jvm 内存

jint Universe::initialize_heap() {

  if (UseParallelGC) {
#ifndef SERIALGC
    Universe::_collectedHeap = new ParallelScavengeHeap();
#else  // SERIALGC
    fatal("UseParallelGC not supported in java kernel vm.");
#endif // SERIALGC

  } else if (UseG1GC) {
#ifndef SERIALGC
    G1CollectorPolicy* g1p = new G1CollectorPolicy_BestRegionsFirst();
    G1CollectedHeap* g1h = new G1CollectedHeap(g1p);
    Universe::_collectedHeap = g1h;
#else  // SERIALGC
    fatal("UseG1GC not supported in java kernel vm.");
#endif // SERIALGC

  } else {
    GenCollectorPolicy *gc_policy;

    if (UseSerialGC) {
      gc_policy = new MarkSweepPolicy();
    } else if (UseConcMarkSweepGC) {
#ifndef SERIALGC
      if (UseAdaptiveSizePolicy) {
        gc_policy = new ASConcurrentMarkSweepPolicy();
      } else {
        gc_policy = new ConcurrentMarkSweepPolicy();
      }
#else   // SERIALGC
    fatal("UseConcMarkSweepGC not supported in java kernel vm.");
#endif // SERIALGC
    } else { // default old generation
      gc_policy = new MarkSweepPolicy();
    }

    Universe::_collectedHeap = new GenCollectedHeap(gc_policy);
  }

  jint status = Universe::heap()->initialize();
  if (status != JNI_OK) {
    return status;
  }

#ifdef _LP64
  if (UseCompressedOops) {
    // Subtract a page because something can get allocated at heap base.
    // This also makes implicit null checking work, because the
    // memory+1 page below heap_base needs to cause a signal.
    // See needs_explicit_null_check.
    // Only set the heap base for compressed oops because it indicates
    // compressed oops for pstack code.
    if (PrintCompressedOopsMode) {
      tty->cr();
      tty->print("heap address: "PTR_FORMAT, Universe::heap()->base());
    }
    if ((uint64_t)Universe::heap()->reserved_region().end() > OopEncodingHeapMax) {
      // Can't reserve heap below 32Gb.
      Universe::set_narrow_oop_base(Universe::heap()->base() - os::vm_page_size());
      Universe::set_narrow_oop_shift(LogMinObjAlignmentInBytes);
      if (PrintCompressedOopsMode) {
        tty->print(", Compressed Oops with base: "PTR_FORMAT, Universe::narrow_oop_base());
      }
    } else {
      Universe::set_narrow_oop_base(0);
      if (PrintCompressedOopsMode) {
        tty->print(", zero based Compressed Oops");
      }
#ifdef _WIN64
      if (!Universe::narrow_oop_use_implicit_null_checks()) {
        // Don't need guard page for implicit checks in indexed addressing
        // mode with zero based Compressed Oops.
        Universe::set_narrow_oop_use_implicit_null_checks(true);
      }
#endif //  _WIN64
      if((uint64_t)Universe::heap()->reserved_region().end() > NarrowOopHeapMax) {
        // Can't reserve heap below 4Gb.
        Universe::set_narrow_oop_shift(LogMinObjAlignmentInBytes);
      } else {
        Universe::set_narrow_oop_shift(0);
        if (PrintCompressedOopsMode) {
          tty->print(", 32-bits Oops");
        }
      }
    }
    if (PrintCompressedOopsMode) {
      tty->cr();
      tty->cr();
    }
  }
  assert(Universe::narrow_oop_base() == (Universe::heap()->base() - os::vm_page_size()) ||
         Universe::narrow_oop_base() == NULL, "invalid value");
  assert(Universe::narrow_oop_shift() == LogMinObjAlignmentInBytes ||
         Universe::narrow_oop_shift() == 0, "invalid value");
#endif

  // We will never reach the CATCH below since Exceptions::_throw will cause
  // the VM to exit if an exception is thrown during initialization

  if (UseTLAB) {
    assert(Universe::heap()->supports_tlab_allocation(),
           "Should support thread-local allocation buffers");
    ThreadLocalAllocBuffer::startup_initialization();
  }
  return JNI_OK;
}