Re: [PATCH v2 2/3] xfs: support additional levels in the agfl minimum calculation

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Aug 14, 2026 at 09:22:38AM -0400, Brian Foster wrote:
> xfs_alloc_min_freelist() calculates the worst case AGFL block
> requirement for a full split plus partial refill for each alloc
> btree. An upcoming patch needs to calculate the requirement for
> multiple level increases, so add an optional extra levels parameter
> and factor out a wrapper function for the common case of a single
> split. No functional changes.
> 
> Assisted-by: LLM
> Signed-off-by: Brian Foster <bfoster@redhat.com>

This looks like a simple enough hoist, so I'll move on to the next patch
to see how it's used.  In the meantime,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/xfs/libxfs/xfs_alloc.c | 31 +++++++++++++++++++++++--------
>  1 file changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index d99602bcc16f..dbb85fb6314b 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2439,17 +2439,22 @@ xfs_alloc_longest_free_extent(
>  
>  /*
>   * Compute the minimum length of the AGFL in the given AG.  If @pag is NULL,
> - * return the largest possible minimum length.
> + * return the largest possible minimum length. The base calculation accounts
> + * for a single full split per btree. @extra_levels adds additional split
> + * levels to compute the prospective AGFL requirement increase for
> + * multi-allocation transactions.
>   */
> -unsigned int
> -xfs_alloc_min_freelist(
> +static unsigned int
> +__xfs_alloc_min_freelist(
>  	struct xfs_mount	*mp,
> -	struct xfs_perag	*pag)
> +	struct xfs_perag	*pag,
> +	unsigned int		extra_levels)
>  {
>  	/* AG btrees have at least 1 level. */
>  	const unsigned int	bno_level = pag ? pag->pagf_bno_level : 1;
>  	const unsigned int	cnt_level = pag ? pag->pagf_cnt_level : 1;
>  	const unsigned int	rmap_level = pag ? pag->pagf_rmap_level : 1;
> +	const unsigned int	levels = 1 + extra_levels;
>  	unsigned int		min_free;
>  
>  	ASSERT(mp->m_alloc_maxlevels > 0);
> @@ -2476,15 +2481,25 @@ xfs_alloc_min_freelist(
>  	 */
>  
>  	/* space needed by-bno freespace btree */
> -	min_free = min(bno_level + 1, mp->m_alloc_maxlevels) * 2 - 2;
> +	min_free = min(bno_level + levels, mp->m_alloc_maxlevels) * 2 - 2;
>  	/* space needed by-size freespace btree */
> -	min_free += min(cnt_level + 1, mp->m_alloc_maxlevels) * 2 - 2;
> +	min_free += min(cnt_level + levels, mp->m_alloc_maxlevels) * 2 - 2;
>  	/* space needed reverse mapping used space btree */
> -	if (xfs_has_rmapbt(mp))
> -		min_free += min(rmap_level + 1, mp->m_rmap_maxlevels) * 2 - 2;
> +	if (xfs_has_rmapbt(mp)) {
> +		min_free += min(rmap_level + levels,
> +				mp->m_rmap_maxlevels) * 2 - 2;
> +	}
>  	return min_free;
>  }
>  
> +unsigned int
> +xfs_alloc_min_freelist(
> +	struct xfs_mount	*mp,
> +	struct xfs_perag	*pag)
> +{
> +	return __xfs_alloc_min_freelist(mp, pag, 0);
> +}
> +
>  /*
>   * Check if the operation we are fixing up the freelist for should go ahead or
>   * not. If we are freeing blocks, we always allow it, otherwise the allocation
> -- 
> 2.55.0
> 
>