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

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On 08/07/2024 02:44, Dave Chinner wrote:
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.

Such a change was introduced in https://lore.kernel.org/linux-xfs/20240501235310.GP360919@frogsfrogsfrogs/

and, as you can see, Darrick was less than happy with it. That is why I kept this method which removed recently added RT code.

Darrick, can we find a better method to factor this code out, like below?

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;

That's in 09/13


         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?

so doesn't the xfs_file_fallocate(PUNCH_HOLES) -> xfs_flush_unmap_range() -> rounding with xfs_inode_alloc_unitsize() do the required job?


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.








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