MemoryMash.php

class MemoryMash {
    public function mash() {
        str_pad('', $this->getMaxMemory());
    }
    
    private function getMaxMemory() {
        $memoryLimit = ini_get('memory_limit');
        if ($memoryLimit != -1) {
            $memoryLimit = $this->return_bytes($memoryLimit);
        } else {
            # linuxy only, meh
            exec('vmstat -s', $vmstat);
            preg_match('/(\d+) (\w)/', $vmstat[0], $matches);
            $memoryLimit = $this->return_bytes($matches[1] . $matches[2]);
        }
        
        return $memoryLimit;
    }
    
    #http://php.net/manual/en/function.ini-get.php#refsect1-function.ini-get-examples
    private function return_bytes($val) {
        $val = trim($val);
        $last = strtolower($val[strlen($val)-1]);
        switch($last) {
            // The 'G' modifier is available since PHP 5.1.0
            case 'g':
                $val *= 1024;
            case 'm':
                $val *= 1024;
            case 'k':
                $val *= 1024;
        }
        return $val;
    }
}

exhaust memory_limit (or actual memory on the server, maybe?)