Re: [PATCH v3 7/8] xfs: replace zero range flush with folio batch

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Mar 09, 2026 at 09:45:05AM -0400, Brian Foster wrote:
> Now that the zero range pagecache flush is purely isolated to
> providing zeroing correctness in this case, we can remove it and
> replace it with the folio batch mechanism that is used for handling
> unwritten extents.
> 
> This is still slightly odd in that XFS reports a hole vs. a mapping
> that reflects the COW fork extents, but that has always been the
> case in this situation and so a separate issue. We drop the iomap
> warning that assumes the folio batch is always associated with
> unwritten mappings, but this is mainly a development assertion as
> otherwise the core iomap fbatch code doesn't care much about the
> mapping type if it's handed the set of folios to process.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

This is (in the end) a much cleaner solution :)
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/iomap/buffered-io.c |  4 ----
>  fs/xfs/xfs_iomap.c     | 20 ++++++--------------
>  2 files changed, 6 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 0999aca6e5cc..4422a6d477d7 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1633,10 +1633,6 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
>  	while ((ret = iomap_iter(&iter, ops)) > 0) {
>  		const struct iomap *srcmap = iomap_iter_srcmap(&iter);
>  
> -		if (WARN_ON_ONCE((iter.iomap.flags & IOMAP_F_FOLIO_BATCH) &&
> -				 srcmap->type != IOMAP_UNWRITTEN))
> -			return -EIO;
> -
>  		if (!(iter.iomap.flags & IOMAP_F_FOLIO_BATCH) &&
>  		    (srcmap->type == IOMAP_HOLE ||
>  		     srcmap->type == IOMAP_UNWRITTEN)) {
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index ce342b9ce2f0..df240931f07a 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1781,7 +1781,6 @@ xfs_buffered_write_iomap_begin(
>  {
>  	struct iomap_iter	*iter = container_of(iomap, struct iomap_iter,
>  						     iomap);
> -	struct address_space	*mapping = inode->i_mapping;
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	struct xfs_mount	*mp = ip->i_mount;
>  	xfs_fileoff_t		offset_fsb = XFS_B_TO_FSBT(mp, offset);
> @@ -1813,7 +1812,6 @@ xfs_buffered_write_iomap_begin(
>  	if (error)
>  		return error;
>  
> -restart:
>  	error = xfs_ilock_for_iomap(ip, flags, &lockmode);
>  	if (error)
>  		return error;
> @@ -1866,8 +1864,8 @@ xfs_buffered_write_iomap_begin(
>  
>  	/*
>  	 * We may need to zero over a hole in the data fork if it's fronted by
> -	 * COW blocks and dirty pagecache. To make sure zeroing occurs, force
> -	 * writeback to remap pending blocks and restart the lookup.
> +	 * COW blocks and dirty pagecache. Scan such file ranges for dirty
> +	 * cache and fill the iomap batch with folios that need zeroing.
>  	 */
>  	if ((flags & IOMAP_ZERO) && imap.br_startoff > offset_fsb) {
>  		loff_t	start, end;
> @@ -1889,16 +1887,10 @@ xfs_buffered_write_iomap_begin(
>  		xfs_trim_extent(&imap, offset_fsb,
>  			    cmap.br_startoff + cmap.br_blockcount - offset_fsb);
>  		start = XFS_FSB_TO_B(mp, imap.br_startoff);
> -		end = XFS_FSB_TO_B(mp,
> -				   imap.br_startoff + imap.br_blockcount) - 1;
> -		if (filemap_range_needs_writeback(mapping, start, end)) {
> -			xfs_iunlock(ip, lockmode);
> -			error = filemap_write_and_wait_range(mapping, start,
> -							     end);
> -			if (error)
> -				return error;
> -			goto restart;
> -		}
> +		end = XFS_FSB_TO_B(mp, imap.br_startoff + imap.br_blockcount);
> +		iomap_fill_dirty_folios(iter, &start, end, &iomap_flags);
> +		xfs_trim_extent(&imap, offset_fsb,
> +				XFS_B_TO_FSB(mp, start) - offset_fsb);
>  
>  		goto found_imap;
>  	}
> -- 
> 2.52.0
> 
>