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