Re: [PATCH 03/14] xfs: dynamically allocate btree scrub context structure

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Sep 21, 2021 at 09:43:18AM +0100, Christoph Hellwig wrote:
> On Fri, Sep 17, 2021 at 06:29:26PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > Reorganize struct xchk_btree so that we can dynamically size the context
> > structure to fit the type of btree cursor that we have.  This will
> > enable us to use memory more efficiently once we start adding very tall
> > btree types.
> 
> So bs->levels[0].has_lastkey replaces bs->firstkey?  Can you explain
> a bit more how this works for someone not too familiar with the scrub
> code.

For each record and key that the btree scrubber encounters, it needs to
know if it should call ->{recs,keys}_inorder to check the ordering of
each item in the btree block.

Hmm.  Come to think of it, we could use "cur->bc_ptrs[level] > 0"
instead of tracking it separately.  Ok, that'll become a separate
cleanup patch to reduce memory further.  Good question!

> > +static inline size_t
> > +xchk_btree_sizeof(unsigned int levels)
> > +{
> > +	return sizeof(struct xchk_btree) +
> > +				(levels * sizeof(struct xchk_btree_levels));
> 
> This should probably use struct_size().

Assuming it's ok with sending a typed null pointer into a macro:

	return struct_size((struct xchk_btree *)NULL, levels, nr_levels);

Then ok.

--D