Limit Time Machine size on SMB server

Sold my old Time Capsule, too slow, now using HP machine running Ubuntu VM with Samba 4.8 as Time Machine server - much faster backup and restore. Setup was relatively easy and Macs able to find it and configure backup.

I'm thinking of assigning the same VM as file server instead of using a second VM, and want to limit TM from taking up all available space. I have read that Synology was able to do this, so can FreeNAS and old Netatalk (AFP) on Linux. I wonder if it is possible to do the same with my setup (Ubuntu/SMB) without creating additional partitions?

By the way, I am also aware of com.apple.TimeMachine MaxSize option, but like to set the limit on server side if possible.