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

[Brian Foster <bfoster@redhat.com>]

On Wed, Dec 07, 2016 at 08:37:09PM +0100, Christoph Hellwig wrote:
> 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.
> 

Only for end_fsb... xfs_bmap_btalloc() calls xfs_bmap_extsize_align()
with the alignment, which rounds out the start and end offsets.

This same end_fsb code has already been removed from
xfs_reflink_reserve_cow() for similar reasons. It should probably be
removed from xfs_reflink_allocate_cow() as well.

Brian

> > > +	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.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html