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

Brian Foster
2016-06-20T14:31:56Z

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@oracle.com>
> ---

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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