I am running unicorn on Ubuntu 11, Rails 3.0, and Ruby 1.8.7. It is an 8 core ec2 box, and I am running 15 workers. CPU never seems to get pinned, and I seem to be handling requests pretty nicely. My question concerns memory usage, and what concerns I should have with what I am seeing. (if any) Here is the scenario: Under constant load (about 15 reqs/sec coming in from nginx), over the course of an hour, each server in the 3 server cluster loses about 100MB / hour. This is a linear slope for about 6 hours, then it appears to level out, but still maybe appear to lose about 10MB/hour. If I drop my page caches using the linux command echo 1 /proc/sys/vm/drop_caches, the available free memory shoots back up to what it was when I started the unicorns, and the memory loss pattern begins again over the hours. Before: total used free shared buffers cached Mem: 7130244 5005376 2124868 0 113628 422856 -/+ buffers/cache: 4468892 2661352 Swap: 33554428 0 33554428 After: total used free shared buffers cached Mem: 7130244 4467144 2663100 0 228 11172 -/+ buffers/cache: 4455744 2674500 Swap: 33554428 0 33554428 My Ruby code does use memoizations and I'm assuming Ruby/Rails/Unicorn is keeping its own caches... what I'm wondering is should I be worried about this behaviour? FWIW, my Unicorn config: worker_processes 15 listen "#{CAPISTRANO_ROOT}/shared/pids/unicorn_socket", :backlog = 1024 listen 8080, :tcp_nopush = true timeout 180 pid "#{CAPISTRANO_ROOT}/shared/pids/unicorn.pid" GC.respond_to?(:copy_on_write_friendly=) and GC.copy_on_write_friendly = true before_fork do |server, worker| STDERR.puts "XXXXXXXXXXXXXXXXXXX BEFORE FORK" print_gemfile_location defined?(ActiveRecord::Base) and ActiveRecord::Base.connection.disconnect! defined?(Resque) and Resque.redis.client.disconnect old_pid = "#{CAPISTRANO_ROOT}/shared/pids/unicorn.pid.oldbin" if File.exists?(old_pid) && server.pid != old_pid begin Process.kill("QUIT", File.read(old_pid).to_i) rescue Errno::ENOENT, Errno::ESRCH # already killed end end File.open("#{CAPISTRANO_ROOT}/shared/pids/unicorn.pid.ok", "w"){|f| f.print($$.to_s)} end after_fork do |server, worker| defined?(ActiveRecord::Base) and ActiveRecord::Base.establish_connection defined?(Resque) and Resque.redis.client.connect end Is there a need to experiment enforcing more stringent garbage collection using OobGC (http://unicorn.bogomips.org/Unicorn/OobGC.html)? Or is this just normal behaviour, and when/as the system needs more memory, it will empty the caches by itself, without me manually running that cache command? Basically, is this normal, expected behaviour? tia