Re: [PATCH 2/3] xfs: go straight to real allocations for direct I/O COW writes

[Christoph Hellwig <hch@lst.de>]

On Wed, Dec 07, 2016 at 02:00:09PM -0500, Brian Foster wrote:
> > -	if (ap->flags & XFS_BMAPI_COWFORK)
> > -		align = xfs_get_cowextsz_hint(ap->ip);
> > -	else if (xfs_alloc_is_userdata(ap->datatype))
> > +	if (xfs_alloc_is_userdata(ap->datatype))
> 
> Doesn't this defeat the purpose (i.e., fragmentation avoidance via wider
> allocations) of the cowextszhint for direct I/O? I think it would be
> better to be consistent with the approach for traditional I/O + extsz
> and incorporate the alignment into the reservation. Perhaps the hunk of
> code that already does just that in xfs_iomap_write_direct() could be
> converted to a small helper and reused..?

We're already doing the alignment to the cowextsize hint in
__xfs_reflink_allocate_cow so that we can take the cowextsize into
account.

> > +	resblks = XFS_DIOSTRAT_SPACE_RES(mp, end_fsb - *offset_fsb);
> > +
> > +	error = xfs_qm_dqattach(ip, 0);
> 
> This is already in the (only) caller.

Yes, it can be dropped, although a superflous xfs_qm_dqattach is
totally harmless anyway.