Re: [PATCH 1/3] xfs: refactor agfl length computation function

[Brian Foster <bfoster@redhat.com>]

On Wed, Dec 18, 2019 at 11:37:28AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Refactor xfs_alloc_min_freelist to accept a NULL @pag argument, in which
> case it returns the largest possible minimum length.  This will be used
> in an upcoming patch to compute the length of the AGFL at mkfs time.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/libxfs/xfs_alloc.c |   18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index c284e10af491..fc93fd88ec89 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2248,24 +2248,32 @@ xfs_alloc_longest_free_extent(
>  	return pag->pagf_flcount > 0 || pag->pagf_longest > 0;
>  }
>  
> +/*
> + * Compute the minimum length of the AGFL in the given AG.  If @pag is NULL,
> + * return the largest possible minimum length.
> + */
>  unsigned int
>  xfs_alloc_min_freelist(
>  	struct xfs_mount	*mp,
>  	struct xfs_perag	*pag)
>  {
> +	/* AG btrees have at least 1 level. */
> +	static const uint8_t	fake_levels[XFS_BTNUM_AGF] = {1, 1, 1};
> +	const uint8_t		*levels = pag ? pag->pagf_levels : fake_levels;
>  	unsigned int		min_free;
>  
> +	ASSERT(mp->m_ag_maxlevels > 0);
> +
>  	/* space needed by-bno freespace btree */
> -	min_free = min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_BNOi] + 1,
> +	min_free = min_t(unsigned int, levels[XFS_BTNUM_BNOi] + 1,
>  				       mp->m_ag_maxlevels);
>  	/* space needed by-size freespace btree */
> -	min_free += min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_CNTi] + 1,
> +	min_free += min_t(unsigned int, levels[XFS_BTNUM_CNTi] + 1,
>  				       mp->m_ag_maxlevels);
>  	/* space needed reverse mapping used space btree */
>  	if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> -		min_free += min_t(unsigned int,
> -				  pag->pagf_levels[XFS_BTNUM_RMAPi] + 1,
> -				  mp->m_rmap_maxlevels);
> +		min_free += min_t(unsigned int, levels[XFS_BTNUM_RMAPi] + 1,
> +						mp->m_rmap_maxlevels);
>  
>  	return min_free;
>  }
>