title: Linux free shows high memory usage but top does not
body: <p>On RedHat Linux 6.2 I'm running <code>free -m</code> and it shows nearly all <code>8GB</code> used</p>
  
  <pre><code>             total       used       free     shared    buffers     cached
  Mem:          7989       7734        254          0         28       7128
  -/+ buffers/cache:        578       7411
  Swap:         4150          0       4150
  </code></pre>
  
  <p>But at the same time in <code>top -M</code> I cannot see any processes using all this memory:</p>
  
  <pre><code>top - 16:03:34 up  4:10,  2 users,  load average: 0.08, 0.04, 0.01
  Tasks: 169 total,   1 running, 163 sleeping,   5 stopped,   0 zombie
  Cpu(s):  0.7%us,  0.3%sy,  0.0%ni, 98.6%id,  0.4%wa,  0.0%hi,  0.0%si,  0.0%st
  Mem:  7989.539M total, 7721.570M used,  267.969M free,   28.633M buffers
  Swap: 4150.992M total,    0.000k used, 4150.992M free, 7115.312M cached
  
    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
   1863 sroot     20   0  398m  24m 9.8m S  0.3  0.3   3:12.87 App1
      1 sroot     20   0  2864 1392 1180 S  0.0  0.0   0:00.91 init
      2 sroot     20   0     0    0    0 S  0.0  0.0   0:00.00 kthreadd
      3 sroot     RT   0     0    0    0 S  0.0  0.0   0:00.07 migration/0
      4 sroot     20   0     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/0
      5 sroot     RT   0     0    0    0 S  0.0  0.0   0:00.00 migration/0
      6 sroot     RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/0
      7 sroot     RT   0     0    0    0 S  0.0  0.0   0:00.08 migration/1
      8 sroot     RT   0     0    0    0 S  0.0  0.0   0:00.00 migration/1
  </code></pre>
  
  <p>I also tried this <a href="http://www.pixelbeat.org/scripts/ps_mem.py">ps mem script</a> but it onlt shows about 400MB memory being used.</p>