title: Kill apache processes when memory usage reaches 90%
body: <p>My situation is following:
  We run Magento Professional on a 15Gb ram instance, rackspace.</p>
  
  <p>When running htop, we could see that 'apache2 -k start' keeps spawning more child processes, someone them eats ~900Mb of memory. </p>
  
  <p>When memory is almost used up, all sites time out or become very slow.
  When memory is all used up, it seems that some of these processes got killed to free memory.</p>
  
  <p>Then the same procedures happen.</p>
  
  <p>My question is, could we setup ubuntu / apache to kill off child processes and free memory when memory usage reaches 85-90% ? </p>