Simple G1GC tuning

// This is the working definition of a server class machine:
// >= 2 physical CPU's and >=2GB of memory, with some fuzz
// because the graphics memory (?) sometimes masks physical memory.
// If you want to change the definition of a server class machine
// on some OS or platform, e.g., >=4GB on Windows platforms,
// then you'll have to parameterize this method based on that state,
// as was done for logical processors here, or replicate and
// specialize this method for each platform.  (Or fix os to have
// some inheritance structure and use subclassing.  Sigh.)
// If you want some platform to always or never behave as a server
// class machine, change the setting of AlwaysActAsServerClassMachine
// and NeverActAsServerClassMachine in globals*.hpp.
bool os::is_server_class_machine() {

void GCConfig::select_gc_ergonomically() {
  if (os::is_server_class_machine()) {
#if INCLUDE_G1GC
    FLAG_SET_ERGO_IF_DEFAULT(bool, UseG1GC, true);
#elif INCLUDE_PARALLELGC
    FLAG_SET_ERGO_IF_DEFAULT(bool, UseParallelGC, true);
#elif INCLUDE_SERIALGC
    FLAG_SET_ERGO_IF_DEFAULT(bool, UseSerialGC, true);
#endif
  } else {
#if INCLUDE_SERIALGC
    FLAG_SET_ERGO_IF_DEFAULT(bool, UseSerialGC, true);
#endif
  }
}