Passenger/Ruby memory usage goes out of control on Ubuntu

The last few days Passenger has been eating up loads of memory on my Slicehost VPS, and I can't seem to get it under control. It runs fine for a few hours, and then all of a sudden spawns tons of rubies. I thought Apache was the problem, so I switched to Nginx, but the problem persists. Here's a dump of top:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                                       
 5048 avishai   20   0  160m  43m 1192 S    0 10.9   0:00.77 ruby1.8                                                                                                                                                                        
 5102 avishai   20   0  151m  41m 1392 S    0 10.6   0:00.07 ruby1.8                                                                                                                                                                        
 5091 avishai   20   0  153m  30m 1400 D    0  7.6   0:00.27 ruby1.8                                                                                                                                                                        
 5059 avishai   20   0  158m  27m 1344 D    0  7.0   0:00.64 ruby1.8                                                                                                                                                                        
 4809 avishai   20   0  161m  27m 1208 D    0  6.9   0:06.65 ruby1.8    开发者_StackOverflow                                                                                                                                                                    
 4179 avishai   20   0  162m  23m 1140 D    0  5.9   0:25.25 ruby1.8                                                                                                                                                                        
 5063 avishai   20   0  159m  23m 1200 D    0  5.9   0:00.65 ruby1.8                                                                                                                                                                        
 5044 avishai   20   0  159m  12m 1172 S    0  3.3   0:00.79 ruby1.8                                                                                                                                                                        
 5113 avishai   20   0  149m 9.8m 1576 D    0  2.5   0:00.00 ruby1.8                                                                                                                                                                        
 5076 avishai   20   0  155m 9.8m 1128 S    0  2.5   0:00.33 ruby1.8                                                                                                                                                                        
 3269 mysql     20   0  239m 5356 2156 S    0  1.3   0:00.35 mysqld                                                                                                                                                                         
 3510 root      20   0 49948 3580  736 S    0  0.9   1:01.86 ruby1.8                                                                                                                                                                        
 4792 root      20   0 98688 3560  644 S    0  0.9   0:00.84 ruby1.8                                                                                                                                                                        
 4799 avishai   20   0  148m 2204  600 S    0  0.5   0:01.64 ruby1.8                                                                                                                                                                        
 3508 root      20   0  295m 1972 1044 S    0  0.5   0:35.77 PassengerHelper                                                                                                                                                                
 3562 nobody    20   0 39776  964  524 D    0  0.2   0:00.82 nginx                                                                                                                                                                          
 3561 nobody    20   0 39992  948  496 D    0  0.2   0:00.72 nginx                                                                                                                                                                          
 4238 avishai   20   0 19144  668  456 R    0  0.2   0:00.06 top                                                                                                                                                                            
 3293 syslog    20   0  123m  636  420 S    0  0.2   0:00.06 rsyslogd                                                                                                                                                                       
 3350 nobody    20   0  139m  432  220 S    0  0.1   0:00.05 memcached                                                                                                                                                                      
 3364 redis     20   0 50368  412  300 S    0  0.1   0:00.33 redis-server                                                                                                                                                                   
 1575 avishai   20   0 51912  324  216 S    0  0.1   0:00.00 sshd                                                                                                                                                                           
 3513 nobody    20   0 72272  192  160 S    0  0.0   0:00.02 PassengerLoggin                                                                                                                                                                
 3330 root      20   0 21012  180  124 S    0  0.0   0:00.00 cron                                                                                                                                                                           
 3335 root      20   0 49184  152  144 S    0  0.0   0:00.01 sshd                                                                                                                                                                           
    1 root      20   0 23500   92   88 S    0  0.0   0:00.08 init                                                                                                                                                                           
 1573 root      20   0 51764   88   80 S    0  0.0   0:00.00 sshd                                                                                                                                                                           
 3505 root      20   0 89044   84   80 S    0  0.0   0:00.00 PassengerWatchd                                                                                                                                                                
 3319 root      20   0  5996   68   64 S    0  0.0   0:00.00 getty                                                                                                                                                                          
 3323 root      20   0  6000   68   64 S    0  0.0   0:00.00 getty                                                                                                                                                                          
 3325 root      20   0  5996   68   64 S    0  0.0   0:00.00 getty                                                                                                                                                                          
 3326 root      20   0  6000   68   64 S    0  0.0   0:00.00 getty                                                                                                                                                                          
 3328 root      20   0  5996   68   64 S    0  0.0   0:00.00 getty                                                                                                                                                                          
 3383 root      20   0  5996   68   64 S    0  0.0   0:00.01 getty 

Here's my environment:

RubyGems Environment:
  - RUBYGEMS VERSION: 1.6.2
  - RUBY VERSION: 1.8.7 (2011-02-18 patchlevel 334) [x86_64-linux]
  - INSTALLATION DIRECTORY: /home/avishai/.rvm/gems/ruby-1.8.7-p334
  - RUBY EXECUTABLE: /home/avishai/.rvm/rubies/ruby-1.8.7-p334/bin/ruby
  - EXECUTABLE DIRECTORY: /home/avishai/.rvm/gems/ruby-1.8.7-p334/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /home/avishai/.rvm/gems/ruby-1.8.7-p334
     - /home/avishai/.rvm/gems/ruby-1.8.7-p334@global
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
     - "gem" => "--no-ri --no-rdoc"
     - :sources => ["http://gems.rubyforge.org", "http://gems.github.com"]
  - REMOTE SOURCES:
     - http://gems.rubyforge.org
     - http://gems.github.com

---

It appears you have a lot of instances running. Try limiting this as is appropriate for your system.

passenger_max_pool_size 2

I tend to go for one instance per 128MB of RAM you have.

Full documentation: http://www.modrails.com/documentation/Users%20guide%20Nginx.html#PassengerMaxPoolSize