block: store bdev->bd_disk->fops->submit_bio state in bdev

We have a long chain of memory dereferencing just to whether or not
this disk has a special submit_bio helper. As that's not necessarily
the common case, add a bd_has_submit_bio state in the bdev to avoid
traversing this memory dependency chain if we don't need to.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

block/bdev.c

@@ -419,6 +419,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	bdev->bd_inode = inode;
 	bdev->bd_queue = disk->queue;
 	bdev->bd_stats = alloc_percpu(struct disk_stats);
+	bdev->bd_has_submit_bio = false;
 	if (!bdev->bd_stats) {
 		iput(inode);
 		return NULL;

block/blk-core.c

@@ -587,14 +587,14 @@ static inline blk_status_t blk_check_zone_append(struct request_queue *q,
 
 static void __submit_bio(struct bio *bio)
 {
-	struct gendisk *disk = bio->bi_bdev->bd_disk;
-
 	if (unlikely(!blk_crypto_bio_prep(&bio)))
 		return;
 
-	if (!disk->fops->submit_bio) {
+	if (!bio->bi_bdev->bd_has_submit_bio) {
 		blk_mq_submit_bio(bio);
 	} else if (likely(bio_queue_enter(bio) == 0)) {
+		struct gendisk *disk = bio->bi_bdev->bd_disk;
+
 		disk->fops->submit_bio(bio);
 		blk_queue_exit(disk->queue);
 	}
@@ -698,7 +698,7 @@ void submit_bio_noacct_nocheck(struct bio *bio)
 	 */
 	if (current->bio_list)
 		bio_list_add(&current->bio_list[0], bio);
-	else if (!bio->bi_bdev->bd_disk->fops->submit_bio)
+	else if (!bio->bi_bdev->bd_has_submit_bio)
 		__submit_bio_noacct_mq(bio);
 	else
 		__submit_bio_noacct(bio);

block/genhd.c

@@ -420,6 +420,9 @@ int __must_check device_add_disk(struct device *parent, struct gendisk *disk,
 	 */
 	elevator_init_mq(disk->queue);
 
+	/* Mark bdev as having a submit_bio, if needed */
+	disk->part0->bd_has_submit_bio = disk->fops->submit_bio != NULL;
+
 	/*
 	 * If the driver provides an explicit major number it also must provide
 	 * the number of minors numbers supported, and those will be used to

include/linux/blk_types.h

@@ -47,6 +47,7 @@ struct block_device {
 	bool			bd_read_only;	/* read-only policy */
 	u8			bd_partno;
 	bool			bd_write_holder;
+	bool			bd_has_submit_bio;
 	dev_t			bd_dev;
 	atomic_t		bd_openers;
 	spinlock_t		bd_size_lock; /* for bd_inode->i_size updates */