linux-kernel - Re: [PATCH v2 05/13] ext4: correct the mapping status if the extent has been zeroed

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Message-ID: <aSbq-cXrYMdA74jm@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Wed, 26 Nov 2025 17:26:41 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
        jack@...e.cz, yi.zhang@...wei.com, yizhang089@...il.com,
        libaokun1@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v2 05/13] ext4: correct the mapping status if the extent
 has been zeroed

On Fri, Nov 21, 2025 at 02:08:03PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> Before submitting I/O and allocating blocks with the
> EXT4_GET_BLOCKS_PRE_IO flag set, ext4_split_convert_extents() may
> convert the target extent range to initialized due to ENOSPC, ENOMEM, or
> EQUOTA errors. However, it still marks the mapping as incorrectly
> unwritten. Although this may not seem to cause any practical problems,
> it will result in an unnecessary extent conversion operation after I/O
> completion. Therefore, it's better to correct the returned mapping
> status.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Looks good, feel free to add:
Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>

Regards,
ojaswin

> ---
>  fs/ext4/extents.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 2db84f6b0056..19338f488550 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3916,6 +3916,8 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
>  
>  	/* get_block() before submitting IO, split the extent */
>  	if (flags & EXT4_GET_BLOCKS_PRE_IO) {
> +		int depth;
> +
>  		path = ext4_split_convert_extents(handle, inode, map, path,
>  						  flags, allocated);
>  		if (IS_ERR(path))
> @@ -3931,7 +3933,13 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
>  			err = -EFSCORRUPTED;
>  			goto errout;
>  		}
> -		map->m_flags |= EXT4_MAP_UNWRITTEN;
> +		/* Don't mark unwritten if the extent has been zeroed out. */
> +		path = ext4_find_extent(inode, map->m_lblk, path, flags);
> +		if (IS_ERR(path))
> +			return path;
> +		depth = ext_depth(inode);
> +		if (ext4_ext_is_unwritten(path[depth].p_ext))
> +			map->m_flags |= EXT4_MAP_UNWRITTEN;
>  		goto out;
>  	}
>  	/* IO end_io complete, convert the filled extent to written */
> -- 
> 2.46.1
>