Re: [PATCH 6/7] btrfs: drop extent_io_ops::merge_bio_hook callback

[Nikolay Borisov <nborisov@suse.com>]

On 19.07.2018 14:05, David Sterba wrote:
> The data and metadata callback implementation both use the same
> function. We can remove the call indirection completely.
> 
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/compression.c | 10 +++-------
>  fs/btrfs/disk-io.c     |  2 --
>  fs/btrfs/extent_io.c   |  4 ++--
>  fs/btrfs/extent_io.h   |  3 ---
>  fs/btrfs/inode.c       |  5 ++---
>  5 files changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index 70dace47258b..9bfa66592aa7 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -299,7 +299,6 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  	struct bio *bio = NULL;
>  	struct compressed_bio *cb;
>  	unsigned long bytes_left;
> -	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
>  	int pg_index = 0;
>  	struct page *page;
>  	u64 first_byte = disk_start;
> @@ -338,9 +337,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  		page = compressed_pages[pg_index];
>  		page->mapping = inode->i_mapping;
>  		if (bio->bi_iter.bi_size)
> -			submit = io_tree->ops->merge_bio_hook(page, 0,
> -							   PAGE_SIZE,
> -							   bio, 0);
> +			submit = btrfs_merge_bio_hook(page, 0, PAGE_SIZE, bio, 0);
>  
>  		page->mapping = NULL;
>  		if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) <
> @@ -622,9 +619,8 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>  		page->index = em_start >> PAGE_SHIFT;
>  
>  		if (comp_bio->bi_iter.bi_size)
> -			submit = tree->ops->merge_bio_hook(page, 0,
> -							PAGE_SIZE,
> -							comp_bio, 0);
> +			submit = btrfs_merge_bio_hook(page, 0, PAGE_SIZE,
> +					comp_bio, 0);
>  
>  		page->mapping = NULL;
>  		if (submit || bio_add_page(comp_bio, page, PAGE_SIZE, 0) <
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index d6c04933abbc..31ab764cf4e3 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -4527,8 +4527,6 @@ static const struct extent_io_ops btree_extent_io_ops = {
>  	/* mandatory callbacks */
>  	.submit_bio_hook = btree_submit_bio_hook,
>  	.readpage_end_io_hook = btree_readpage_end_io_hook,
> -	/* note we're sharing with inode.c for the merge bio hook */
> -	.merge_bio_hook = btrfs_merge_bio_hook,
>  	.readpage_io_failed_hook = btree_io_failed_hook,
>  	.set_range_writeback = btrfs_set_range_writeback,
>  
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index f7a138278f16..55a845621f85 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -2784,8 +2784,8 @@ static int submit_extent_page(unsigned int opf, struct extent_io_tree *tree,
>  		else
>  			contig = bio_end_sector(bio) == sector;
>  
> -		if (tree->ops && tree->ops->merge_bio_hook(page, offset,
> -					page_size, bio, bio_flags))
> +		if (tree->ops && btrfs_merge_bio_hook(page, offset, page_size,
> +						      bio, bio_flags))

While this is correct I dislike having the if (tree->ops ) check. So
under what conditions do we NOT have the tree->ops set? Looking at the
code it seems we are setting it everytime we create an inode in
btrfs_create. We also set it for symlinks (btrfs_symlink) and a tmp file
(btrfs_tmpfile). Strangely enough in btrfs_read_locked_inode we only set
it for regular files (S_IFREG).

submit_extent_page seems to be called for both metadata but as we no
longer distinguish between eb merge_hook and data merge_hook perhaps the
tree->ops could be killed as well ?

>  			can_merge = false;
>  
>  		if (prev_bio_flags != bio_flags || !contig || !can_merge ||
> diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
> index 6edbe01fd09d..ec7c4a2982d0 100644
> --- a/fs/btrfs/extent_io.h
> +++ b/fs/btrfs/extent_io.h
> @@ -101,9 +101,6 @@ struct extent_io_ops {
>  	int (*readpage_end_io_hook)(struct btrfs_io_bio *io_bio, u64 phy_offset,
>  				    struct page *page, u64 start, u64 end,
>  				    int mirror);
> -	int (*merge_bio_hook)(struct page *page, unsigned long offset,
> -			      size_t size, struct bio *bio,
> -			      unsigned long bio_flags);
>  	int (*readpage_io_failed_hook)(struct page *page, int failed_mirror);
>  	void (*set_range_writeback)(void *private_data, u64 start, u64 end);
>  
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 1614551cf953..845621a71468 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1893,8 +1893,8 @@ static void btrfs_clear_bit_hook(void *private_data,
>  }
>  
>  /*
> - * extent_io.c merge_bio_hook, this must check the chunk tree to make sure
> - * we don't create bios that span stripes or chunks
> + * Merge bio hook, this must check the chunk tree to make sure we don't create
> + * bios that span stripes or chunks
>   *
>   * return 1 if page cannot be merged to bio
>   * return 0 if page can be merged to bio
> @@ -10540,7 +10540,6 @@ static const struct extent_io_ops btrfs_extent_io_ops = {
>  	/* mandatory callbacks */
>  	.submit_bio_hook = btrfs_submit_bio_hook,
>  	.readpage_end_io_hook = btrfs_readpage_end_io_hook,
> -	.merge_bio_hook = btrfs_merge_bio_hook,
>  	.readpage_io_failed_hook = btrfs_readpage_io_failed_hook,
>  	.set_range_writeback = btrfs_set_range_writeback,
>  
>