[PATCH v2 2/2] ext2, ext4: use the super_block dax_device

[Dan Williams <dan.j.williams@xxxxxxxxx>]

The ->iomap_begin() operation is a hot path, and now that mount_bdev()
arranges for the dax_device to be populated in the super_block, we can
just reference that attribute directly rather than perform a new lookup.

Cc: Jan Kara <jack@xxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Reported-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 fs/ext2/inode.c |   10 ++--------
 fs/ext4/inode.c |   10 ++--------
 2 files changed, 4 insertions(+), 16 deletions(-)

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 30163d007b2f..7102b77a83c6 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -800,7 +800,6 @@ int ext2_get_block(struct inode *inode, sector_t iblock,
 static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		unsigned flags, struct iomap *iomap)
 {
-	struct block_device *bdev;
 	unsigned int blkbits = inode->i_blkbits;
 	unsigned long first_block = offset >> blkbits;
 	unsigned long max_blocks = (length + (1 << blkbits) - 1) >> blkbits;
@@ -814,13 +813,9 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		return ret;
 
 	iomap->flags = 0;
-	bdev = inode->i_sb->s_bdev;
-	iomap->bdev = bdev;
+	iomap->bdev = inode->i_sb->s_bdev;
 	iomap->offset = (u64)first_block << blkbits;
-	if (blk_queue_dax(bdev->bd_queue))
-		iomap->dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
-	else
-		iomap->dax_dev = NULL;
+	iomap->dax_dev = inode->i_sb->s_daxdev;
 
 	if (ret == 0) {
 		iomap->type = IOMAP_HOLE;
@@ -842,7 +837,6 @@ static int
 ext2_iomap_end(struct inode *inode, loff_t offset, loff_t length,
 		ssize_t written, unsigned flags, struct iomap *iomap)
 {
-	fs_put_dax(iomap->dax_dev);
 	if (iomap->type == IOMAP_MAPPED &&
 	    written < length &&
 	    (flags & IOMAP_WRITE))
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c774bdc22759..311690522366 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3404,7 +3404,6 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
 static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			    unsigned flags, struct iomap *iomap)
 {
-	struct block_device *bdev;
 	unsigned int blkbits = inode->i_blkbits;
 	unsigned long first_block = offset >> blkbits;
 	unsigned long last_block = (offset + length - 1) >> blkbits;
@@ -3473,12 +3472,8 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	}
 
 	iomap->flags = 0;
-	bdev = inode->i_sb->s_bdev;
-	iomap->bdev = bdev;
-	if (blk_queue_dax(bdev->bd_queue))
-		iomap->dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
-	else
-		iomap->dax_dev = NULL;
+	iomap->bdev = inode->i_sb->s_bdev;
+	iomap->dax_dev = inode->i_sb->s_daxdev;
 	iomap->offset = first_block << blkbits;
 
 	if (ret == 0) {
@@ -3511,7 +3506,6 @@ static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
 	int blkbits = inode->i_blkbits;
 	bool truncate = false;
 
-	fs_put_dax(iomap->dax_dev);
 	if (!(flags & IOMAP_WRITE) || (flags & IOMAP_FAULT))
 		return 0;