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

Brian Foster
2016-08-02T18:48:49Z

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@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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