Enabling YJIT via Template Doesn't Work

Contribute Bug
1

Hi there,

I run a self hosted Discourse install (2026.5.0-latest). Today I tried to turn YJIT on. I added "templates/enable-ruby-yjit.yml" to containers/app.yml and rebuilt the app.

After the rebuild was done, something interesting happened. Inside the Docker container, I ran env | grep RUBY_YJIT_ENABLE and got RUBY_YJIT_ENABLE=1. So far so good. But then I ran sudo -u discourse RAILS_ENV=production bundle exec rails runner 'puts "YJIT enabled: #{RubyVM::YJIT.enabled?}"; puts RUBY_DESCRIPTION' … I got:

YJIT enabled: false

ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]

So YJIT was not enabled, despite adding the enable-ruby-yjit.yml template. Then, when I ran sudo -u discourse RAILS_ENV=production bundle exec rails runner 'puts "GlobalSetting.yjit_enabled=#{GlobalSetting.yjit_enabled}"' I got GlobalSetting.yjit_enabled= — a nil value!

Anyway, after futzing around with it a bit more, I finally got YJIT enabled by adding the following to containers/app.yml:

env:
  DISCOURSE_YJIT_ENABLED: true

I’m sure there’s a bug somewhere (GlobalSetting.yjit_enabled shouldn’t ever return nil) but setting the env variable worked, and I hope someone Googling for this will find this topic.

לייק 1
2

Isn’t that a misdiagnose? You are checking the ENV of a brand new spawned ruby proccess instead of the one running the actual web server.

If you inspect the /proc/<pid>/environ of the Pitchfork mold process you will see the YJIT env var there.

root@raspberrypi5:/var/discourse# cat /proc/3331660/environ | tr '\0' '\n' | grep -i yjit
RUBY_YJIT_ENABLE=1