Test Ruby's ability to release memory back to system.

output.txt

Ruby 1.9.3-p392
===========================================================
All memory used before 1st run                     - 7 MB
Memory consumed by 1st run of eat_up_memory        - 445 MB
All memory used before 2nd run                     - 452 MB
Memory consumed by 2nd run of eat_up_memory        - 20 MB
All memory used before 3rd run                     - 472 MB
Memory consumed by 3rd run of eat_up_memory        - 5 MB
Memory used before explicit GC.start               - 478 MB
Memory used after explicit GC.start                - 284 MB

Ruby 2.0.0-p0
===========================================================
All memory used before 1st run                     - 8 MB
Memory consumed by 1st run of eat_up_memory        - 468 MB
All memory used before 2nd run                     - 476 MB
Memory consumed by 2nd run of eat_up_memory        - 84 MB
All memory used before 3rd run                     - 561 MB
Memory consumed by 3rd run of eat_up_memory        - 19 MB
Memory used before explicit GC.start               - 580 MB
Memory used after explicit GC.start                - 511 MB

Ruby 2.0.0-p0 
RUBY_FREE_MIN=200000 RUBY_GC_MALLOC_LIMIT=60000000
===========================================================
All memory used before 1st run                     - 8 MB
Memory consumed by 1st run of eat_up_memory        - 553 MB
All memory used before 2nd run                     - 561 MB
Memory consumed by 2nd run of eat_up_memory        - 0 MB
All memory used before 3rd run                     - 562 MB
Memory consumed by 3rd run of eat_up_memory        - 25 MB
Memory used before explicit GC.start               - 588 MB
Memory used after explicit GC.start                - 406 MB

test_releasing_of_memory.rb

require 'securerandom'

def memory_usage
  `ps -o rss= -p #{Process.pid}`.to_i
end

def profile_memory(comment)
  before = memory_usage

  block_given? ? yield : before = 0

  puts "#{comment.ljust(50)} - #{(memory_usage - before) / 1024} MB"
end

def eat_up_memory
  strings = []

  1_000_000.times do
    strings << SecureRandom.base64(255)
  end

  nil
end

['1st','2nd','3rd'].each do |count|
  profile_memory "All memory used before #{count} run"
  profile_memory("Memory consumed by #{count} run of eat_up_memory") do
    eat_up_memory
  end
end

profile_memory "Memory used before explicit GC.start"
GC.start
profile_memory "Memory used after explicit GC.start"