title: Sidekiq does not release memory after job is processed
body: <p>I have a ruby on rails app, where we validate records from huge excel files(200k records) in background via sidekiq. We also use docker and hence a separate container for sidekiq. When the sidekiq is up, memory used is approx 120Mb, but as the validation worker begins, the memory reaches upto 500Mb (that's after a lot of optimisation).
  Issue is even after the job is processed, the memory usage stays at 500Mb and is never freed, not allowing any new jobs to be added.
  I manually start garbage collection using GC.start after every 10k records and also after the job is complete, but still no help.</p>