[0x0000ffff93e3acc0] Thread::allocate(unsigned long, bool, MemoryType)+0x348
[0x0000ffff9377a498] CompileBroker::make_compiler_thread(char const*, CompileQueue*, CompilerCounters*, AbstractCompiler*, Thread*)+0x120
[0x0000ffff9377ce98] CompileBroker::init_compiler_threads(int, int)+0x148
[0x0000ffff9377d400] CompileBroker::compilation_init()+0xc8
                             (malloc=37KB type=Thread #12)

# hotspot/src/share/vm/compiler/CompileBroker.cpp
void CompileBroker::compilation_init() {
  ......
  // No need to initialize compilation system if we do not use it.
  if (!UseCompiler) {
    return;
  }
#ifndef SHARK
  // Set the interface to the current compiler(s).
  int c1_count = CompilationPolicy::policy()->compiler_count(CompLevel_simple);
  int c2_count = CompilationPolicy::policy()->compiler_count(CompLevel_full_optimization);
  ......
  // Start the CompilerThreads
  init_compiler_threads(c1_count, c2_count);
  ......
}

# hotspot/src/share/vm/runtime/arguments.cpp
void Arguments::set_tiered_flags() {
  // With tiered, set default policy to AdvancedThresholdPolicy, which is 3.
  if (FLAG_IS_DEFAULT(CompilationPolicyChoice)) {
    FLAG_SET_DEFAULT(CompilationPolicyChoice, 3);
  }
  ......
}
# hotspot/src/share/vm/runtime/compilationPolicy.cpp
// Determine compilation policy based on command line argument
void compilationPolicy_init() {
  CompilationPolicy::set_in_vm_startup(DelayCompilationDuringStartup);
  switch(CompilationPolicyChoice) {
  ......
  case 3:
#ifdef TIERED
    CompilationPolicy::set_policy(new AdvancedThresholdPolicy());
#else
    Unimplemented();
#endif
    break;
  ......
  CompilationPolicy::policy()->initialize();
}

# hotspot/src/share/vm/runtime/advancedThresholdPolicy.cpp
void AdvancedThresholdPolicy::initialize() {
  // Turn on ergonomic compiler count selection
  if (FLAG_IS_DEFAULT(CICompilerCountPerCPU) && FLAG_IS_DEFAULT(CICompilerCount)) {
    FLAG_SET_DEFAULT(CICompilerCountPerCPU, true);
  }
  int count = CICompilerCount;
  if (CICompilerCountPerCPU) {
    // Simple log n seems to grow too slowly for tiered, try something faster: log n * log log n
    int log_cpu = log2_int(os::active_processor_count());
    int loglog_cpu = log2_int(MAX2(log_cpu, 1));
    count = MAX2(log_cpu * loglog_cpu, 1) * 3 / 2;
  }
  set_c1_count(MAX2(count / 3, 1));
  set_c2_count(MAX2(count - c1_count(), 1));
  ......
}

jinfo -flag CICompilerCount 
-XX:CICompilerCount=18

# ByteBuffer.java
    public static ByteBuffer allocateDirect(int capacity) {
        return new DirectByteBuffer(capacity);
    }
# DirectByteBuffer.java
  DirectByteBuffer(int cap) {                   // package-private
        ......
        long base = 0;
        try {
            base = unsafe.allocateMemory(size);
        }
       ......
# Unsafe.java
  public native long allocateMemory(long bytes);
# hotspot/src/share/vm/prims/unsafe.cpp
UNSAFE_ENTRY(jlong, Unsafe_AllocateMemory(JNIEnv *env, jobject unsafe, jlong size))
  UnsafeWrapper("Unsafe_AllocateMemory");
  size_t sz = (size_t)size;
  ......
  sz = round_to(sz, HeapWordSize);
  void* x = os::malloc(sz, mtInternal);
  ......
UNSAFE_END

import java.nio.ByteBuffer;
public class ByteBufferTest {
    private static int _1M = 1024 * 1024;
    private static ByteBuffer allocateBuffer_1 = ByteBuffer.allocateDirect(128 * _1M);
    private static ByteBuffer allocateBuffer_2 = ByteBuffer.allocateDirect(256 * _1M);
    public static void main(String[] args) throws Exception {
        System.out.println("MaxDirect memory: " + sun.misc.VM.maxDirectMemory() + " bytes");
        System.out.println("Direct allocation: " + (allocateBuffer_1.capacity() + allocateBuffer_2.capacity()) + " bytes");
        System.out.println("Native memory used: " + sun.misc.SharedSecrets.getJavaNioAccess().getDirectBufferPool().getMemoryUsed() + " bytes");
        Thread.sleep(6000000);
    }
}

-                  Internal (reserved=405202KB, committed=405202KB)
                            (malloc=405170KB #3605) 
                            (mmap: reserved=32KB, committed=32KB) 
                   ......
                   [0x0000ffffbb599190] Unsafe_AllocateMemory+0x1c0
                   [0x0000ffffa40157a8]
                             (malloc=393216KB type=Internal #2)
                   ......
                   [0x0000ffffbb04b3f8] GenericGrowableArray::raw_allocate(int)+0x188
                   [0x0000ffffbb4339d8] PerfDataManager::add_item(PerfData*, bool) [clone .constprop.16]+0x108
                   [0x0000ffffbb434118] PerfDataManager::create_string_variable(CounterNS, char const*, int, char const*, Thread*)+0x178
                   [0x0000ffffbae9d400] CompilerCounters::CompilerCounters(char const*, int, Thread*) [clone .part.78]+0xb0
                             (malloc=3KB type=Internal #1)
                   ......

public class StringTableTest {
    public static void main(String[] args) throws Exception {
        while (true){
            String str = new String("StringTestData_" + System.currentTimeMillis());
            str.intern();
        }
    }
}

Total: reserved=2831553KB +20095KB, committed=1515457KB +20095KB
......
-                    Symbol (reserved=18991KB +17144KB, committed=18991KB +17144KB)
                            (malloc=18504KB +17144KB #2307 +2143)
                            (arena=488KB #1)
......
[0x0000ffffa2aef4a8] BasicHashtable<(MemoryType)9>::new_entry(unsigned int)+0x1a0
[0x0000ffffa2aef558] Hashtable::new_entry(unsigned int, oopDesc*)+0x28
[0x0000ffffa2fbff78] StringTable::basic_add(int, Handle, unsigned short*, int, unsigned int, Thread*)+0xe0
[0x0000ffffa2fc0548] StringTable::intern(Handle, unsigned short*, int, Thread*)+0x1a0
                             (malloc=17592KB type=Symbol +17144KB #2199 +2143)
......

-                    Symbol (reserved=100859KB +17416KB, committed=100859KB +17416KB)
                            (malloc=100371KB +17416KB #2359 +2177)
                            (arena=488KB #1)
......
[0x0000ffffa30c14a8] BasicHashtable<(MemoryType)9>::new_entry(unsigned int)+0x1a0
[0x0000ffffa30c1558] Hashtable::new_entry(unsigned int, oopDesc*)+0x28
[0x0000ffffa3591f78] StringTable::basic_add(int, Handle, unsigned short*, int, unsigned int, Thread*)+0xe0
[0x0000ffffa3592548] StringTable::intern(Handle, unsigned short*, int, Thread*)+0x1a0
                             (malloc=18008KB type=Symbol +17416KB #2251 +2177)

# hotsopt/src/share/vm/classfile/symnolTable.hpp
  StringTable() : RehashableHashtable((int)StringTableSize,
                              sizeof (HashtableEntry)) {}
  StringTable(HashtableBucket* t, int number_of_entries)
    : RehashableHashtable((int)StringTableSize, sizeof (HashtableEntry), t,
                     number_of_entries) {}

StringTable statistics:
Number of buckets       :  16777216 = 134217728 bytes, each 8
Number of entries       :     39703 =    635248 bytes, each 16
Number of literals      :     39703 =   2849304 bytes, avg  71.765
Total footprsize_t         :           = 137702280 bytes
Average bucket size     :     0.002
Variance of bucket size :     0.002
Std. dev. of bucket size:     0.049
Maximum bucket size     :         2
SymbolTable statistics:
Number of buckets       :     20011 =    160088 bytes, each 8
Number of entries       :     20133 =    483192 bytes, each 24
Number of literals      :     20133 =    753832 bytes, avg  37.443
Total footprint         :           =   1397112 bytes
Average bucket size     :     1.006
Variance of bucket size :     1.013
Std. dev. of bucket size:     1.006
Maximum bucket size     :         9

# /hotspot/src/share/vm/services/memTracker.cpp
void MemTracker::init() {
  NMT_TrackingLevel level = tracking_level();
  ......
}
# /hotspot/src/share/vm/services/memTracker.hpp
static inline NMT_TrackingLevel tracking_level() {
    if (_tracking_level == NMT_unknown) {
      // No fencing is needed here, since JVM is in single-threaded
      // mode.
      _tracking_level = init_tracking_level();
      _cmdline_tracking_level = _tracking_level;
    }
    return _tracking_level;
  }
# /hotspot/src/share/vm/services/memTracker.cpp
NMT_TrackingLevel MemTracker::init_tracking_level() {
  NMT_TrackingLevel level = NMT_off;
  ......
  if (os::getenv(buf, nmt_option, sizeof(nmt_option))) {
    if (strcmp(nmt_option, "summary") == 0) {
      level = NMT_summary;
    } else if (strcmp(nmt_option, "detail") == 0) {
#if PLATFORM_NATIVE_STACK_WALKING_SUPPORTED
      level = NMT_detail;
#else
      level = NMT_summary;
#endif // PLATFORM_NATIVE_STACK_WALKING_SUPPORTED
    } 
   ......
  }
  ......
  if (!MallocTracker::initialize(level) ||
      !VirtualMemoryTracker::initialize(level)) {
    level = NMT_off;
  }
  return level;
}
# /hotspot/src/share/vm/services/memTracker.cpp
bool MallocTracker::initialize(NMT_TrackingLevel level) {
  if (level >= NMT_summary) {
    MallocMemorySummary::initialize();
  }
  if (level == NMT_detail) {
    return MallocSiteTable::initialize();
  }
  return true;
}
void MallocMemorySummary::initialize() {
  assert(sizeof(_snapshot) >= sizeof(MallocMemorySnapshot), "Sanity Check");
  // Uses placement new operator to initialize static area.
  ::new ((void*)_snapshot)MallocMemorySnapshot();
}
# 
bool VirtualMemoryTracker::initialize(NMT_TrackingLevel level) {
  if (level >= NMT_summary) {
    VirtualMemorySummary::initialize();
  }
  return true;
}

[0x0000ffff935906e0] ChunkPool::allocate(unsigned long, AllocFailStrategy::AllocFailEnum)+0x158
[0x0000ffff9358ec14] Arena::Arena(MemoryType, unsigned long)+0x18c
......

# /hotspot/src/share/vm/runtime/thread.cpp
Thread::Thread() {
  ......
  set_resource_area(new (mtThread)ResourceArea());
  ......
  set_handle_area(new (mtThread) HandleArea(NULL));
  ......

develop(bool, UseMallocOnly, false,                                       \
          "Use only malloc/free for allocation (no resource area/arena)") 

# hotspot/src/share/vm/memory/allocation.hpp
void* Amalloc(size_t x, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM) {
    assert(is_power_of_2(ARENA_AMALLOC_ALIGNMENT) , "should be a power of 2");
    x = ARENA_ALIGN(x);
    //debug 版本限制
    debug_only(if (UseMallocOnly) return malloc(x);)
    if (!check_for_overflow(x, "Arena::Amalloc", alloc_failmode))
      return NULL;
    NOT_PRODUCT(inc_bytes_allocated(x);)
    if (_hwm + x > _max) {
      return grow(x, alloc_failmode);
    } else {
      char *old = _hwm;
      _hwm += x;
      return old;
    }
  }

# 正常 JVM ，啟動(dòng)參數(shù)添加：-XX:+IgnoreUnrecognizedVMOptions -XX:+UseMallocOnly
......
[0x0000ffffb7d16968] ChunkPool::allocate(unsigned long, AllocFailStrategy::AllocFailEnum)+0x158
[0x0000ffffb7d15f58] Arena::grow(unsigned long, AllocFailStrategy::AllocFailEnum)+0x50
[0x0000ffffb7fc4888] Dict::Dict(int (*)(void const*, void const*), int (*)(void const*), Arena*, int)+0x138
[0x0000ffffb85e5968] Type::Initialize_shared(Compile*)+0xb0
                             (malloc=32KB type=Arena Chunk #1)
......                             
# debug版本 JVM ，啟動(dòng)參數(shù)添加：-XX:+UseMallocOnly
......
[0x0000ffff8dfae910] Arena::malloc(unsigned long)+0x74
[0x0000ffff8e2cb3b8] Arena::Amalloc_4(unsigned long, AllocFailStrategy::AllocFailEnum)+0x70
[0x0000ffff8e2c9d5c] Dict::Dict(int (*)(void const*, void const*), int (*)(void const*), Arena*, int)+0x19c
[0x0000ffff8e97c3d0] Type::Initialize_shared(Compile*)+0x9c
                             (malloc=5KB type=Arena Chunk #1)
......                             

# hotspot/src/share/vm/memory/allocation.cpp
void* Arena::malloc(size_t size) {
  assert(UseMallocOnly, "shouldn't call");
  // use malloc, but save pointer in res. area for later freeing
  char** save = (char**)internal_malloc_4(sizeof(char*));
  return (*save = (char*)os::malloc(size, mtChunk));
}

# hotspot/src/share/vm/memory/allocation.cpp
// debugging code
inline void Arena::free_all(char** start, char** end) {
  for (char** p = start; p < end; p++) if (*p) os::free(*p);
}