Re: [PATCH 010/119] xfs: create a standard btree size calculator code

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On Thu, Jun 16, 2016 at 06:18:56PM -0700, Darrick J. Wong wrote:
> Create a helper to generate AG btree height calculator functions.
> This will be used (much) later when we get to the refcount btree.
> 
> v2: Use a helper function instead of a macro.
> v3: We can (theoretically) store more than 2^32 records in a btree, so
>     widen the fields to accept that.
> v4: Don't modify xfs_bmap_worst_indlen; the purpose of /that/ function
>     is to estimate the worst-case number of blocks needed for a bmbt
>     expansion, not to calculate the space required to store nr records.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---

I think this one should probably be pushed out to where it is used
(easier to review with an example imo). I don't see it used anywhere up
through the rmapbt stuff, anyways...

>  fs/xfs/libxfs/xfs_btree.c |   27 +++++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_btree.h |    3 +++
>  2 files changed, 30 insertions(+)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> index 105979d..5eb4e40 100644
> --- a/fs/xfs/libxfs/xfs_btree.c
> +++ b/fs/xfs/libxfs/xfs_btree.c
> @@ -4156,3 +4156,30 @@ xfs_btree_sblock_verify(
>  
>  	return true;
>  }
> +
> +/*
> + * Calculate the number of blocks needed to store a given number of records
> + * in a short-format (per-AG metadata) btree.
> + */
> +xfs_extlen_t
> +xfs_btree_calc_size(
> +	struct xfs_mount	*mp,
> +	uint			*limits,
> +	unsigned long long	len)
> +{
> +	int			level;
> +	int			maxrecs;
> +	xfs_extlen_t		rval;
> +
> +	maxrecs = limits[0];
> +	for (level = 0, rval = 0; len > 0; level++) {

len is unsigned, so len > 0 is kind of pointless. Perhaps check len > 1
and kill the check in the loop?

Brian

> +		len += maxrecs - 1;
> +		do_div(len, maxrecs);
> +		rval += len;
> +		if (len == 1)
> +			return rval;
> +		if (level == 0)
> +			maxrecs = limits[1];
> +	}
> +	return rval;
> +}
> diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
> index 9a88839..b330f19 100644
> --- a/fs/xfs/libxfs/xfs_btree.h
> +++ b/fs/xfs/libxfs/xfs_btree.h
> @@ -475,4 +475,7 @@ static inline int xfs_btree_get_level(struct xfs_btree_block *block)
>  bool xfs_btree_sblock_v5hdr_verify(struct xfs_buf *bp);
>  bool xfs_btree_sblock_verify(struct xfs_buf *bp, unsigned int max_recs);
>  
> +xfs_extlen_t xfs_btree_calc_size(struct xfs_mount *mp, uint *limits,
> +		unsigned long long len);
> +
>  #endif	/* __XFS_BTREE_H__ */
> 
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