Re: [PATCH v2 3/7] iomap: Remove unnecessary test from iomap_release_folio()

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

On Fri, Jun 02, 2023 at 11:24:40PM +0100, Matthew Wilcox (Oracle) wrote:
> The check for the folio being under writeback is unnecessary; the caller
> has checked this and the folio is locked, so the folio cannot be under
> writeback at this point.

Do we need a debug assertion here to validate that filemap_release_folio
has already filtered out folios unergoing writeback?  The documentation
change in the next patch might be fine since you're the pagecache
maintainer.

> The comment is somewhat misleading in that it talks about one specific
> situation in which we can see a dirty folio.  There are others, so change
> the comment to explain why we can't release the iomap_page.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  fs/iomap/buffered-io.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 08ee293c4117..2054b85c9d9b 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -483,12 +483,10 @@ bool iomap_release_folio(struct folio *folio, gfp_t gfp_flags)
>  			folio_size(folio));
>  
>  	/*
> -	 * mm accommodates an old ext3 case where clean folios might
> -	 * not have had the dirty bit cleared.  Thus, it can send actual
> -	 * dirty folios to ->release_folio() via shrink_active_list();
> -	 * skip those here.
> +	 * If the folio is dirty, we refuse to release our metadata because
> +	 * it may be partially dirty (FIXME, add a test for that).

Er... is this FIXME reflective of incomplete code?

--D

>  	 */
> -	if (folio_test_dirty(folio) || folio_test_writeback(folio))
> +	if (folio_test_dirty(folio))
>  		return false;
>  	iomap_page_release(folio);
>  	return true;
> -- 
> 2.39.2
>