io is
+			 * synced. If the wait is aborted due to
+			 * vdev_autotrim_exit_wanted, we need to signal
+			 * metaslab_enable() to wait for sync.
+			 */
+			if (issued_trim) {
+				wait_aborted = vdev_autotrim_wait_kick(vd,
+				    TXG_CONCURRENT_STATES + TXG_DEFER_SIZE);
+			}
+
+			metaslab_enable(msp, wait_aborted, B_FALSE);
 			spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
 
 			for (uint64_t c = 0; c < children; c++) {
@@ -1388,17 +1419,14 @@ vdev_autotrim_thread(void *arg)
 			}
 
 			kmem_free(tap, sizeof (trim_args_t) * children);
+
+			if (vdev_autotrim_should_stop(vd))
+				break;
 		}
 
 		spa_config_exit(spa, SCL_CONFIG, FTAG);
 
-		/*
-		 * After completing the group of metaslabs wait for the next
-		 * open txg.  This is done to make sure that a minimum of
-		 * zfs_trim_txg_batch txgs will occur before these metaslabs
-		 * are trimmed again.
-		 */
-		txg_wait_open(spa_get_dsl(spa), 0, issued_trim);
+		vdev_autotrim_wait_kick(vd, 1);
 
 		shift++;
 		spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
@@ -1476,11 +1504,9 @@ vdev_autotrim_stop_wait(vdev_t *tvd)
 	mutex_enter(&tvd->vdev_autotrim_lock);
 	if (tvd->vdev_autotrim_thread != NULL) {
 		tvd->vdev_autotrim_exit_wanted = B_TRUE;
-
-		while (tvd->vdev_autotrim_thread != NULL) {
-			cv_wait(&tvd->vdev_autotrim_cv,
-			    &tvd->vdev_autotrim_lock);
-		}
+		cv_broadcast(&tvd->vdev_autotrim_kick_cv);
+		cv_wait(&tvd->vdev_autotrim_cv,
+		    &tvd->vdev_autotrim_lock);
 
 		ASSERT3P(tvd->vdev_autotrim_thread, ==, NULL);
 		tvd->vdev_autotrim_exit_wanted = B_FALSE;
@@ -1488,6 +1514,24 @@ vdev_autotrim_stop_wait(vdev_t *tvd)
 	mutex_exit(&tvd->vdev_autotrim_lock);
 }
 
+void
+vdev_autotrim_kick(spa_t *spa)
+{
+	ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));
+
+	vdev_t *root_vd = spa->spa_root_vdev;
+	vdev_t *tvd;
+
+	for (uint64_t i = 0; i < root_vd->vdev_children; i++) {
+		tvd = root_vd->vdev_child[i];
+
+		mutex_enter(&tvd->vdev_autotrim_lock);
+		if (tvd->vdev_autotrim_thread != NULL)
+			cv_broadcast(&tvd->vdev_autotrim_kick_cv);
+		mutex_exit(&tvd->vdev_autotrim_lock);
+	}
+}
+
 /*
  * Wait for all of the vdev_autotrim_thread associated with the pool to
  * be terminated (canceled or stopped).