title: JVM enough memory but frequency full gc
body: <p>JVM Options:
  -Xms512M -Xmx512M -XX:PermSize=70M -XX:MaxPermSize=70M</p>
  
  <p><strong>jstat -gc 8260 5000</strong></p>
  
  <p>S0C:512.0  S1C:512.0   S0U:0.0    S1U:0.0   EC:174080.0   EU:0.0    OC:349696.0   OU:45191.1   PC:71680.0   PU:34882.2   YGC:2216225   YGCT:6754.909   FGC:2216144   FGCT:160651.466   GCT:167406.375</p>
  
  <p>S0C:512.0  S1C:512.0   S0U:0.0    S1U:64.0  EC:174080.0   EU:0.0    OC:349696.0   OU:45187.3   PC:71680.0   PU:34882.2   YGC:2216253   YGCT:6755.047   FGC:2216172   FGCT:160653.488   GCT:167408.535</p>
  
  <p>S0C:512.0  S1C:512.0   S0U:0.0    S1U:128.0 EC:174080.0   EU:0.0    OC:349696.0   OU:45189.6   PC:71680.0   PU:34882.2   YGC:2216281   YGCT:6755.180   FGC:2216200   FGCT:160655.542   GCT:167410.721</p>
  
  <p>S0C:512.0  S1C:512.0   S0U:0.0    S1U:0.0   EC:174080.0   EU:1775.6 OC:349696.0   OU:45187.3   PC:71680.0   PU:34882.2   YGC:2216308   YGCT:6755.309   FGC:2216227   FGCT:160657.627   GCT:167412.936</p>
  
  <p>S0C:512.0  S1C:512.0   S0U:128.0  S1U:0.0   EC:174080.0   EU:0.0    OC:349696.0   OU:45187.3   PC:71680.0   PU:34882.2   YGC:2216336   YGCT:6755.444   FGC:2216255   FGCT:160659.701   GCT:167415.146</p>
  
  <p>Why JVM frequency full gc happened?</p>