Issue #9134 has been reported by sam.saffron (Sam Saffron). ---------------------------------------- Bug #9134: RUBY_HEAP_MIN_SLOTS does not work correctly in Ruby 2.0 https://bugs.ruby-lang.org/issues/9134 Author: sam.saffron (Sam Saffron) Status: Open Priority: Normal Assignee: Category: Target version: ruby -v: 2.0.0 Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN sam@ubuntu:~/Source$ rbenv shell ruby-head sam@ubuntu:~/Source$ RUBY_HEAP_MIN_SLOTS=$(( 408*1000 )) ruby -e "puts GC.stat[:heap_length]" 1000 sam@ubuntu:~/Source$ rbenv shell 2.0.0-p247 sam@ubuntu:~/Source$ RUBY_HEAP_MIN_SLOTS=$(( 408*1000 )) ruby -e "puts GC.stat[:heap_length]" 1803 RUBY_HEAP_MIN_SLOTS is over committing heap space in 2.0 , this works perfectly fine in Ruby head. --- This only affects Ruby 2.0 not Ruby head. The over growth happens on first GC run, it grows the heaps to the correct size, but then quickly grows it again. -- http://bugs.ruby-lang.org/