Re: [PATCH v6 07/31] ext4: allow ext4_map_blocks() to start its own transaction handle

[Ojaswin Mujoo]

On Thu, Sep 03, 2026 at 08:35:19PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> Make ext4_map_blocks() start its own transaction handle when the caller
> does not provide one. The handle is started after the lookup path
> confirms that allocation is actually needed, and is stopped at the
> unified out_handle exit path. This avoids unnecessarily starting a
> handle for pure mapping queries. This prepares for the buffered iomap
> writeback conversion, which improves performance for fragile overwrite
> cases.
> 
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

Looks good Zhang,

Reviewed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>

Regards,
ojaswin

> ---
>  fs/ext4/inode.c | 36 +++++++++++++++++++++++++++---------
>  1 file changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 73af6d386985..c9dea4ca5caf 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -703,6 +703,7 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
>  	struct extent_status es;
>  	int retval;
>  	int ret = 0;
> +	bool internal_handle = false;
>  	unsigned int orig_mlen;
>  #ifdef ES_AGGRESSIVE_TEST
>  	struct ext4_map_blocks orig_map;
> @@ -787,13 +788,15 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
>  	retval = ext4_map_query_blocks(handle, inode, map, flags);
>  	up_read((&EXT4_I(inode)->i_data_sem));
>  	if (retval < 0)
> -		return retval;
> +		goto out_handle;
>  
>  found:
>  	if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
>  		ret = check_block_validity(inode, map);
> -		if (ret != 0)
> -			return ret;
> +		if (ret != 0) {
> +			retval = ret;
> +			goto out_handle;
> +		}
>  	}
>  
>  	/* If it is only a block(s) look up */
> @@ -813,8 +816,15 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
>  		 * ext4_ext_map_blocks()
>  		 */
>  		if (!(flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN))
> -			return retval;
> +			goto out_handle;
>  
> +	if (!handle) {
> +		handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS,
> +				ext4_chunk_trans_blocks(inode, orig_mlen));
> +		if (IS_ERR(handle))
> +			return PTR_ERR(handle);
> +		internal_handle = true;
> +	}
>  
>  	ext4_fc_track_inode(handle, inode);
>  	/*
> @@ -843,12 +853,14 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
>  	if (retval < 0)
>  		ext_debug(inode, "failed with err %d\n", retval);
>  	if (retval <= 0)
> -		return retval;
> +		goto out_handle;
>  
>  	if (map->m_flags & EXT4_MAP_MAPPED) {
>  		ret = check_block_validity(inode, map);
> -		if (ret != 0)
> -			return ret;
> +		if (ret != 0) {
> +			retval = ret;
> +			goto out_handle;
> +		}
>  
>  		/*
>  		 * Inodes with freshly allocated blocks where contents will be
> @@ -869,12 +881,18 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
>  			else
>  				ret = ext4_jbd2_inode_add_write(handle, inode,
>  						start_byte, length);
> -			if (ret)
> -				return ret;
> +			if (ret) {
> +				retval = ret;
> +				goto out_handle;
> +			}
>  		}
>  	}
>  	ext4_fc_track_range(handle, inode, map->m_lblk, map->m_lblk +
>  			    map->m_len - 1);
> +
> +out_handle:
> +	if (internal_handle)
> +		ext4_journal_stop(handle);
>  	return retval;
>  }
>  
> -- 
> 2.52.0
>