Re: [PATCH v2 08/13] xfs: Do not free EOF blocks for forcealign

Dave Chinner
2024-07-08T01:45:03Z

On Sat, Jul 06, 2024 at 09:56:09AM +0200, Christoph Hellwig wrote:
> On Fri, Jul 05, 2024 at 04:24:45PM +0000, John Garry wrote:
> > - if (xfs_inode_has_bigrtalloc(ip))
> > +
> > + /* Only try to free beyond the allocation unit that crosses EOF */
> > + if (xfs_inode_has_forcealign(ip))
> > + end_fsb = roundup_64(end_fsb, ip->i_extsize);
> > + else if (xfs_inode_has_bigrtalloc(ip))
> > end_fsb = xfs_rtb_roundup_rtx(mp, end_fsb);
>
> Shouldn't we have a common helper to align things the right way?

Yes, that's what I keep saying. The common way to do this is:

align = xfs_inode_alloc_unitsize(ip);
if (align > mp->m_blocksize)
end_fsb = roundup_64(end_fsb, align);

Wrapping that into a helper might be appropriate, though we'd need
wrappers for aligning both the start (down) and end (up).

To make this work, the xfs_inode_alloc_unitsize() code needs to grow
a forcealign check. That overrides the RT rextsize value (force
align on RT should work the same as it does on data devs) and needs
to look like this:

unsigned int blocks = 1;

+ if (xfs_inode_has_forcealign(ip)
+ blocks = ip->i_extsize;
- if (XFS_IS_REALTIME_INODE(ip))
+ else if (XFS_IS_REALTIME_INODE(ip))
blocks = ip->i_mount->m_sb.sb_rextsize;

return XFS_FSB_TO_B(ip->i_mount, blocks);

> But more importantly shouldn't this also cover hole punching if we
> really want force aligned boundaries?

Yes, that's what I keep saying. There is no difference in the
alignment behaviour needed for "xfs_inode_has_bigrtalloc" and
"xfs_inode_has_forcealign" except for the source of the allocation
alignment value.

-Dave.
--
Dave Chinner
david@fromorbit.com