Re: [PATCH 08/12] iomap: move folio_unlock out of iomap_writeback_folio

[Brian Foster <bfoster@redhat.com>]

On Fri, Jun 27, 2025 at 09:02:41AM +0200, Christoph Hellwig wrote:
> From: Joanne Koong <joannelkoong@gmail.com>
> 
> Move unlocking the folio out of iomap_writeback_folio into the caller.
> This means the end writeback machinery is now run with the folio locked
> when no writeback happend, or writeback completed extremely fast.
> 

I notice that folio_end_dropbehind_write() (via folio_end_writeback())
wants to trylock the folio in order to do its thing. Is this going to
cause issues with that (i.e. prevent invalidations)?

Brian

> This prepares for exporting iomap_writeback_folio for use in folio
> laundering.
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> [hch: split from a larger patch]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/buffered-io.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index c28eb6a6eee4..a1dccf4e7063 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1656,10 +1656,8 @@ static int iomap_writeback_folio(struct iomap_writeback_ctx *wpc,
>  
>  	trace_iomap_writeback_folio(inode, pos, folio_size(folio));
>  
> -	if (!iomap_writeback_handle_eof(folio, inode, &end_pos)) {
> -		folio_unlock(folio);
> +	if (!iomap_writeback_handle_eof(folio, inode, &end_pos))
>  		return 0;
> -	}
>  	WARN_ON_ONCE(end_pos <= pos);
>  
>  	if (i_blocks_per_folio(inode, folio) > 1) {
> @@ -1713,7 +1711,6 @@ static int iomap_writeback_folio(struct iomap_writeback_ctx *wpc,
>  	 * already at this point.  In that case we need to clear the writeback
>  	 * bit ourselves right after unlocking the page.
>  	 */
> -	folio_unlock(folio);
>  	if (ifs) {
>  		if (atomic_dec_and_test(&ifs->write_bytes_pending))
>  			folio_end_writeback(folio);
> @@ -1740,8 +1737,10 @@ iomap_writepages(struct iomap_writeback_ctx *wpc)
>  			PF_MEMALLOC))
>  		return -EIO;
>  
> -	while ((folio = writeback_iter(mapping, wpc->wbc, folio, &error)))
> +	while ((folio = writeback_iter(mapping, wpc->wbc, folio, &error))) {
>  		error = iomap_writeback_folio(wpc, folio);
> +		folio_unlock(folio);
> +	}
>  
>  	/*
>  	 * If @error is non-zero, it means that we have a situation where some
> -- 
> 2.47.2
> 
>