[PATCH 20/47] xfs: increase XFS_BTREE_MAXLEVELS to fit the rmapbt

[Brian Foster]

On Wed, Jul 20, 2016 at 09:58:17PM -0700, Darrick J. Wong wrote:
> By my calculations, a 1,073,741,824 block AG with a 1k block size
> can attain a maximum height of 9.  Assuming a record size of 24
> bytes, a key/ptr size of 44 bytes, and half-full btree nodes,
> we'd need 53,687,092 blocks for the records and ~6 million blocks
> for the keys.  That requires a btree of height 9.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
> ---

I believe you.. :) but could you add a bit more detail to the commit log
just to describe the calculations (e.g., how many records per leaf
block, keys per node block) so 1.) I don't have to try and figure it out
;) (and probably get it wrong) and 2.) so we have a reference in the git
repo going forward?

Brian

>  fs/xfs/libxfs/xfs_btree.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
> index b8bbb21..629ef4f 100644
> --- a/fs/xfs/libxfs/xfs_btree.h
> +++ b/fs/xfs/libxfs/xfs_btree.h
> @@ -133,7 +133,7 @@ do {    \
>  	}       \
>  } while (0)
>  
> -#define	XFS_BTREE_MAXLEVELS	8	/* max of all btrees */
> +#define	XFS_BTREE_MAXLEVELS	9	/* max of all btrees */
>  
>  struct xfs_btree_ops {
>  	/* size of the key and record structures */
> 
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