Re: [PATCH v2 06/14] fs: xfs: Do not free EOF blocks for forcealign

[John Garry]

> >   	 */
> >   	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)XFS_ISIZE(ip));
> > -	if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
> > +
> > +	/* Do not free blocks when forcing extent sizes */
>
> That comment seems wrong - this just rounds up where we start
> trimming from to be aligned...

ok

> > +	if (xfs_get_extsz(ip) > 1)
> > +		end_fsb = roundup_64(end_fsb, xfs_get_extsz(ip));
> > +	else if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
> >   		end_fsb = xfs_rtb_roundup_rtx(mp, end_fsb);
>
> I think this would be better written as:
>
> 	/*
> 	 * Forced extent alignment requires us to round up where we
> 	 * start trimming from so that result is correctly aligned.
> 	 */
> 	if (xfs_inode_forcealign(ip)) {
> 		if (ip->i_extsize > 1)
> 			end_fsb = roundup_64(end_fsb, ip->i_extsize);
> 		else if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
> 			end_fsb = xfs_rtb_roundup_rtx(mp, end_fsb);
> 	}
>
> Because we only want end-fsb alignment when forced alignment is
> required.

But why change current rtvol behaviour?

> Which then makes me wonder: truncate needs this, too, doesn't it?
> And the various fallocate() ops like hole punching and extent
> shifting?

Yes, I would think so. I quickly checked rtvol for truncate and it does 
the round up. I would need to check the relevant code for truncate and 
fallocate for forcealign now.

I do also wonder if we could factor out this rounding up code for 
truncate, facallocate, and whatever else.

> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index 2c439df8c47f..bbb8886f1d32 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -65,6 +65,20 @@ xfs_get_extsz_hint(
> >   	return 0;
> >   }
> >   
> > +/*
> > + * Helper function to extract extent size. It will return a power-of-2,
> > + * as forcealign requires this.
> > + */
> > +xfs_extlen_t
> > +xfs_get_extsz(
> > +	struct xfs_inode	*ip)
> > +{
> > +	if (xfs_inode_forcealign(ip) && ip->i_extsize)
> > +		return ip->i_extsize;
> > +
> > +	return 1;
> > +}
>
> This can go away - if it is needed elsewhere, then I think it would
> be better open coded because it better documents what the code is
> doing...

I would rather get rid of xfs_get_extsz() for sure.

Thanks,
John