Re: [PATCH v4 12/13] ext4: move pagecache_isize_extended() out of active handle

[Jan Kara]

On Fri 27-03-26 18:29:38, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> In ext4_alloc_file_blocks(), pagecache_isize_extended() is called under
> an active handle and may also hold folio lock if the block size is
> smaller than the folio size. This also breaks the "folio lock ->
> transaction start" lock ordering for the upcoming iomap buffered I/O
> path.
> 
> Therefore, move pagecache_isize_extended() outside of an active handle.
> Additionally, it is unnecessary to update the file length during each
> iteration of the allocation loop. Instead, update the file length only
> to the position where the allocation is successful. Postpone updating
> the inode size until after the allocation loop completes or is
> interrupted due to an error.
> 
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

Looks good! Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/ext4/extents.c | 62 +++++++++++++++++++++++++++++------------------
>  1 file changed, 39 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 7abe47f923c0..f13f604b1f67 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4553,7 +4553,7 @@ static int ext4_alloc_file_blocks(struct file *file, loff_t offset, loff_t len,
>  	ext4_lblk_t len_lblk;
>  	struct ext4_map_blocks map;
>  	unsigned int credits;
> -	loff_t epos, old_size = i_size_read(inode);
> +	loff_t epos = 0, old_size = i_size_read(inode);
>  	unsigned int blkbits = inode->i_blkbits;
>  	bool alloc_zero = false;
>  
> @@ -4618,44 +4618,60 @@ static int ext4_alloc_file_blocks(struct file *file, loff_t offset, loff_t len,
>  			ext4_journal_stop(handle);
>  			break;
>  		}
> +		ext4_update_inode_fsync_trans(handle, inode, 1);
> +		ret = ext4_journal_stop(handle);
> +		if (unlikely(ret))
> +			break;
> +
>  		/*
>  		 * allow a full retry cycle for any remaining allocations
>  		 */
>  		retries = 0;
> -		epos = EXT4_LBLK_TO_B(inode, map.m_lblk + ret);
> -		if (new_size) {
> -			if (epos > new_size)
> -				epos = new_size;
> -			ext4_update_inode_size(inode, epos);
> -			if (epos > old_size)
> -				pagecache_isize_extended(inode, old_size, epos);
> -		}
> -		ret2 = ext4_mark_inode_dirty(handle, inode);
> -		ext4_update_inode_fsync_trans(handle, inode, 1);
> -		ret3 = ext4_journal_stop(handle);
> -		ret2 = ret3 ? ret3 : ret2;
> -		if (unlikely(ret2))
> -			break;
>  
>  		if (alloc_zero &&
>  		    (map.m_flags & (EXT4_MAP_MAPPED | EXT4_MAP_UNWRITTEN))) {
> -			ret2 = ext4_issue_zeroout(inode, map.m_lblk, map.m_pblk,
> -						  map.m_len);
> -			if (likely(!ret2))
> -				ret2 = ext4_convert_unwritten_extents(NULL,
> +			ret = ext4_issue_zeroout(inode, map.m_lblk, map.m_pblk,
> +						 map.m_len);
> +			if (likely(!ret))
> +				ret = ext4_convert_unwritten_extents(NULL,
>  					inode, (loff_t)map.m_lblk << blkbits,
>  					(loff_t)map.m_len << blkbits);
> -			if (ret2)
> +			if (ret)
>  				break;
>  		}
>  
> -		map.m_lblk += ret;
> -		map.m_len = len_lblk = len_lblk - ret;
> +		map.m_lblk += map.m_len;
> +		map.m_len = len_lblk = len_lblk - map.m_len;
> +		epos = EXT4_LBLK_TO_B(inode, map.m_lblk);
>  	}
> +
>  	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
>  		goto retry;
>  
> -	return ret > 0 ? ret2 : ret;
> +	if (!epos || !new_size)
> +		return ret;
> +
> +	/*
> +	 * Allocate blocks, update the file size to match the size of the
> +	 * already successfully allocated blocks.
> +	 */
> +	if (epos > new_size)
> +		epos = new_size;
> +
> +	handle = ext4_journal_start(inode, EXT4_HT_MISC, 1);
> +	if (IS_ERR(handle))
> +		return ret ? ret : PTR_ERR(handle);
> +
> +	ext4_update_inode_size(inode, epos);
> +	ret2 = ext4_mark_inode_dirty(handle, inode);
> +	ext4_update_inode_fsync_trans(handle, inode, 1);
> +	ret3 = ext4_journal_stop(handle);
> +	ret2 = ret3 ? ret3 : ret2;
> +
> +	if (epos > old_size)
> +		pagecache_isize_extended(inode, old_size, epos);
> +
> +	return ret ? ret : ret2;
>  }
>  
>  static int ext4_collapse_range(struct file *file, loff_t offset, loff_t len);
> -- 
> 2.52.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR