block: look up holders by bdev

Invert they way the holder relations are tracked.  This very
slightly reduces the memory overhead for partitioned devices.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210804094147.459763-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

5 files changed, 15 insertions, 17 deletions

diff --git a/block/genhd.c b/block/genhd.c
index a4817e42f3a3..cd4eab744667 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1289,7 +1289,9 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
 	disk_to_dev(disk)->type = &disk_type;
 	device_initialize(disk_to_dev(disk));
 	inc_diskseq(disk);
-
+#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
+	INIT_LIST_HEAD(&disk->slave_bdevs);
+#endif
 	return disk;
 
 out_destroy_part_tbl:
diff --git a/block/holder.c b/block/holder.c
index 960654a71342..11e65d99a9fb 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -3,7 +3,7 @@
 
 struct bd_holder_disk {
 	struct list_head	list;
-	struct gendisk		*disk;
+	struct block_device	*bdev;
 	int			refcnt;
 };
 
@@ -12,8 +12,8 @@ static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
 {
 	struct bd_holder_disk *holder;
 
-	list_for_each_entry(holder, &bdev->bd_holder_disks, list)
-		if (holder->disk == disk)
+	list_for_each_entry(holder, &disk->slave_bdevs, list)
+		if (holder->bdev == bdev)
 			return holder;
 	return NULL;
 }
@@ -61,7 +61,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	struct bd_holder_disk *holder;
 	int ret = 0;
 
-	mutex_lock(&bdev->bd_disk->open_mutex);
+	mutex_lock(&disk->open_mutex);
 
 	WARN_ON_ONCE(!bdev->bd_holder);
 
@@ -82,7 +82,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	}
 
 	INIT_LIST_HEAD(&holder->list);
-	holder->disk = disk;
+	holder->bdev = bdev;
 	holder->refcnt = 1;
 
 	ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
@@ -93,7 +93,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	if (ret)
 		goto out_del;
 
-	list_add(&holder->list, &bdev->bd_holder_disks);
+	list_add(&holder->list, &disk->slave_bdevs);
 	goto out_unlock;
 
 out_del:
@@ -101,7 +101,7 @@ out_del:
 out_free:
 	kfree(holder);
 out_unlock:
-	mutex_unlock(&bdev->bd_disk->open_mutex);
+	mutex_unlock(&disk->open_mutex);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(bd_link_disk_holder);
@@ -120,7 +120,7 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 {
 	struct bd_holder_disk *holder;
 
-	mutex_lock(&bdev->bd_disk->open_mutex);
+	mutex_lock(&disk->open_mutex);
 	holder = bd_find_holder_disk(bdev, disk);
 	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
 		del_symlink(disk->slave_dir, bdev_kobj(bdev));
@@ -128,6 +128,6 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 		list_del_init(&holder->list);
 		kfree(holder);
 	}
-	mutex_unlock(&bdev->bd_disk->open_mutex);
+	mutex_unlock(&disk->open_mutex);
 }
 EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index ae9651cad923..cc801767a377 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -902,9 +902,6 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	bdev->bd_disk = disk;
 	bdev->bd_partno = partno;
 	bdev->bd_inode = inode;
-#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
-	INIT_LIST_HEAD(&bdev->bd_holder_disks);
-#endif
 	bdev->bd_stats = alloc_percpu(struct disk_stats);
 	if (!bdev->bd_stats) {
 		iput(inode);
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 7a4e139d24ef..e92735655684 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -34,9 +34,6 @@ struct block_device {
 	void *			bd_holder;
 	int			bd_holders;
 	bool			bd_write_holder;
-#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
-	struct list_head	bd_holder_disks;
-#endif
 	struct kobject		*bd_holder_dir;
 	u8			bd_partno;
 	spinlock_t		bd_size_lock; /* for bd_inode->i_size updates */
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index e21a91c16a79..0721807d76ee 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -159,7 +159,9 @@ struct gendisk {
 	unsigned open_partitions;	/* number of open partitions */
 
 	struct kobject *slave_dir;
-
+#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
+	struct list_head slave_bdevs;
+#endif
 	struct timer_rand_state *random;
 	atomic_t sync_io;		/* RAID */
 	struct disk_events *ev;