DB schema for storing the process tree of linux
The design should be according to your requirements. If your requirement includes to store only some columnar data that are mostly required (mostly not null) then use tables with relations (foreign keys). If you just need some logging with situational tree structure data then use JSONB. 
For example, suppose that you store io_counters when counters are higher than some point, then use JSON.
I presuppose you use minimum postgresql 9-4.