dm mpath: optimize NVMe bio-based support

All code that deals with pg_init is not used with bio-based NVMe mode.
This includes skipping initialization of pg_init related variables.

Also, pg_init related members on 'struct multipath' have been grouped
together.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -64,36 +64,30 @@ struct priority_group {
 
 /* Multipath context */
 struct multipath {
-	struct list_head list;
-	struct dm_target *ti;
-
-	const char *hw_handler_name;
-	char *hw_handler_params;
+	unsigned long flags;		/* Multipath state flags */
 
 	spinlock_t lock;
-
-	unsigned nr_priority_groups;
-	struct list_head priority_groups;
-
-	wait_queue_head_t pg_init_wait;	/* Wait for pg_init completion */
+	enum dm_queue_mode queue_mode;
 
 	struct pgpath *current_pgpath;
 	struct priority_group *current_pg;
 	struct priority_group *next_pg;	/* Switch to this PG if set */
 
-	unsigned long flags;		/* Multipath state flags */
+	atomic_t nr_valid_paths;	/* Total number of usable paths */
+	unsigned nr_priority_groups;
+	struct list_head priority_groups;
 
+	const char *hw_handler_name;
+	char *hw_handler_params;
+	wait_queue_head_t pg_init_wait;	/* Wait for pg_init completion */
 	unsigned pg_init_retries;	/* Number of times to retry pg_init */
 	unsigned pg_init_delay_msecs;	/* Number of msecs before pg_init retry */
-
-	atomic_t nr_valid_paths;	/* Total number of usable paths */
 	atomic_t pg_init_in_progress;	/* Only one pg_init allowed at once */
 	atomic_t pg_init_count;		/* Number of times pg_init called */
 
-	enum dm_queue_mode queue_mode;
-
 	struct mutex work_mutex;
 	struct work_struct trigger_event;
+	struct dm_target *ti;
 
 	struct work_struct process_queued_bios;
 	struct bio_list queued_bios;
@@ -135,10 +129,10 @@ static struct pgpath *alloc_pgpath(void)
 {
 	struct pgpath *pgpath = kzalloc(sizeof(*pgpath), GFP_KERNEL);
 
-	if (pgpath) {
+	if (!pgpath)
+		return NULL;
+
 	pgpath->is_active = true;
-		INIT_DELAYED_WORK(&pgpath->activate_path, activate_path_work);
-	}
 
 	return pgpath;
 }
@@ -193,13 +187,8 @@ static struct multipath *alloc_multipath(struct dm_target *ti)
 	if (m) {
 		INIT_LIST_HEAD(&m->priority_groups);
 		spin_lock_init(&m->lock);
-		set_bit(MPATHF_QUEUE_IO, &m->flags);
 		atomic_set(&m->nr_valid_paths, 0);
-		atomic_set(&m->pg_init_in_progress, 0);
-		atomic_set(&m->pg_init_count, 0);
-		m->pg_init_delay_msecs = DM_PG_INIT_DELAY_DEFAULT;
 		INIT_WORK(&m->trigger_event, trigger_event);
-		init_waitqueue_head(&m->pg_init_wait);
 		mutex_init(&m->work_mutex);
 
 		m->queue_mode = DM_TYPE_NONE;
@@ -235,6 +224,14 @@ static int alloc_multipath_stage2(struct dm_target *ti, struct multipath *m)
 		}
 	}
 
+	if (m->queue_mode != DM_TYPE_NVME_BIO_BASED) {
+		set_bit(MPATHF_QUEUE_IO, &m->flags);
+		atomic_set(&m->pg_init_in_progress, 0);
+		atomic_set(&m->pg_init_count, 0);
+		m->pg_init_delay_msecs = DM_PG_INIT_DELAY_DEFAULT;
+		init_waitqueue_head(&m->pg_init_wait);
+	}
+
 	dm_table_set_type(ti->table, m->queue_mode);
 
 	return 0;
@@ -339,6 +336,9 @@ static void __switch_pg(struct multipath *m, struct priority_group *pg)
 {
 	m->current_pg = pg;
 
+	if (m->queue_mode == DM_TYPE_NVME_BIO_BASED)
+		return;
+
 	/* Must we initialise the PG first, and queue I/O till it's ready? */
 	if (m->hw_handler_name) {
 		set_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);
@@ -384,6 +384,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
 	unsigned bypassed = 1;
 
 	if (!atomic_read(&m->nr_valid_paths)) {
+		if (m->queue_mode != DM_TYPE_NVME_BIO_BASED)
 			clear_bit(MPATHF_QUEUE_IO, &m->flags);
 		goto failed;
 	}
@@ -528,8 +529,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
 	clone = blk_get_request(q, rq->cmd_flags | REQ_NOMERGE, GFP_ATOMIC);
 	if (IS_ERR(clone)) {
 		/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
-		bool queue_dying = blk_queue_dying(q);
-		if (queue_dying) {
+		if (blk_queue_dying(q)) {
 			atomic_inc(&m->pg_init_in_progress);
 			activate_or_offline_path(pgpath);
 		}
@@ -563,21 +563,28 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
 
 	/* Do we need to select a new pgpath? */
 	pgpath = READ_ONCE(m->current_pgpath);
+	/* MPATHF_QUEUE_IO will never be set for NVMe */
 	queue_io = test_bit(MPATHF_QUEUE_IO, &m->flags);
 	if (!pgpath || !queue_io)
 		pgpath = choose_pgpath(m, mpio->nr_bytes);
 
-	if ((pgpath && queue_io) ||
-	    (!pgpath && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))) {
+	if ((!pgpath && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) ||
+	    (pgpath && queue_io)) {
 		/* Queue for the daemon to resubmit */
 		spin_lock_irqsave(&m->lock, flags);
 		bio_list_add(&m->queued_bios, bio);
 		spin_unlock_irqrestore(&m->lock, flags);
+
+		if (m->queue_mode == DM_TYPE_NVME_BIO_BASED) {
+			queue_work(kmultipathd, &m->process_queued_bios);
+		} else {
 			/* PG_INIT_REQUIRED cannot be set without QUEUE_IO */
 			if (queue_io || test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags))
 				pg_init_all_paths(m);
 			else if (!queue_io)
 				queue_work(kmultipathd, &m->process_queued_bios);
+		}
+
 		return DM_MAPIO_SUBMITTED;
 	}
 
@@ -750,34 +757,11 @@ static int parse_path_selector(struct dm_arg_set *as, struct priority_group *pg,
 	return 0;
 }
 
-static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps,
-			       struct dm_target *ti)
+static int setup_scsi_dh(struct block_device *bdev, struct multipath *m, char **error)
 {
-	int r;
-	struct pgpath *p;
-	struct multipath *m = ti->private;
-	struct request_queue *q = NULL;
+	struct request_queue *q = bdev_get_queue(bdev);
 	const char *attached_handler_name;
-
-	/* we need at least a path arg */
-	if (as->argc < 1) {
-		ti->error = "no device given";
-		return ERR_PTR(-EINVAL);
-	}
-
-	p = alloc_pgpath();
-	if (!p)
-		return ERR_PTR(-ENOMEM);
-
-	r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
-			  &p->path.dev);
-	if (r) {
-		ti->error = "error getting device";
-		goto bad;
-	}
-
-	if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags) || m->hw_handler_name)
-		q = bdev_get_queue(p->path.dev->bdev);
+	int r;
 
 	if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags)) {
 retain:
@@ -809,23 +793,56 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 			char b[BDEVNAME_SIZE];
 
 			printk(KERN_INFO "dm-mpath: retaining handler on device %s\n",
-				bdevname(p->path.dev->bdev, b));
+			       bdevname(bdev, b));
 			goto retain;
 		}
 		if (r < 0) {
-			ti->error = "error attaching hardware handler";
-			dm_put_device(ti, p->path.dev);
-			goto bad;
+			*error = "error attaching hardware handler";
+			return r;
 		}
 
 		if (m->hw_handler_params) {
 			r = scsi_dh_set_params(q, m->hw_handler_params);
 			if (r < 0) {
-				ti->error = "unable to set hardware "
-							"handler parameters";
-				dm_put_device(ti, p->path.dev);
+				*error = "unable to set hardware handler parameters";
+				return r;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps,
+				 struct dm_target *ti)
+{
+	int r;
+	struct pgpath *p;
+	struct multipath *m = ti->private;
+
+	/* we need at least a path arg */
+	if (as->argc < 1) {
+		ti->error = "no device given";
+		return ERR_PTR(-EINVAL);
+	}
+
+	p = alloc_pgpath();
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
+			  &p->path.dev);
+	if (r) {
+		ti->error = "error getting device";
 		goto bad;
 	}
+
+	if (m->queue_mode != DM_TYPE_NVME_BIO_BASED) {
+		INIT_DELAYED_WORK(&p->activate_path, activate_path_work);
+		r = setup_scsi_dh(p->path.dev->bdev, m, &ti->error);
+		if (r) {
+			dm_put_device(ti, p->path.dev);
+			goto bad;
 		}
 	}
 
@@ -836,7 +853,6 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 	}
 
 	return p;
-
  bad:
 	free_pgpath(p);
 	return ERR_PTR(r);
@@ -1152,16 +1168,19 @@ static void multipath_wait_for_pg_init_completion(struct multipath *m)
 
 static void flush_multipath_work(struct multipath *m)
 {
+	if (m->hw_handler_name) {
 		set_bit(MPATHF_PG_INIT_DISABLED, &m->flags);
 		smp_mb__after_atomic();
 
 		flush_workqueue(kmpath_handlerd);
 		multipath_wait_for_pg_init_completion(m);
-	flush_workqueue(kmultipathd);
-	flush_work(&m->trigger_event);
 
 		clear_bit(MPATHF_PG_INIT_DISABLED, &m->flags);
 		smp_mb__after_atomic();
+	}
+
+	flush_workqueue(kmultipathd);
+	flush_work(&m->trigger_event);
 }
 
 static void multipath_dtr(struct dm_target *ti)