I attached the gzipped results of
jcmd <pid> GC.class_stats
You'll notice 1 million ..._run_closure... classes.
To give some background for our setup...."mainJobs" is run in parameterized job that run on each branch push. It creates a different folder for each branch, and creates and triggers a "jobs" job in that folder that runs and produces the jobs in that directory. Periodically, folders for deleted branches are removed.