[Bug #21394] There are two ways to make RubyVM::InstructionSequence.new raise which would cause the options->scopes to leak memory: 1. Passing in any (non T_FILE) object where the to_str raises. 2. Passing in a T_FILE object where String#initialize_dup raises. This is because rb_io_path dups the string. Example 1: 10.times do 100_000.times do RubyVM::InstructionSequence.new(nil) rescue TypeError end puts `ps -o rss= -p #{$$}` end Before: 13392 17104 20256 23920 27264 30432 33584 36752 40032 43232 After: 9392 11072 11648 11648 11648 11712 11712 11712 11744 11744 Example 2: require "tempfile" MyError = Class.new(StandardError) String.prepend(Module.new do def initialize_dup(_) if $raise_on_dup raise MyError else super end end end) Tempfile.create do |f| 10.times do 100_000.times do $raise_on_dup = true RubyVM::InstructionSequence.new(f) rescue MyError else raise "MyError was not raised during RubyVM::InstructionSequence.new" end puts `ps -o rss= -p #{$$}` ensure $raise_on_dup = false end end Before: 14080 18512 22000 25184 28320 31600 34736 37904 41088 44256 After: 12016 12464 12880 12880 12880 12912 12912 12912 12912 12912