Checking whether Class.new makes permanent refs (with cribbing from https://gist.github.com/rjackson/5071864 h/t @nevern02)

profile.rb

def m(m)
    puts m
    puts "  Currently at: #{`ps -o rss= -p #$$`.to_i / 1024} MB"
    puts "  #{GC.stat.inspect}"
end

m 'Started';

10_000_000.times { Class.new }
m 'Made 10,000,000 (unstored) objects'

GC.start
m 'Ran GC'

a = []
10_000_000.times { a << Class.new }
m 'Made 10,000,000 (stored) objects'

a = nil
m 'Dereferenced the array'

GC.start
m 'Ran GC'

run.txt

Started
  Currently at: 5 MB
  {:count=>3, :heap_used=>77, :heap_length=>77, :heap_increment=>0, :heap_live_num=>15152, :heap_free_num=>16321, :heap_final_num=>3}
Made 10,000,000 (unstored) objects
  Currently at: 12 MB
  {:count=>1144, :heap_used=>77, :heap_length=>77, :heap_increment=>0, :heap_live_num=>7536, :heap_free_num=>23941, :heap_final_num=>0}
Ran GC
  Currently at: 12 MB
  {:count=>1145, :heap_used=>77, :heap_length=>77, :heap_increment=>0, :heap_live_num=>7314, :heap_free_num=>24158, :heap_final_num=>0}
Made 10,000,000 (stored) objects
  Currently at: 2021 MB
  {:count=>1271, :heap_used=>48942, :heap_length=>87251, :heap_increment=>38309, :heap_live_num=>19815516, :heap_free_num=>191975, :heap_final_num=>0}
Dereferenced the array
  Currently at: 2021 MB
  {:count=>1271, :heap_used=>48942, :heap_length=>87251, :heap_increment=>38309, :heap_live_num=>19815516, :heap_free_num=>191975, :heap_final_num=>0}
Ran GC
  Currently at: 673 MB
  {:count=>1272, :heap_used=>31894, :heap_length=>87251, :heap_increment=>38309, :heap_live_num=>7314, :heap_free_num=>13030950, :heap_final_num=>0}