Re: [PATCH 13/19] xfs: vectorise directory data operations

Ben Myers
2013-10-24T22:28:14Z

On Fri, Oct 25, 2013 at 09:08:44AM +1100, Dave Chinner wrote:
> On Thu, Oct 24, 2013 at 04:41:12PM -0500, Ben Myers wrote:
> > On Fri, Oct 25, 2013 at 08:31:17AM +1100, Dave Chinner wrote:
> > > On Thu, Oct 24, 2013 at 01:39:09PM -0500, Ben Myers wrote:
> > > > On Tue, Oct 15, 2013 at 09:17:59AM +1100, Dave Chinner wrote:
> > > > > From: Dave Chinner <dchinner@redhat.com>
> > > > >
> > > > > Following from the initial patches to vectorise the shortform
> > > > > directory encode/decode operations, convert half the data block
> > > > > operations to use the vector. The rest will be done in a second
> > > > > patch.
> > > > >
> > > > > This further reduces the size of the built binary:
> > > > >
> > > > > text data bss dec hex filename
> > > > > 794490 96802 1096 892388 d9de4 fs/xfs/xfs.o.orig
> > > > > 792986 96802 1096 890884 d9804 fs/xfs/xfs.o.p1
> > > > > 792350 96802 1096 890248 d9588 fs/xfs/xfs.o.p2
> > > > > 789293 96802 1096 887191 d8997 fs/xfs/xfs.o.p3
> > > > >
> > > > > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > > > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > >
> > > > Generally looks pretty good, I have a question below...
> > > >
> > > > > const struct xfs_dir_ops xfs_dir2_ftype_ops = {
> > > > > @@ -223,6 +415,18 @@ const struct xfs_dir_ops xfs_dir2_ftype_ops = {
> > > > > .sf_put_ino = xfs_dir3_sfe_put_ino,
> > > > > .sf_get_parent_ino = xfs_dir2_sf_get_parent_ino,
> > > > > .sf_put_parent_ino = xfs_dir2_sf_put_parent_ino,
> > > > > +
> > > > > + .data_entsize = xfs_dir3_data_entsize,
> > > > > + .data_get_ftype = xfs_dir3_data_get_ftype,
> > > > > + .data_put_ftype = xfs_dir3_data_put_ftype,
> > > > > + .data_entry_tag_p = xfs_dir3_data_entry_tag_p,
> > > > > +
> > > > > + .data_dot_offset = xfs_dir2_data_dot_offset,
> > > > > + .data_dotdot_offset = xfs_dir2_data_dotdot_offset,
> > > > > + .data_first_offset = xfs_dir2_data_first_offset,
> > > > > + .data_dot_entry_p = xfs_dir2_data_dot_entry_p,
> > > > > + .data_dotdot_entry_p = xfs_dir2_data_dotdot_entry_p,
> > > > > + .data_first_entry_p = xfs_dir2_data_first_entry_p,
> > > > > };
> > > >
> > > > I think there may be a problem here. Although the dirv2 functions for
> > > > ., .., and first entry offset account for the v2 header size, they
> > > > appear not to be accounting for the modified entry size due to the file
> > > > type field. Am I missing something?
> > >
> > > The ftype field is handled by the alignment roundup. i.e. namelen is
> > > 1 or two bytes, plus ftype is 2 or 3 bytes, roundup is to 8 bytes.
> > > Hence adding a byte for the ftype field is not a problem for these
> > > first entries because of their small, fixed size.
>
> I should point out that this code is functionally identical to the
> way the original macros treated the v4 ftype code. You reviewed that
> code and tested it and it as such this implicit use of padding was
> considered perfectly OK just a couple of months ago.....

It is a detail that I overlooked. I try to do a thorough review... but
sometimes things don't register.

> > It should either be explicitly correct (and I think it is today), or we
> > need a comment to explain why it's not. I would prefer the former.
>
> Well, I'll add a patch at the end of the series to change it. I don't want to
> have to rebase the rest of the patches in the series just because of the
> don't apply because of context mismatches.

Sounds great.

>
> Besides, the last patch in the series it replaces the offset functions with
> precalculated values. That replacement fixes the offset calculation to
> explicitly use dir2 hdrs and dir3 entsizes, so the problem goes away for
> those entries.

Ok, I'll look out for it then.

Thanks,
Ben