Re: [PATCH] xfs_repair: estimate per-AG btree slack better

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

On Tue, May 02, 2023 at 12:49:44PM +0200, Carlos Maiolino wrote:
> Hi.
> 
> On Thu, Apr 27, 2023 at 03:45:21PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > The slack calculation for per-AG btrees is a bit inaccurate because it
> > only disables slack space in the new btrees when the amount of free
> > space in the AG (not counting the btrees) is less than 3/32ths of the
> > AG.  In other words, it assumes that the btrees will fit in less than 9
> > percent of the space.
> .
> .
> .
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> 
> This looks fine, with a small caveat below...
> 
> .
> .
> .
> 
> > +
> > +static xfs_extlen_t
> > +estimate_allocbt_blocks(
> > +	struct xfs_perag	*pag,
> > +	unsigned int		nr_extents)
> > +{
> > +	return libxfs_allocbt_calc_size(pag->pag_mount, nr_extents) * 2;
> > +}
> 
> Forgive my ignorance here, but what's the reason of the magic number? It seems
> to me by multiplying by 2 here, you are considering a split of every single
> leaf for the calculated btree size, but I'm not sure if that's the intention,
> could you please confirm or correct me? :)

Ah, I should document that better...

	/* Account for space consumed by both free space btrees */
	return libxfs_allocbt_calc_size(...) * 2;

--D

> Other than that, the patch looks good
> 
> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
> 
> -- 
> Carlos Maiolino