Today I can set the setting to 0, which allows full use of the hard disk as cache. Furthermore, you can set the cache to a fixed size in megabytes.
As an extension of this setting, we would like to be able to set negative values. This should result in the maximum size of the cache equal to "size of the hard disk" minus the value of the config.pro setting.
This would make it easy to ensure that a minimum of disk space would always remain free, regardless of the hard drives used.
Today we have the problem that some computers have 256 GB and some 512 GB hard disks installed. If you want to prevent caches from becoming corrupted due to a full hard disk, the value of the setting dm_cache_limit must be limited to 261120 MB (= 255 GB). But the computers with 512 GB hard disks would allow much larger caches.