Re: [PATCH 6/7] xfs: improve the comments in xfs_max_open_zones

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

On Wed, Jul 16, 2025 at 02:54:06PM +0200, Christoph Hellwig wrote:
> Describe the rationale for the decisions a bit better.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_zone_alloc.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/xfs/xfs_zone_alloc.c b/fs/xfs/xfs_zone_alloc.c
> index d9e2b1411434..c1f053f4a82a 100644
> --- a/fs/xfs/xfs_zone_alloc.c
> +++ b/fs/xfs/xfs_zone_alloc.c
> @@ -1114,24 +1114,27 @@ xfs_get_zone_info_cb(
>  }
>  
>  /*
> - * Calculate the max open zone limit based on the of number of
> - * backing zones available
> + * Calculate the max open zone limit based on the of number of backing zones
> + * available.
>   */
>  static inline uint32_t
>  xfs_max_open_zones(
>  	struct xfs_mount	*mp)
>  {
>  	unsigned int		max_open, max_open_data_zones;
> +
>  	/*
> -	 * We need two zones for every open data zone,
> -	 * one in reserve as we don't reclaim open zones. One data zone
> -	 * and its spare is included in XFS_MIN_ZONES.
> +	 * We need two zones for every open data zone, one in reserve as we
> +	 * don't reclaim open zones.  One data zone and its spare is included
> +	 * in XFS_MIN_ZONES to support at least one user data writer.
>  	 */
>  	max_open_data_zones = (mp->m_sb.sb_rgcount - XFS_MIN_ZONES) / 2 + 1;
>  	max_open = max_open_data_zones + XFS_OPEN_GC_ZONES;
>  
>  	/*
> -	 * Cap the max open limit to 1/4 of available space
> +	 * Cap the max open limit to 1/4 of available space.  Without this we'd
> +	 * run out of easy reclaim targets too quickly and storage devices don't
> +	 * handle huge numbers of concurrent write streams overly well.
>  	 */
>  	return clamp(max_open, XFS_MIN_OPEN_ZONES, mp->m_sb.sb_rgcount / 4);
>  }
> -- 
> 2.47.2
> 
>