openjdk17 jvm堆空间分配

##堆空间分配源码

jint Universe::initialize_heap() {
  assert(_collectedHeap == NULL, "Heap already created");
  _collectedHeap = GCConfig::arguments()->create_heap();

  log_info(gc)("Using %s", _collectedHeap->name());
  return _collectedHeap->initialize();
}

##

jint G1CollectedHeap::initialize() {

  // Necessary to satisfy locking discipline assertions.

  MutexLocker x(Heap_lock);

  // While there are no constraints in the GC code that HeapWordSize
  // be any particular value, there are multiple other areas in the
  // system which believe this to be true (e.g. oop->object_size in some
  // cases incorrectly returns the size in wordSize units rather than
  // HeapWordSize).
  guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");

  size_t init_byte_size = InitialHeapSize;
  size_t reserved_byte_size = G1Arguments::heap_reserved_size_bytes();

  // Ensure that the sizes are properly aligned.
  Universe::check_alignment(init_byte_size, HeapRegion::GrainBytes, "g1 heap");
  Universe::check_alignment(reserved_byte_size, HeapRegion::GrainBytes, "g1 heap");
  Universe::check_alignment(reserved_byte_size, HeapAlignment, "g1 heap");

  // Reserve the maximum.

  // When compressed oops are enabled, the preferred heap base
  // is calculated by subtracting the requested size from the
  // 32Gb boundary and using the result as the base address for
  // heap reservation. If the requested size is not aligned to
  // HeapRegion::GrainBytes (i.e. the alignment that is passed
  // into the ReservedHeapSpace constructor) then the actual
  // base of the reserved heap may end up differing from the
  // address that was requested (i.e. the preferred heap base).
  // If this happens then we could end up using a non-optimal
  // compressed oops mode.

  ReservedHeapSpace heap_rs = Universe::reserve_heap(reserved_byte_size,
                                                     HeapAlignment);

  initialize_reserved_region(heap_rs);

  // Create the barrier set for the entire reserved region.
  G1CardTable* ct = new G1CardTable(heap_rs.region());
  ct->initialize();
  G1BarrierSet* bs = new G1BarrierSet(ct);
  bs->initialize();
  assert(bs->is_a(BarrierSet::G1BarrierSet), "sanity");
  BarrierSet::set_barrier_set(bs);
  _card_table = ct;

  {
    G1SATBMarkQueueSet& satbqs = bs->satb_mark_queue_set();
    satbqs.set_process_completed_buffers_threshold(G1SATBProcessCompletedThreshold);
    satbqs.set_buffer_enqueue_threshold_percentage(G1SATBBufferEnqueueingThresholdPercent);
  }

  // Create the hot card cache.
  _hot_card_cache = new G1HotCardCache(this);

  // Create space mappers.
  size_t page_size = heap_rs.page_size();
  G1RegionToSpaceMapper* heap_storage =
    G1RegionToSpaceMapper::create_mapper(heap_rs,
                                         heap_rs.size(),
                                         page_size,
                                         HeapRegion::GrainBytes,
                                         1,
                                         mtJavaHeap);
  if(heap_storage == NULL) {
    vm_shutdown_during_initialization("Could not initialize G1 heap");
    return JNI_ERR;
  }

  os::trace_page_sizes("Heap",
                       MinHeapSize,
                       reserved_byte_size,
                       page_size,
                       heap_rs.base(),
                       heap_rs.size());
  heap_storage->set_mapping_changed_listener(&_listener);

  // Create storage for the BOT, card table, card counts table (hot card cache) and the bitmaps.
  G1RegionToSpaceMapper* bot_storage =
    create_aux_memory_mapper("Block Offset Table",
                             G1BlockOffsetTable::compute_size(heap_rs.size() / HeapWordSize),
                             G1BlockOffsetTable::heap_map_factor());

  G1RegionToSpaceMapper* cardtable_storage =
    create_aux_memory_mapper("Card Table",
                             G1CardTable::compute_size(heap_rs.size() / HeapWordSize),
                             G1CardTable::heap_map_factor());

  G1RegionToSpaceMapper* card_counts_storage =
    create_aux_memory_mapper("Card Counts Table",
                             G1CardCounts::compute_size(heap_rs.size() / HeapWordSize),
                             G1CardCounts::heap_map_factor());

  size_t bitmap_size = G1CMBitMap::compute_size(heap_rs.size());
  G1RegionToSpaceMapper* prev_bitmap_storage =
    create_aux_memory_mapper("Prev Bitmap", bitmap_size, G1CMBitMap::heap_map_factor());
  G1RegionToSpaceMapper* next_bitmap_storage =
    create_aux_memory_mapper("Next Bitmap", bitmap_size, G1CMBitMap::heap_map_factor());

  _hrm.initialize(heap_storage, prev_bitmap_storage, next_bitmap_storage, bot_storage, cardtable_storage, card_counts_storage);
  _card_table->initialize(cardtable_storage);

  // Do later initialization work for concurrent refinement.
  _hot_card_cache->initialize(card_counts_storage);

  // 6843694 - ensure that the maximum region index can fit
  // in the remembered set structures.
  const uint max_region_idx = (1U << (sizeof(RegionIdx_t)*BitsPerByte-1)) - 1;
  guarantee((max_reserved_regions() - 1) <= max_region_idx, "too many regions");

  // The G1FromCardCache reserves card with value 0 as "invalid", so the heap must not
  // start within the first card.
  guarantee(heap_rs.base() >= (char*)G1CardTable::card_size, "Java heap must not start within the first card.");
  G1FromCardCache::initialize(max_reserved_regions());
  // Also create a G1 rem set.
  _rem_set = new G1RemSet(this, _card_table, _hot_card_cache);
  _rem_set->initialize(max_reserved_regions());

  size_t max_cards_per_region = ((size_t)1 << (sizeof(CardIdx_t)*BitsPerByte-1)) - 1;
  guarantee(HeapRegion::CardsPerRegion > 0, "make sure it's initialized");
  guarantee(HeapRegion::CardsPerRegion < max_cards_per_region,
            "too many cards per region");

  FreeRegionList::set_unrealistically_long_length(max_regions() + 1);

  _bot = new G1BlockOffsetTable(reserved(), bot_storage);

  {
    size_t granularity = HeapRegion::GrainBytes;

    _region_attr.initialize(reserved(), granularity);
    _humongous_reclaim_candidates.initialize(reserved(), granularity);
  }

  _workers = new WorkGang("GC Thread", ParallelGCThreads,
                          true /* are_GC_task_threads */,
                          false /* are_ConcurrentGC_threads */);
  if (_workers == NULL) {
    return JNI_ENOMEM;
  }
  _workers->initialize_workers();

  _numa->set_region_info(HeapRegion::GrainBytes, page_size);

  // Create the G1ConcurrentMark data structure and thread.
  // (Must do this late, so that "max_[reserved_]regions" is defined.)
  _cm = new G1ConcurrentMark(this, prev_bitmap_storage, next_bitmap_storage);
  _cm_thread = _cm->cm_thread();

  // Now expand into the initial heap size.
  if (!expand(init_byte_size, _workers)) {
    vm_shutdown_during_initialization("Failed to allocate initial heap.");
    return JNI_ENOMEM;
  }

  // Perform any initialization actions delegated to the policy.
  policy()->init(this, &_collection_set);

  jint ecode = initialize_concurrent_refinement();
  if (ecode != JNI_OK) {
    return ecode;
  }

  ecode = initialize_service_thread();
  if (ecode != JNI_OK) {
    return ecode;
  }

  // Initialize and schedule sampling task on service thread.
  _rem_set->initialize_sampling_task(service_thread());

  // Create and schedule the periodic gc task on the service thread.
  _periodic_gc_task = new G1PeriodicGCTask("Periodic GC Task");
  _service_thread->register_task(_periodic_gc_task);

  {
    G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
    dcqs.set_process_cards_threshold(concurrent_refine()->yellow_zone());
    dcqs.set_max_cards(concurrent_refine()->red_zone());
  }

  // Here we allocate the dummy HeapRegion that is required by the
  // G1AllocRegion class.
  HeapRegion* dummy_region = _hrm.get_dummy_region();

  // We'll re-use the same region whether the alloc region will
  // require BOT updates or not and, if it doesn't, then a non-young
  // region will complain that it cannot support allocations without
  // BOT updates. So we'll tag the dummy region as eden to avoid that.
  dummy_region->set_eden();
  // Make sure it's full.
  dummy_region->set_top(dummy_region->end());
  G1AllocRegion::setup(this, dummy_region);

  _allocator->init_mutator_alloc_regions();

  // Do create of the monitoring and management support so that
  // values in the heap have been properly initialized.
  _g1mm = new G1MonitoringSupport(this);

  _preserved_marks_set.init(ParallelGCThreads);

  _collection_set.initialize(max_reserved_regions());

  _regions_failed_evacuation = NEW_C_HEAP_ARRAY(volatile bool, max_regions(), mtGC);

  G1InitLogger::print();

  return JNI_OK;
}

##

ReservedHeapSpace Universe::reserve_heap(size_t heap_size, size_t alignment) {

  assert(alignment <= Arguments::conservative_max_heap_alignment(),
         "actual alignment " SIZE_FORMAT " must be within maximum heap alignment " SIZE_FORMAT,
         alignment, Arguments::conservative_max_heap_alignment());

  size_t total_reserved = align_up(heap_size, alignment);
  assert(!UseCompressedOops || (total_reserved <= (OopEncodingHeapMax - os::vm_page_size())),
      "heap size is too big for compressed oops");

  size_t page_size = os::vm_page_size();
  if (UseLargePages && is_aligned(alignment, os::large_page_size())) {
    page_size = os::large_page_size();
  } else {
    // Parallel is the only collector that might opt out of using large pages
    // for the heap.
    assert(!UseLargePages || UseParallelGC , "Wrong alignment to use large pages");
  }

  // Now create the space.
  ReservedHeapSpace total_rs(total_reserved, alignment, page_size, AllocateHeapAt);

  if (total_rs.is_reserved()) {
    assert((total_reserved == total_rs.size()) && ((uintptr_t)total_rs.base() % alignment == 0),
           "must be exactly of required size and alignment");
    // We are good.

    if (AllocateHeapAt != NULL) {
      log_info(gc,heap)("Successfully allocated Java heap at location %s", AllocateHeapAt);
    }

    if (UseCompressedOops) {
      CompressedOops::initialize(total_rs);
    }

    Universe::calculate_verify_data((HeapWord*)total_rs.base(), (HeapWord*)total_rs.end());

    return total_rs;
  }

  vm_exit_during_initialization(
    err_msg("Could not reserve enough space for " SIZE_FORMAT "KB object heap",
            total_reserved/K));

  // satisfy compiler
  ShouldNotReachHere();
  return ReservedHeapSpace(0, 0, os::vm_page_size());
}

##

bool G1CollectedHeap::expand(size_t expand_bytes, WorkGang* pretouch_workers, double* expand_time_ms) {
  size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
  aligned_expand_bytes = align_up(aligned_expand_bytes,
                                       HeapRegion::GrainBytes);

  log_debug(gc, ergo, heap)("Expand the heap. requested expansion amount: " SIZE_FORMAT "B expansion amount: " SIZE_FORMAT "B",
                            expand_bytes, aligned_expand_bytes);

  if (is_maximal_no_gc()) {
    log_debug(gc, ergo, heap)("Did not expand the heap (heap already fully expanded)");
    return false;
  }

  double expand_heap_start_time_sec = os::elapsedTime();
  uint regions_to_expand = (uint)(aligned_expand_bytes / HeapRegion::GrainBytes);
  assert(regions_to_expand > 0, "Must expand by at least one region");

  uint expanded_by = _hrm.expand_by(regions_to_expand, pretouch_workers);
  if (expand_time_ms != NULL) {
    *expand_time_ms = (os::elapsedTime() - expand_heap_start_time_sec) * MILLIUNITS;
  }

  if (expanded_by > 0) {
    size_t actual_expand_bytes = expanded_by * HeapRegion::GrainBytes;
    assert(actual_expand_bytes <= aligned_expand_bytes, "post-condition");
    policy()->record_new_heap_size(num_regions());
  } else {
    log_debug(gc, ergo, heap)("Did not expand the heap (heap expansion operation failed)");

    // The expansion of the virtual storage space was unsuccessful.
    // Let's see if it was because we ran out of swap.
    if (G1ExitOnExpansionFailure &&
        _hrm.available() >= regions_to_expand) {
      // We had head room...
      vm_exit_out_of_memory(aligned_expand_bytes, OOM_MMAP_ERROR, "G1 heap expansion");
    }
  }
  return regions_to_expand > 0;
}