Re: [PATCH 06/11] btrfs: simplify btrfs_split_ordered_extent

[Naohiro Aota <Naohiro.Aota@wdc.com>]

On Fri, Mar 24, 2023 at 10:32:02AM +0800, Christoph Hellwig wrote:
> btrfs_split_ordered_extent is only ever asked to split out the beginning
> of an ordered_extent.  Change it to only take a len to split out, and
> switch it to allocate the new extent for the beginning, as that helps
> with callers that want to keep a pointer to the ordered_extent that
> it is stealing from.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/btrfs/inode.c        |  8 +-------
>  fs/btrfs/ordered-data.c | 28 ++++++++++++----------------
>  fs/btrfs/ordered-data.h |  3 +--
>  3 files changed, 14 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 2cbc6c316effc1..bff23bac85f2ef 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -2646,17 +2646,11 @@ blk_status_t btrfs_extract_ordered_extent(struct btrfs_bio *bbio)
>  		goto out;
>  	}
>  
> -	/* The bio must be entirely covered by the ordered extent */
> -	if (WARN_ON_ONCE(len > ordered_len)) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> -
>  	/* No need to split if the ordered extent covers the entire bio */
>  	if (ordered->disk_num_bytes == len)
>  		goto out;
>  
> -	ret = btrfs_split_ordered_extent(ordered, len, 0);
> +	ret = btrfs_split_ordered_extent(ordered, len);
>  	if (ret)
>  		goto out;
>  	ret = split_zoned_em(inode, bbio->file_offset, ordered_len, len, 0);
> diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
> index 4b46406c0c8af5..1d5971b6e68c66 100644
> --- a/fs/btrfs/ordered-data.c
> +++ b/fs/btrfs/ordered-data.c
> @@ -1138,17 +1138,19 @@ static int clone_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pos,
>  					ordered->compress_type);
>  }
>  
> -int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
> -				u64 post)
> +/* split out a new ordered extent for this first @len bytes of @ordered */
> +int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 len)
>  {
>  	struct inode *inode = ordered->inode;
>  	struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
> -	struct rb_node *node;
>  	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> -	int ret = 0;
> +	struct rb_node *node;
>  
>  	trace_btrfs_ordered_extent_split(BTRFS_I(inode), ordered);
>  
> +	/* The bio must be entirely covered by the ordered extent */
> +	if (WARN_ON_ONCE(len > ordered->num_bytes))
> +		return -EINVAL;

Can we also reject "len == ordered->num_bytes" case here? So, we will never
modify the ordered extent to have
ordered->{num_bytes,disk_num_bytes,bytes_left} == 0.

Either way,

Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>

>  	/* We cannot split once end_bio'd ordered extent */
>  	if (WARN_ON_ONCE(ordered->bytes_left != ordered->disk_num_bytes))
>  		return -EINVAL;
> @@ -1167,11 +1169,11 @@ int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
>  	if (tree->last == node)
>  		tree->last = NULL;
>  
> -	ordered->file_offset += pre;
> -	ordered->disk_bytenr += pre;
> -	ordered->num_bytes -= (pre + post);
> -	ordered->disk_num_bytes -= (pre + post);
> -	ordered->bytes_left -= (pre + post);
> +	ordered->file_offset += len;
> +	ordered->disk_bytenr += len;
> +	ordered->num_bytes -= len;
> +	ordered->disk_num_bytes -= len;
> +	ordered->bytes_left -= len;
>  
>  	/* Re-insert the node */
>  	node = tree_insert(&tree->tree, ordered->file_offset, &ordered->rb_node);
> @@ -1182,13 +1184,7 @@ int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
>  
>  	spin_unlock_irq(&tree->lock);
>  
> -	if (pre)
> -		ret = clone_ordered_extent(ordered, 0, pre);
> -	if (ret == 0 && post)
> -		ret = clone_ordered_extent(ordered, pre + ordered->disk_num_bytes,
> -					   post);
> -
> -	return ret;
> +	return clone_ordered_extent(ordered, 0, len);
>  }
>  
>  int __init ordered_data_init(void)
> diff --git a/fs/btrfs/ordered-data.h b/fs/btrfs/ordered-data.h
> index 18007f9c00add8..f0f1138d23c331 100644
> --- a/fs/btrfs/ordered-data.h
> +++ b/fs/btrfs/ordered-data.h
> @@ -212,8 +212,7 @@ void btrfs_lock_and_flush_ordered_range(struct btrfs_inode *inode, u64 start,
>  					struct extent_state **cached_state);
>  bool btrfs_try_lock_ordered_range(struct btrfs_inode *inode, u64 start, u64 end,
>  				  struct extent_state **cached_state);
> -int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 pre,
> -			       u64 post);
> +int btrfs_split_ordered_extent(struct btrfs_ordered_extent *ordered, u64 len);
>  int __init ordered_data_init(void);
>  void __cold ordered_data_exit(void);
>  
> -- 
> 2.39.2
>