Ceph (deep) scrub daemon
This far from done "Ceph Scrub Daemon" fires off scrubs on PGs and prioritizes PGs by last(_deep)_scrub timestamp.
It tries to limit the number of simultaneous scrubs, but this logic may well be flawed.
Runs shallow scrubs by default. Use the -D or --deep-scrub argument to make it run deep scrubs.
All the magic is in the run function of the PGScrub class. All the rest is scaffolding. :-)
There may be dragons.