Use case for zfs_dirty_data_max_percent and zfs_dirty_data_max_max_percent parameters

[rkojedzinszky]

I was reading documentation, code, and for me it is not clear why these two sysctls exist. It seems that in arc_init() both are processed, howewer later anyone can simply set zfs_dirty_data_max without checking actual limits. Also, on FreeBSD, max_percent and max_max_percent are tunables, they can only be set on module load. From my understanding, one max parameter would be simply enough. If one could provide a use case for both settings, I would appreciate that.