Re: [PATCH 3/5] xfs: restrict when we try to align cow fork delalloc to cowextsz hints

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

On Thu, Jun 13, 2024 at 07:06:13AM +0200, Christoph Hellwig wrote:
> On Wed, Jun 12, 2024 at 10:47:19AM -0700, Darrick J. Wong wrote:
> >  	xfs_filblks_t		prealloc,
> >  	struct xfs_bmbt_irec	*got,
> >  	struct xfs_iext_cursor	*icur,
> > -	int			eof)
> > +	int			eof,
> > +	bool			use_cowextszhint)
> 
> Looking at the caller below I don't think we need the use_cowextszhint
> flag here, we can just locally check for prealloc beeing non-0 in
> the branch below:

That won't work, because xfs_buffered_write_iomap_begin only sets
@prealloc to nonzero if it thinks is an extending write.  For the cow
fork, we create delalloc reservations that are aligned to the cowextsize
value for overwrites below eof.

--D

> > +	/*
> > +	 * If the caller wants us to do so, try to expand the range of the
> > +	 * delalloc reservation up and down so that it's aligned with the CoW
> > +	 * extent size hint.  Unlike the data fork, the CoW cancellation
> > +	 * functions will free all the reservations at inactivation, so we
> > +	 * don't require that every delalloc reservation have a dirty
> > +	 * pagecache.
> > +	 */
> > +	if (whichfork == XFS_COW_FORK && use_cowextszhint) {
> 
> Which keeps all the logic and the comments in one single place.
> 
>