Additionally we don't even boot on JRuby today, I wish we did but it is hard to justify effort here.
Just by playing around with RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR you can reduce memory consumption quite a bit.
https://github.com/discourse/discourse_docker/blob/master/te...
RUBY_GC_HEAP_GROWTH_MAX_SLOTS is critical without it you get way too much bloat. The default is very problematic I discussed this with ko1 but not sure if we can get a better default in for 2.4.
what is the blocking issue there?
For people starting out that is not so much a problem, but if you have moderate to large traffic you need a lot of machines just for the RAM. This is coupled with the fact that many Ruby libraries eschew streaming of files and connections and put things straight into memory despite Ruby having excellent block constructs that easily allow chunking/streaming. So apps also spike in memory and they need a large overhead as well.