Apache memory usage never goes above 5%

Question

I'm deploying an application that uses ImageMagick into VPS server. I tested in on two different OS: Centos6 and Ubuntu Server 12.04.

On Centos6, the application is working properly and when accessing ImageMagick script, memory usage can goes above 90% (FYI, both OS and VPS instance are using 512MB memory package). However, when I tried the same script, it never goes above 5-6.2%.

top result on ubuntu server:

PID  USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
1816 userx     20   0  341m  24m 5260 D 40.8  5.0   0:13.85 apache2

top result on centos server:

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
15798 ariefbay  20   0  183m 155m 5684 R 99.8 31.2   0:05.96 httpd

This memory limitation resulted in very long process. I need it to be fast and since this will be a limited usage server, I don't mind if it consume the whole memory.

I've tried the following step:

• adding RLimitMEM to /etc/apache2/apache2.conf

  RLimitMEM max max
  

• setting ulimit -l unlimited

• adding config into /etc/security/limits.conf:

  userx - rtprio 99
  userx - memlock unlimited
  userx - nice -10
  

  • note: apache2 process are running as userx.

  • this is working ok as proved by ulimit -a:

    userx@do:/etc/apache2$ ulimit -a
    core file size          (blocks, -c) 0
    data seg size           (kbytes, -d) unlimited
    scheduling priority             (-e) 30
    file size               (blocks, -f) unlimited
    pending signals                 (-i) 3861
    max locked memory       (kbytes, -l) unlimited
    max memory size         (kbytes, -m) unlimited
    open files                      (-n) 1024
    pipe size            (512 bytes, -p) 8
    POSIX message queues     (bytes, -q) 819200
    real-time priority              (-r) 99
    stack size              (kbytes, -s) 8192
    cpu time               (seconds, -t) unlimited
    max user processes              (-u) 3861
    virtual memory          (kbytes, -v) unlimited
    file locks                      (-x) unlimited
    

• I can also see that the memory settings are working fine by looking at /proc/pic/limits:

  userx@do:/etc/apache2$ cat /proc/1811/limits
  Limit                     Soft Limit           Hard Limit           Units
  Max cpu time              unlimited            unlimited            seconds
  Max file size             unlimited            unlimited            bytes
  Max data size             unlimited            unlimited            bytes
  Max stack size            8388608              unlimited            bytes
  Max core file size        0                    unlimited            bytes
  Max resident set          unlimited            unlimited            bytes
  Max processes             3861                 3861                 processes
  Max open files            8192                 8192                 files
  Max locked memory         unlimited            unlimited            bytes
  Max address space         unlimited            unlimited            bytes
  Max file locks            unlimited            unlimited            locks
  Max pending signals       3861                 3861                 signals
  Max msgqueue size         819200               819200               bytes
  Max nice priority         30                   30
  Max realtime priority     99                   99
  Max realtime timeout      unlimited            unlimited            us
  

Did I do something wrong? what should I do to remedy this problem on ubuntu?