If you use systemd you can assign services to slices which can be assigned cgroup resource reservations / limits. I don't think any distro does too much with th

If you use systemd you can assign services to slices which can be assigned cgroup resource reservations / limits. I don't think any distro does too much with this out of the box yet (IIRC by default all services run under a single "system" slice, and user sessions under a user slice), but it should be possible to run an "emergency environment" slice in which the processes are always guaranteed some small amount of resources necessary to recover.