Re: [PATCH v3 10/21] xfs: Update xfs_is_falloc_aligned() mask for forcealign

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

On Wed, May 01, 2024 at 11:48:59AM +0100, John Garry wrote:
> On 01/05/2024 00:35, Dave Chinner wrote:
> > >   	return !((pos | len) & mask);
> > I think this whole function needs to be rewritten so that
> > non-power-of-2 extent sizes are supported on both devices properly.
> > 
> > 	xfs_extlen_t	fsbs = 1;
> > 	u64		bytes;
> > 	u32		mod;
> > 
> > 	if (xfs_inode_has_forcealign(ip))
> > 		fsbs = ip->i_extsize;
> > 	else if (XFS_IS_REALTIME_INODE(ip))
> > 		fsbs = mp->m_sb.sb_rextsize;
> > 
> > 	bytes = XFS_FSB_TO_B(mp, fsbs);
> > 	if (is_power_of_2(fsbs))
> > 		return !((pos | len) & (bytes - 1));
> > 
> > 	div_u64_rem(pos, bytes, &mod);
> > 	if (mod)
> > 		return false;
> > 	div_u64_rem(len, bytes, &mod);
> > 	return mod == 0;
> 
> ok, but I still have a doubt about non-power-of-2 forcealign extsize
> support.

The trouble is, non-power-of-2 extent size hints are supported for
regular and realtime files for funny cases like trying to align
allocations to RAID stripes.  I think it would be hard to drop support
for this, given that means that old filesystems can't ever get upgraded
to forcealign.

--D

> Thanks,
> John
>