blk-mq: use ->bi_bdev for I/O accounting

Remove the reverse map from a sector to a partition for I/O accounting by
simply using ->bi_bdev.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -1298,7 +1298,11 @@ void blk_account_io_start(struct request *rq)
 	if (!blk_do_io_stat(rq))
 		return;
 
-	rq->part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
+	/* passthrough requests can hold bios that do not have ->bi_bdev set */
+	if (rq->bio && rq->bio->bi_bdev)
+		rq->part = rq->bio->bi_bdev;
+	else
+		rq->part = rq->rq_disk->part0;
 
 	part_stat_lock();
 	update_io_ticks(rq->part, jiffies, false);

block/blk.h

@@ -333,8 +333,6 @@ void blk_queue_free_zone_bitmaps(struct request_queue *q);
 static inline void blk_queue_free_zone_bitmaps(struct request_queue *q) {}
 #endif
 
-struct block_device *disk_map_sector_rcu(struct gendisk *disk, sector_t sector);
-
 int blk_alloc_devt(struct block_device *part, dev_t *devt);
 void blk_free_devt(dev_t devt);
 char *disk_name(struct gendisk *hd, int partno, char *buf);

block/genhd.c

@@ -285,54 +285,6 @@ void disk_part_iter_exit(struct disk_part_iter *piter)
 }
 EXPORT_SYMBOL_GPL(disk_part_iter_exit);
 
-static inline int sector_in_part(struct block_device *part, sector_t sector)
-{
-	return part->bd_start_sect <= sector &&
-		sector < part->bd_start_sect + bdev_nr_sectors(part);
-}
-
-/**
- * disk_map_sector_rcu - map sector to partition
- * @disk: gendisk of interest
- * @sector: sector to map
- *
- * Find out which partition @sector maps to on @disk.  This is
- * primarily used for stats accounting.
- *
- * CONTEXT:
- * RCU read locked.
- *
- * RETURNS:
- * Found partition on success, part0 is returned if no partition matches
- * or the matched partition is being deleted.
- */
-struct block_device *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
-{
-	struct disk_part_tbl *ptbl;
-	struct block_device *part;
-	int i;
-
-	rcu_read_lock();
-	ptbl = rcu_dereference(disk->part_tbl);
-
-	part = rcu_dereference(ptbl->last_lookup);
-	if (part && sector_in_part(part, sector))
-		goto out_unlock;
-
-	for (i = 1; i < ptbl->len; i++) {
-		part = rcu_dereference(ptbl->part[i]);
-		if (part && sector_in_part(part, sector)) {
-			rcu_assign_pointer(ptbl->last_lookup, part);
-			goto out_unlock;
-		}
-	}
-
-	part = disk->part0;
-out_unlock:
-	rcu_read_unlock();
-	return part;
-}
-
 /**
  * disk_has_partitions
  * @disk: gendisk of interest