rosalloc.cc

namespace art {
namespace gc {
namespace allocator {


extern "C" void* art_heap_rosalloc_morecore(RosAlloc* rosalloc, intptr_t increment);


static constexpr bool kUsePrefetchDuringAllocRun = true;
static constexpr bool kPrefetchNewRunDataByZeroing = false;
static constexpr size_t kPrefetchStride = 64;


size_t RosAlloc::bracketSizes[kNumOfSizeBrackets];
size_t RosAlloc::numOfPages[kNumOfSizeBrackets];
size_t RosAlloc::numOfSlots[kNumOfSizeBrackets];
size_t RosAlloc::headerSizes[kNumOfSizeBrackets];
size_t RosAlloc::bulkFreeBitMapOffsets[kNumOfSizeBrackets];
size_t RosAlloc::threadLocalFreeBitMapOffsets[kNumOfSizeBrackets];
bool RosAlloc::initialized_ = false;
size_t RosAlloc::dedicated_full_run_storage_[kPageSize / sizeof(size_t)] = { 0 };
RosAlloc::Run* RosAlloc::dedicated_full_run_ =
    reinterpret_cast<RosAlloc::Run*>(dedicated_full_run_storage_);


RosAlloc::RosAlloc(void* base, size_t capacity, size_t max_capacity,
                   PageReleaseMode page_release_mode, size_t page_release_size_threshold)
    : base_(reinterpret_cast<byte*>(base)), footprint_(capacity),
      capacity_(capacity), max_capacity_(max_capacity),
      lock_("rosalloc global lock", kRosAllocGlobalLock),
      bulk_free_lock_("rosalloc bulk free lock", kRosAllocBulkFreeLock),
      page_release_mode_(page_release_mode),
      page_release_size_threshold_(page_release_size_threshold) {
  DCHECK_EQ(RoundUp(capacity, kPageSize), capacity);
  DCHECK_EQ(RoundUp(max_capacity, kPageSize), max_capacity);
  CHECK_LE(capacity, max_capacity);
  CHECK(IsAligned<kPageSize>(page_release_size_threshold_));
  if (!initialized_) {
  // 初始化偏移等信息
    Initialize();
  }
  VLOG(heap) << "RosAlloc base="
             << std::hex << (intptr_t)base_ << ", end="
             << std::hex << (intptr_t)(base_ + capacity_)
             << ", capacity=" << std::dec << capacity_
             << ", max_capacity=" << std::dec << max_capacity_;
  for (size_t i = 0; i < kNumOfSizeBrackets; i++) {
    size_bracket_lock_names_[i] =
        StringPrintf("an rosalloc size bracket %d lock", static_cast<int>(i));
    size_bracket_locks_[i] = new Mutex(size_bracket_lock_names_[i].c_str(), kRosAllocBracketLock);
    current_runs_[i] = dedicated_full_run_;
  }
  DCHECK_EQ(footprint_, capacity_);
  size_t num_of_pages = footprint_ / kPageSize;
  size_t max_num_of_pages = max_capacity_ / kPageSize;
  std::string error_msg;
  page_map_mem_map_.reset(MemMap::MapAnonymous("rosalloc page map", NULL, RoundUp(max_num_of_pages, kPageSize),
                                               PROT_READ | PROT_WRITE, false, &error_msg));
  CHECK(page_map_mem_map_.get() != nullptr) << "Couldn't allocate the page map : " << error_msg;
  // 这段mmap来的区域实际是做监视内存用
  page_map_ = page_map_mem_map_->Begin();
  page_map_size_ = num_of_pages;
  max_page_map_size_ = max_num_of_pages;
  free_page_run_size_map_.resize(num_of_pages);
  // fpr的基地址是在rosalloc创建的时候传进来的，也是rosalloc space创建的时候的参数
  FreePageRun* free_pages = reinterpret_cast<FreePageRun*>(base_);
  if (kIsDebugBuild) {
    free_pages->magic_num_ = kMagicNumFree;
  }
  free_pages->SetByteSize(this, capacity_);
  DCHECK_EQ(capacity_ % kPageSize, static_cast<size_t>(0));
  DCHECK(free_pages->IsFree());
  free_pages->ReleasePages(this);
  DCHECK(free_pages->IsFree());
  free_page_runs_.insert(free_pages);
  if (kTraceRosAlloc) {
    LOG(INFO) << "RosAlloc::RosAlloc() : Inserted run 0x" << std::hex
              << reinterpret_cast<intptr_t>(free_pages)
              << " into free_page_runs_";
  }
}


RosAlloc::~RosAlloc() {
  for (size_t i = 0; i < kNumOfSizeBrackets; i++) {
    delete size_bracket_locks_[i];
  }
}


// alloc large object 或者 alloc run的时候可能调到
void* RosAlloc::AllocPages(Thread* self, size_t num_pages, byte page_map_type) {
  lock_.AssertHeld(self);
  DCHECK(page_map_type == kPageMapRun || page_map_type == kPageMapLargeObject);
  FreePageRun* res = NULL;
  const size_t req_byte_size = num_pages * kPageSize;
  // Find the lowest address free page run that's large enough.
  for (auto it = free_page_runs_.begin(); it != free_page_runs_.end(); ) {
    FreePageRun* fpr = *it;
    DCHECK(fpr->IsFree());
    size_t fpr_byte_size = fpr->ByteSize(this);
    DCHECK_EQ(fpr_byte_size % kPageSize, static_cast<size_t>(0));
    if (req_byte_size <= fpr_byte_size) {
      // Found one.
      free_page_runs_.erase(it++);
      if (kTraceRosAlloc) {
        LOG(INFO) << "RosAlloc::AllocPages() : Erased run 0x"
                  << std::hex << reinterpret_cast<intptr_t>(fpr)
                  << " from free_page_runs_";
      }
 // 切割
      if (req_byte_size < fpr_byte_size) {
        // Split.
        FreePageRun* remainder = reinterpret_cast<FreePageRun*>(reinterpret_cast<byte*>(fpr) + req_byte_size);
        if (kIsDebugBuild) {
          remainder->magic_num_ = kMagicNumFree;
        }
        remainder->SetByteSize(this, fpr_byte_size - req_byte_size);
        DCHECK_EQ(remainder->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        // Don't need to call madvise on remainder here.
        // 多余的插入fpr
        free_page_runs_.insert(remainder);
        if (kTraceRosAlloc) {
          LOG(INFO) << "RosAlloc::AllocPages() : Inserted run 0x" << std::hex
                    << reinterpret_cast<intptr_t>(remainder)
                    << " into free_page_runs_";
        }
        fpr->SetByteSize(this, req_byte_size);
        DCHECK_EQ(fpr->ByteSize(this) % kPageSize, static_cast<size_t>(0));
      }
      res = fpr;
      break;
    } else {
      ++it;
    }
  }


  // Failed to allocate pages. Grow the footprint, if possible.
  //　分配失败
  if (UNLIKELY(res == NULL && capacity_ > footprint_)) {
    FreePageRun* last_free_page_run = NULL;
    size_t last_free_page_run_size;
// 返回最后一个元素的反向迭代器
    auto it = free_page_runs_.rbegin();
// rosalloc末尾有无fpr
    if (it != free_page_runs_.rend() && (last_free_page_run = *it)->End(this) == base_ + footprint_) {
      // There is a free page run at the end.
      DCHECK(last_free_page_run->IsFree());
      DCHECK(IsFreePage(ToPageMapIndex(last_free_page_run)));
 // 得到最后一个fpr的大小
      last_free_page_run_size = last_free_page_run->ByteSize(this);
    } else {
      // There is no free page run at the end.
      last_free_page_run_size = 0;
    }
    DCHECK_LT(last_free_page_run_size, req_byte_size);
// 如果增长率空间，能否满足要求
    if (capacity_ - footprint_ + last_free_page_run_size >= req_byte_size) {
      // If we grow the heap, we can allocate it.
      // 最低能增长两兆
      size_t increment = std::min(std::max(2 * MB, req_byte_size - last_free_page_run_size),
                                  capacity_ - footprint_);
      DCHECK_EQ(increment % kPageSize, static_cast<size_t>(0));
      size_t new_footprint = footprint_ + increment;
      size_t new_num_of_pages = new_footprint / kPageSize;
      DCHECK_LT(page_map_size_, new_num_of_pages);
      DCHECK_LT(free_page_run_size_map_.size(), new_num_of_pages);
      page_map_size_ = new_num_of_pages;
      DCHECK_LE(page_map_size_, max_page_map_size_);
      free_page_run_size_map_.resize(new_num_of_pages);
      art_heap_rosalloc_morecore(this, increment);
      if (last_free_page_run_size > 0) {
        // There was a free page run at the end. Expand its size.
        DCHECK_EQ(last_free_page_run_size, last_free_page_run->ByteSize(this));
// 如果末尾有fpr就扩张，如果没有重做一个fpr
        last_free_page_run->SetByteSize(this, last_free_page_run_size + increment);
        DCHECK_EQ(last_free_page_run->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        DCHECK_EQ(last_free_page_run->End(this), base_ + new_footprint);
      } else {
        // Otherwise, insert a new free page run at the end.
        FreePageRun* new_free_page_run = reinterpret_cast<FreePageRun*>(base_ + footprint_);
        if (kIsDebugBuild) {
          new_free_page_run->magic_num_ = kMagicNumFree;
        }
        new_free_page_run->SetByteSize(this, increment);
        DCHECK_EQ(new_free_page_run->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        free_page_runs_.insert(new_free_page_run);
        DCHECK_EQ(*free_page_runs_.rbegin(), new_free_page_run);
        if (kTraceRosAlloc) {
          LOG(INFO) << "RosAlloc::AlloPages() : Grew the heap by inserting run 0x"
                    << std::hex << reinterpret_cast<intptr_t>(new_free_page_run)
                    << " into free_page_runs_";
        }
      }
      DCHECK_LE(footprint_ + increment, capacity_);
      if (kTraceRosAlloc) {
        LOG(INFO) << "RosAlloc::AllocPages() : increased the footprint from "
                  << footprint_ << " to " << new_footprint;
      }
      footprint_ = new_footprint;


      // And retry the last free page run.
      // 重来一次
      it = free_page_runs_.rbegin();
      DCHECK(it != free_page_runs_.rend());
      FreePageRun* fpr = *it;
      if (kIsDebugBuild && last_free_page_run_size > 0) {
        DCHECK(last_free_page_run != NULL);
        DCHECK_EQ(last_free_page_run, fpr);
      }
      size_t fpr_byte_size = fpr->ByteSize(this);
      DCHECK_EQ(fpr_byte_size % kPageSize, static_cast<size_t>(0));
      DCHECK_LE(req_byte_size, fpr_byte_size);
      free_page_runs_.erase(fpr);
      if (kTraceRosAlloc) {
        LOG(INFO) << "RosAlloc::AllocPages() : Erased run 0x" << std::hex << reinterpret_cast<intptr_t>(fpr)
                  << " from free_page_runs_";
      }
 // 分割
      if (req_byte_size < fpr_byte_size) {
        // Split if there's a remainder.
        FreePageRun* remainder = reinterpret_cast<FreePageRun*>(reinterpret_cast<byte*>(fpr) + req_byte_size);
        if (kIsDebugBuild) {
          remainder->magic_num_ = kMagicNumFree;
        }
        remainder->SetByteSize(this, fpr_byte_size - req_byte_size);
        DCHECK_EQ(remainder->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        free_page_runs_.insert(remainder);
        if (kTraceRosAlloc) {
          LOG(INFO) << "RosAlloc::AllocPages() : Inserted run 0x" << std::hex
                    << reinterpret_cast<intptr_t>(remainder)
                    << " into free_page_runs_";
        }
        fpr->SetByteSize(this, req_byte_size);
        DCHECK_EQ(fpr->ByteSize(this) % kPageSize, static_cast<size_t>(0));
      }
      res = fpr;
    }
  }
  if (LIKELY(res != NULL)) {
    // Update the page map.
    // 更新目前正在使用的page map
    size_t page_map_idx = ToPageMapIndex(res);
    for (size_t i = 0; i < num_pages; i++) {
      DCHECK(IsFreePage(page_map_idx + i));
    }
    switch (page_map_type) {
    case kPageMapRun:
      page_map_[page_map_idx] = kPageMapRun;
      for (size_t i = 1; i < num_pages; i++) {
        page_map_[page_map_idx + i] = kPageMapRunPart;
      }
      break;
    case kPageMapLargeObject:
      page_map_[page_map_idx] = kPageMapLargeObject;
      for (size_t i = 1; i < num_pages; i++) {
        page_map_[page_map_idx + i] = kPageMapLargeObjectPart;
      }
      break;
    default:
      LOG(FATAL) << "Unreachable - page map type: " << page_map_type;
      break;
    }
    if (kIsDebugBuild) {
      // Clear the first page since it is not madvised due to the magic number.
      memset(res, 0, kPageSize);
    }
    if (kTraceRosAlloc) {
      LOG(INFO) << "RosAlloc::AllocPages() : 0x" << std::hex << reinterpret_cast<intptr_t>(res)
                << "-0x" << (reinterpret_cast<intptr_t>(res) + num_pages * kPageSize)
                << "(" << std::dec << (num_pages * kPageSize) << ")";
    }
    return res;
  }


  // Fail.
  if (kTraceRosAlloc) {
    LOG(INFO) << "RosAlloc::AllocPages() : NULL";
  }
  return nullptr;
}


// 释放页面
size_t RosAlloc::FreePages(Thread* self, void* ptr, bool already_zero) {
  lock_.AssertHeld(self);
  size_t pm_idx = ToPageMapIndex(ptr);
  DCHECK_LT(pm_idx, page_map_size_);
  // 根据page_idx找到page_type
  byte pm_type = page_map_[pm_idx];
  DCHECK(pm_type == kPageMapRun || pm_type == kPageMapLargeObject);
  byte pm_part_type;
  switch (pm_type) {
  case kPageMapRun:
    pm_part_type = kPageMapRunPart;
    break;
  case kPageMapLargeObject:
    pm_part_type = kPageMapLargeObjectPart;
    break;
  default:
    LOG(FATAL) << "Unreachable - " << __PRETTY_FUNCTION__ << " : " << "pm_idx=" << pm_idx << ", pm_type="
               << static_cast<int>(pm_type) << ", ptr=" << std::hex
               << reinterpret_cast<intptr_t>(ptr);
    return 0;
  }
  // Update the page map and count the number of pages.
  size_t num_pages = 1;
  page_map_[pm_idx] = kPageMapEmpty;
  size_t idx = pm_idx + 1;
  size_t end = page_map_size_;
  // 标记位empty
  while (idx < end && page_map_[idx] == pm_part_type) {
    page_map_[idx] = kPageMapEmpty;
    num_pages++;
    idx++;
  }
  const size_t byte_size = num_pages * kPageSize;
  if (already_zero) {
    if (kCheckZeroMemory) {
      const uword* word_ptr = reinterpret_cast<uword*>(ptr);
      for (size_t i = 0; i < byte_size / sizeof(uword); ++i) {
        CHECK_EQ(word_ptr[i], 0U) << "words don't match at index " << i;
      }
    }
  } else if (!DoesReleaseAllPages()) {
    memset(ptr, 0, byte_size);
  }


  if (kTraceRosAlloc) {
    LOG(INFO) << __PRETTY_FUNCTION__ << " : 0x" << std::hex << reinterpret_cast<intptr_t>(ptr)
              << "-0x" << (reinterpret_cast<intptr_t>(ptr) + byte_size)
              << "(" << std::dec << (num_pages * kPageSize) << ")";
  }


  // Turn it into a free run.
  // 作为一个新的ptr
  FreePageRun* fpr = reinterpret_cast<FreePageRun*>(ptr);
  if (kIsDebugBuild) {
    fpr->magic_num_ = kMagicNumFree;
  }
  fpr->SetByteSize(this, byte_size);
  DCHECK(IsAligned<kPageSize>(fpr->ByteSize(this)));


  DCHECK(free_page_runs_.find(fpr) == free_page_runs_.end());
  if (!free_page_runs_.empty()) {
    // Try to coalesce in the higher address direction.
    if (kTraceRosAlloc) {
      LOG(INFO) << __PRETTY_FUNCTION__ << "RosAlloc::FreePages() : trying to coalesce a free page run 0x"
                << std::hex << reinterpret_cast<uintptr_t>(fpr) << " [" << std::dec << pm_idx << "] -0x"
                << std::hex << reinterpret_cast<uintptr_t>(fpr->End(this)) << " [" << std::dec
                << (fpr->End(this) == End() ? page_map_size_ : ToPageMapIndex(fpr->End(this))) << "]";
    }
    auto higher_it = free_page_runs_.upper_bound(fpr);
// 尝试向下合并
    if (higher_it != free_page_runs_.end()) {
      for (auto it = higher_it; it != free_page_runs_.end(); ) {
        FreePageRun* h = *it;
        DCHECK_EQ(h->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        if (kTraceRosAlloc) {
          LOG(INFO) << "RosAlloc::FreePages() : trying to coalesce with a higher free page run 0x"
                    << std::hex << reinterpret_cast<uintptr_t>(h) << " [" << std::dec << ToPageMapIndex(h) << "] -0x"
                    << std::hex << reinterpret_cast<uintptr_t>(h->End(this)) << " [" << std::dec
                    << (h->End(this) == End() ? page_map_size_ : ToPageMapIndex(h->End(this))) << "]";
        }
        if (fpr->End(this) == h->Begin()) {
          if (kTraceRosAlloc) {
            LOG(INFO) << "Success";
          }
          // Clear magic num since this is no longer the start of a free page run.
          if (kIsDebugBuild) {
            h->magic_num_ = 0;
          }
          free_page_runs_.erase(it++);
          if (kTraceRosAlloc) {
            LOG(INFO) << "RosAlloc::FreePages() : (coalesce) Erased run 0x" << std::hex
                      << reinterpret_cast<intptr_t>(h)
                      << " from free_page_runs_";
          }
          fpr->SetByteSize(this, fpr->ByteSize(this) + h->ByteSize(this));
          DCHECK_EQ(fpr->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        } else {
          // Not adjacent. Stop.
          if (kTraceRosAlloc) {
            LOG(INFO) << "Fail";
          }
          break;
        }
      }
    }
    // Try to coalesce in the lower address direction.
    // 向上合并(低地址)
    auto lower_it = free_page_runs_.upper_bound(fpr);
    if (lower_it != free_page_runs_.begin()) {
      --lower_it;
      for (auto it = lower_it; ; ) {
        // We want to try to coalesce with the first element but
        // there's no "<=" operator for the iterator.
        bool to_exit_loop = it == free_page_runs_.begin();


        FreePageRun* l = *it;
        DCHECK_EQ(l->ByteSize(this) % kPageSize, static_cast<size_t>(0));
        if (kTraceRosAlloc) {
          LOG(INFO) << "RosAlloc::FreePages() : trying to coalesce with a lower free page run 0x"
                    << std::hex << reinterpret_cast<uintptr_t>(l) << " [" << std::dec << ToPageMapIndex(l) << "] -0x"
                    << std::hex << reinterpret_cast<uintptr_t>(l->End(this)) << " [" << std::dec
                    << (l->End(this) == End() ? page_map_size_ : ToPageMapIndex(l->End(this))) << "]";
        }
        if (l->End(this) == fpr->Begin()) {
          if (kTraceRosAlloc) {
            LOG(INFO) << "Success";
          }
          free_page_runs_.erase(it--);
          if (kTraceRosAlloc) {
            LOG(INFO) << "RosAlloc::FreePages() : (coalesce) Erased run 0x" << std::hex
                      << reinterpret_cast<intptr_t>(l)
                      << " from free_page_runs_";
          }
          l->SetByteSize(this, l->ByteSize(this) + fpr->ByteSize(this));
          DCHECK_EQ(l->ByteSize(this) % kPageSize, static_cast<size_t>(0));
          // Clear magic num since this is no longer the start of a free page run.
          if (kIsDebugBuild) {
            fpr->magic_num_ = 0;
          }
          fpr = l;
        } else {
          // Not adjacent. Stop.
          if (kTraceRosAlloc) {
            LOG(INFO) << "Fail";
          }
          break;
        }
        if (to_exit_loop) {
          break;
        }
      }
    }
  }


  // Insert it.
  DCHECK_EQ(fpr->ByteSize(this) % kPageSize, static_cast<size_t>(0));
  DCHECK(free_page_runs_.find(fpr) == free_page_runs_.end());
  DCHECK(fpr->IsFree());
  fpr->ReleasePages(this);
  DCHECK(fpr->IsFree());
  free_page_runs_.insert(fpr);
  DCHECK(free_page_runs_.find(fpr) != free_page_runs_.end());
  if (kTraceRosAlloc) {
    LOG(INFO) << "RosAlloc::FreePages() : Inserted run 0x" << std::hex << reinterpret_cast<intptr_t>(fpr)
              << " into free_page_runs_";
  }
  return byte_size;
}


// 分配大对象，通过alloc page
void* RosAlloc::AllocLargeObject(Thread* self, size_t size, size_t* bytes_allocated) {
  DCHECK_GT(size, kLargeSizeThreshold);
  size_t num_pages = RoundUp(size, kPageSize) / kPageSize;
  void* r;
  {
    MutexLock mu(self, lock_);
    r = AllocPages(self, num_pages, kPageMapLargeObject);
  }
  if (UNLIKELY(r == nullptr)) {
    if (kTraceRosAlloc) {
      LOG(INFO) << "RosAlloc::AllocLargeObject() : NULL";
    }
    return nullptr;
  }
  const size_t total_bytes = num_pages * kPageSize;
  *bytes_allocated = total_bytes;
  if (kTraceRosAlloc) {
    LOG(INFO) << "RosAlloc::AllocLargeObject() : 0x" << std::hex << reinterpret_cast<intptr_t>(r)
              << "-0x" << (reinterpret_cast<intptr_t>(r) + num_pages * kPageSize)
              << "(" << std::dec << (num_pages * kPageSize) << ")";
  }
  // Check if the returned memory is really all zero.
  if (kCheckZeroMemory) {
    CHECK_EQ(total_bytes % sizeof(uword), 0U);
    const uword* words = reinterpret_cast<uword*>(r);
    for (size_t i = 0; i < total_bytes / sizeof(uword); ++i) {
      CHECK_EQ(words[i], 0U);
    }
  }
  return r;
}


// 释放
size_t RosAlloc::FreeInternal(Thread* self, void* ptr) {
  DCHECK_LE(base_, ptr);
  DCHECK_LT(ptr, base_ + footprint_);
  size_t pm_idx = RoundDownToPageMapIndex(ptr);
  Run* run = nullptr;
  {
    MutexLock mu(self, lock_);
    DCHECK_LT(pm_idx, page_map_size_);
    byte page_map_entry = page_map_[pm_idx];
    if (kTraceRosAlloc) {
      LOG(INFO) << "RosAlloc::FreeInternal() : " << std::hex << ptr << ", pm_idx=" << std::dec << pm_idx
                << ", page_map_entry=" << static_cast<int>(page_map_entry);
    }
    switch (page_map_[pm_idx]) {
      case kPageMapLargeObject:
  // free从fpr中分配的内存
        return FreePages(self, ptr, false);
      case kPageMapLargeObjectPart:
        LOG(FATAL) << "Unreachable - page map type: " << page_map_[pm_idx];
        return 0;
      case kPageMapRunPart: {
        // Find the beginning of the run.
        do {
          --pm_idx;
          DCHECK_LT(pm_idx, capacity_ / kPageSize);
        } while (page_map_[pm_idx] != kPageMapRun);
        // Fall-through.
      case kPageMapRun:
        run = reinterpret_cast<Run*>(base_ + pm_idx * kPageSize);
        DCHECK_EQ(run->magic_num_, kMagicNum);
        break;
      case kPageMapReleased:
        // Fall-through.
      case kPageMapEmpty:
        LOG(FATAL) << "Unreachable - page map type: " << page_map_[pm_idx];
        return 0;
      }
      default:
        LOG(FATAL) << "Unreachable - page map type: " << page_map_[pm_idx];
        return 0;
    }
  }
  DCHECK(run != nullptr);
  // free run中分配的内存
  return FreeFromRun(self, ptr, run);
}


size_t RosAlloc::Free(Thread* self, void* ptr) {
  ReaderMutexLock rmu(self, bulk_free_lock_);
  return FreeInternal(self, ptr);
}


// 分配run
RosAlloc::Run* RosAlloc::AllocRun(Thread* self, size_t idx) {
  RosAlloc::Run* new_run = nullptr;
  {
    MutexLock mu(self, lock_);
// 在fpr中分配page用于分配run
    new_run = reinterpret_cast<Run*>(AllocPages(self, numOfPages[idx], kPageMapRun));
  }
  if (LIKELY(new_run != nullptr)) {
    if (kIsDebugBuild) {
      new_run->magic_num_ = kMagicNum;
    }
    new_run->size_bracket_idx_ = idx;
// 标记无效位
    new_run->SetAllocBitMapBitsForInvalidSlots();
    DCHECK(!new_run->IsThreadLocal());
    DCHECK_EQ(new_run->first_search_vec_idx_, 0U);
    DCHECK(!new_run->to_be_bulk_freed_);
    if (kUsePrefetchDuringAllocRun && idx < kNumThreadLocalSizeBrackets) {
      // Take ownership of the cache lines if we are likely to be thread local run.
      if (kPrefetchNewRunDataByZeroing) {
        // Zeroing the data is sometimes faster than prefetching but it increases memory usage
        // since we end up dirtying zero pages which may have been madvised.
        new_run->ZeroData();
      } else {
        const size_t num_of_slots = numOfSlots[idx];
        const size_t bracket_size = bracketSizes[idx];
        const size_t num_of_bytes = num_of_slots * bracket_size;
        byte* begin = reinterpret_cast<byte*>(new_run) + headerSizes[idx];
        for (size_t i = 0; i < num_of_bytes; i += kPrefetchStride) {
          __builtin_prefetch(begin + i);
        }
      }
    }
  }
  return new_run;
}


// 从二分树获得不满的run进行填满操作
RosAlloc::Run* RosAlloc::RefillRun(Thread* self, size_t idx) {
  // Get the lowest address non-full run from the binary tree.
  std::set<Run*>* const bt = &non_full_runs_[idx];
  if (!bt->empty()) {
    // If there's one, use it as the current run.
    auto it = bt->begin();
    Run* non_full_run = *it;
    DCHECK(non_full_run != nullptr);
    DCHECK(!non_full_run->IsThreadLocal());
    bt->erase(it);
    return non_full_run;
  }
  // If there's none, allocate a new run and use it as the current run.
  return AllocRun(self, idx);
}


inline void* RosAlloc::AllocFromCurrentRunUnlocked(Thread* self, size_t idx) {
  Run* current_run = current_runs_[idx];
  DCHECK(current_run != nullptr);
  void* slot_addr = current_run->AllocSlot();
  // 如果没有分配到
  if (UNLIKELY(slot_addr == nullptr)) {
    // The current run got full. Try to refill it.
    DCHECK(current_run->IsFull());
    if (kIsDebugBuild && current_run != dedicated_full_run_) {
      full_runs_[idx].insert(current_run);
      if (kTraceRosAlloc) {
        LOG(INFO) << __PRETTY_FUNCTION__ << " : Inserted run 0x" << std::hex
                  << reinterpret_cast<intptr_t>(current_run)
                  << " into full_runs_[" << std::dec << idx << "]";
      }
      DCHECK(non_full_runs_[idx].find(current_run) == non_full_runs_[idx].end());
      DCHECK(full_runs_[idx].find(current_run) != full_runs_[idx].end());
    }
// 重新获取新的run
    current_run = RefillRun(self, idx);
    if (UNLIKELY(current_run == nullptr)) {
      // Failed to allocate a new run, make sure that it is the dedicated full run.
      current_runs_[idx] = dedicated_full_run_;
      return nullptr;
    }
    DCHECK(current_run != nullptr);
    DCHECK(non_full_runs_[idx].find(current_run) == non_full_runs_[idx].end());
    DCHECK(full_runs_[idx].find(current_run) == full_runs_[idx].end());
    current_run->SetIsThreadLocal(false);
    current_runs_[idx] = current_run;
    DCHECK(!current_run->IsFull());
    slot_addr = current_run->AllocSlot();
    // Must succeed now with a new run.
    DCHECK(slot_addr != nullptr);
  }
  return slot_addr;
}


// 非线程安全，非tl
void* RosAlloc::AllocFromRunThreadUnsafe(Thread* self, size_t size, size_t* bytes_allocated) {
  DCHECK_LE(size, kLargeSizeThreshold);
  size_t bracket_size;
  size_t idx = SizeToIndexAndBracketSize(size, &bracket_size);
  DCHECK_EQ(idx, SizeToIndex(size));
  DCHECK_EQ(bracket_size, IndexToBracketSize(idx));
  DCHECK_EQ(bracket_size, bracketSizes[idx]);
  DCHECK_LE(size, bracket_size);
  DCHECK(size > 512 || bracket_size - size < 16);
  Locks::mutator_lock_->AssertExclusiveHeld(self);
  // 从当前current中分配内存
  void* slot_addr = AllocFromCurrentRunUnlocked(self, idx);
  if (LIKELY(slot_addr != nullptr)) {
    DCHECK(bytes_allocated != nullptr);
    *bytes_allocated = bracket_size;
    // Caller verifies that it is all 0.
  }
  return slot_addr;
}


// 从thread local中分配
// 所有内存都是在建立rosalloc之前已经mmap(猜测?)
// 什么时候分配给current?
void* RosAlloc::AllocFromRun(Thread* self, size_t size, size_t* bytes_allocated) {
  DCHECK_LE(size, kLargeSizeThreshold);
  size_t bracket_size;
  // 找到大小框的idx
  size_t idx = SizeToIndexAndBracketSize(size, &bracket_size);
  DCHECK_EQ(idx, SizeToIndex(size));
  DCHECK_EQ(bracket_size, IndexToBracketSize(idx));
  DCHECK_EQ(bracket_size, bracketSizes[idx]);
  DCHECK_LE(size, bracket_size);
  DCHECK(size > 512 || bracket_size - size < 16);


  void* slot_addr;


  if (LIKELY(idx < kNumThreadLocalSizeBrackets)) {
    // Use a thread-local run.
    // 使用tl run
    Run* thread_local_run = reinterpret_cast<Run*>(self->GetRosAllocRun(idx));
    // Allow invalid since this will always fail the allocation.
    if (kIsDebugBuild) {
      // Need the lock to prevent race conditions.
      MutexLock mu(self, *size_bracket_locks_[idx]);
      CHECK(non_full_runs_[idx].find(thread_local_run) == non_full_runs_[idx].end());
      CHECK(full_runs_[idx].find(thread_local_run) == full_runs_[idx].end());
    }
    DCHECK(thread_local_run != nullptr);
    DCHECK(thread_local_run->IsThreadLocal() || thread_local_run == dedicated_full_run_);
// 根据alloc bitmap分配
slot_addr = thread_local_run->AllocSlot();
    // The allocation must fail if the run is invalid.
    DCHECK(thread_local_run != dedicated_full_run_ || slot_addr == nullptr)
        << "allocated from an invalid run";
// 分配失败(说明没有free了?)
    if (UNLIKELY(slot_addr == nullptr)) {
      // The run got full. Try to free slots.
      DCHECK(thread_local_run->IsFull());
      MutexLock mu(self, *size_bracket_locks_[idx]);
      bool is_all_free_after_merge;
      // This is safe to do for the dedicated_full_run_ since the bitmaps are empty.
      // tl bitmap上全为0，即全为free
      if (thread_local_run->MergeThreadLocalFreeBitMapToAllocBitMap(&is_all_free_after_merge)) {
        DCHECK_NE(thread_local_run, dedicated_full_run_);
        // Some slot got freed. Keep it.
        DCHECK(!thread_local_run->IsFull());
        DCHECK_EQ(is_all_free_after_merge, thread_local_run->IsAllFree());
        if (is_all_free_after_merge) {
          // Check that the bitmap idx is back at 0 if it's all free.
          DCHECK_EQ(thread_local_run->first_search_vec_idx_, 0U);
        }
      } else {
        // No slots got freed. Try to refill the thread-local run.
        DCHECK(thread_local_run->IsFull());
        if (thread_local_run != dedicated_full_run_) {
          thread_local_run->SetIsThreadLocal(false);
          if (kIsDebugBuild) {
            full_runs_[idx].insert(thread_local_run);
            if (kTraceRosAlloc) {
              LOG(INFO) << "RosAlloc::AllocFromRun() : Inserted run 0x" << std::hex
                        << reinterpret_cast<intptr_t>(thread_local_run)
                        << " into full_runs_[" << std::dec << idx << "]";
            }
          }
          DCHECK(non_full_runs_[idx].find(thread_local_run) == non_full_runs_[idx].end());
          DCHECK(full_runs_[idx].find(thread_local_run) != full_runs_[idx].end());
        }


        thread_local_run = RefillRun(self, idx);
        if (UNLIKELY(thread_local_run == nullptr)) {
          self->SetRosAllocRun(idx, dedicated_full_run_);
          return nullptr;
        }
        DCHECK(non_full_runs_[idx].find(thread_local_run) == non_full_runs_[idx].end());
        DCHECK(full_runs_[idx].find(thread_local_run) == full_runs_[idx].end());
        thread_local_run->SetIsThreadLocal(true);
        self->SetRosAllocRun(idx, thread_local_run);
        DCHECK(!thread_local_run->IsFull());
      }


      DCHECK(thread_local_run != nullptr);
      DCHECK(!thread_local_run->IsFull());
      DCHECK(thread_local_run->IsThreadLocal());
      slot_addr = thread_local_run->AllocSlot();
      // Must succeed now with a new run.
      DCHECK(slot_addr != nullptr);
    }
    if (kTraceRosAlloc) {
      LOG(INFO) << "RosAlloc::AllocFromRun() thread-local : 0x" << std::hex << reinterpret_cast<intptr_t>(slot_addr)
                << "-0x" << (reinterpret_cast<intptr_t>(slot_addr) + bracket_size)
                << "(" << std::dec << (bracket_size) << ")";
    }
  } else {
    // Use the (shared) current run.
    MutexLock mu(self, *size_bracket_locks_[idx]);
    slot_addr = AllocFromCurrentRunUnlocked(self, idx);
    if (kTraceRosAlloc) {
      LOG(INFO) << "RosAlloc::AllocFromRun() : 0x" << std::hex << reinterpret_cast<intptr_t>(slot_addr)
                << "-0x" << (reinterpret_cast<intptr_t>(slot_addr) + bracket_size)
                << "(" << std::dec << (bracket_size) << ")";
    }
  }
  DCHECK(bytes_allocated != nullptr);
  *bytes_allocated = bracket_size;
  // Caller verifies that it is all 0.
  return slot_addr;
}




std::string RosAlloc::Run::Dump() {
  size_t idx = size_bracket_idx_;
  size_t num_slots = numOfSlots[idx];
  size_t num_vec = RoundUp(num_slots, 32) / 32;
  std::ostringstream stream;
  stream << "RosAlloc Run = " << reinterpret_cast<void*>(this)
         << "{ magic_num=" << static_cast<int>(magic_num_)
         << " size_bracket_idx=" << idx
         << " is_thread_local=" << static_cast<int>(is_thread_local_)
         << " to_be_bulk_freed=" << static_cast<int>(to_be_bulk_freed_)
         << " first_search_vec_idx=" << first_search_vec_idx_
         << " alloc_bit_map=" << BitMapToStr(alloc_bit_map_, num_vec)
         << " bulk_free_bit_map=" << BitMapToStr(BulkFreeBitMap(), num_vec)
         << " thread_local_bit_map=" << BitMapToStr(ThreadLocalFreeBitMap(), num_vec)
         << " }" << std::endl;
  return stream.str();
}


inline void* RosAlloc::Run::AllocSlot() {
  const size_t idx = size_bracket_idx_;
  while (true) {
    if (kIsDebugBuild) {
      // Make sure that no slots leaked, the bitmap should be full for all previous vectors.
      for (size_t i = 0; i < first_search_vec_idx_; ++i) {
        CHECK_EQ(~alloc_bit_map_[i], 0U);
      }
    }
// 由于alloc bitmap很多，所以用数组表示
    uint32_t* const alloc_bitmap_ptr = &alloc_bit_map_[first_search_vec_idx_];
// 举例 1000000010000 ffzl为5
// 第一次标记全为1，分配失败。已分配的被标记为1
    uint32_t ffz1 = __builtin_ffs(~*alloc_bitmap_ptr);
    if (LIKELY(ffz1 != 0)) {
      const uint32_t ffz = ffz1 - 1;
 // 找到slot下标，kBitsPerByte一个字节8位
      const uint32_t slot_idx = ffz + first_search_vec_idx_ * sizeof(*alloc_bitmap_ptr) * kBitsPerByte;
      const uint32_t mask = 1U << ffz;
      DCHECK_LT(slot_idx, numOfSlots[idx]) << "out of range";
      // Found an empty slot. Set the bit.
      DCHECK_EQ(*alloc_bitmap_ptr & mask, 0U);
 // bitmap清零
      *alloc_bitmap_ptr |= mask;
      DCHECK_NE(*alloc_bitmap_ptr & mask, 0U);
 // run基地址 + 头大小 + 槽位idx * 对应slot大小(分箱大小)
      byte* slot_addr = reinterpret_cast<byte*>(this) + headerSizes[idx] + slot_idx * bracketSizes[idx];
      if (kTraceRosAlloc) {
        LOG(INFO) << "RosAlloc::Run::AllocSlot() : 0x" << std::hex << reinterpret_cast<intptr_t>(slot_addr)
                  << ", bracket_size=" << std::dec << bracketSizes[idx] << ", slot_idx=" << slot_idx;
      }
      return slot_addr;
    }
    const size_t num_words = RoundUp(numOfSlots[idx], 32) / 32;
    if (first_search_vec_idx_ + 1 >= num_words) {
      DCHECK(IsFull());
      // Already at the last word, return null.
      return nullptr;
    }
    // Increase the index to the next word and try again.
    ++first_search_vec_idx_;
  }
}


// 主要步骤
// 1、清标记位  2、清内存
void RosAlloc::Run::FreeSlot(void* ptr) {
  DCHECK(!IsThreadLocal());
  const byte idx = size_bracket_idx_;
  const size_t bracket_size = bracketSizes[idx];
  // 算出slot的偏移
  const size_t offset_from_slot_base = reinterpret_cast<byte*>(ptr)
      - (reinterpret_cast<byte*>(this) + headerSizes[idx]);
  DCHECK_EQ(offset_from_slot_base % bracket_size, static_cast<size_t>(0));
  size_t slot_idx = offset_from_slot_base / bracket_size;
  DCHECK_LT(slot_idx, numOfSlots[idx]);
  size_t vec_idx = slot_idx / 32;
  if (kIsDebugBuild) {
    size_t num_vec = RoundUp(numOfSlots[idx], 32) / 32;
    DCHECK_LT(vec_idx, num_vec);
  }
  size_t vec_off = slot_idx % 32;
  uint32_t* vec = &alloc_bit_map_[vec_idx];
  first_search_vec_idx_ = std::min(first_search_vec_idx_, static_cast<uint32_t>(vec_idx));
  const uint32_t mask = 1U << vec_off;
  DCHECK_NE(*vec & mask, 0U);
  *vec &= ~mask;
  DCHECK_EQ(*vec & mask, 0U);
  // Zero out the memory.
  // TODO: Investigate alternate memset since ptr is guaranteed to be aligned to 16.
  memset(ptr, 0, bracket_size);
  if (kTraceRosAlloc) {
    LOG(INFO) << "RosAlloc::Run::FreeSlot() : 0x" << std::hex << reinterpret_cast<intptr_t>(ptr)
              << ", bracket_size=" << std::dec << bracketSizes[idx] << ", slot_idx=" << slot_idx;
  }
}


// thread local与Rosalloc mem的关系
// 返回tl bitmap之前是不是0
inline bool RosAlloc::Run::MergeThreadLocalFreeBitMapToAllocBitMap(bool* is_all_free_after_out) {
  DCHECK(IsThreadLocal());
  // Free slots in the alloc bit map based on the thread local free bit map.
  const size_t idx = size_bracket_idx_;
  // 每个run所包含的slot的个数
  const size_t num_of_slots = numOfSlots[idx];
  const size_t num_vec = RoundUp(num_of_slots, 32) / 32;
  bool changed = false;
  // alloc bitmap
  uint32_t* vecp = &alloc_bit_map_[0];
  // tl alloc bitmap
  uint32_t* tl_free_vecp = &ThreadLocalFreeBitMap()[0];
  bool is_all_free_after = true;
  for (size_t v = 0; v < num_vec; v++, vecp++, tl_free_vecp++) {
    uint32_t tl_free_vec = *tl_free_vecp;
    uint32_t vec_before = *vecp;
    uint32_t vec_after;
// tl非0，则合并到vec_before，vec发生改变，changed为true
    if (tl_free_vec != 0) {
      first_search_vec_idx_ = std::min(first_search_vec_idx_, static_cast<uint32_t>(v));
      vec_after = vec_before & ~tl_free_vec;
      *vecp = vec_after;
      changed = true;
      *tl_free_vecp = 0;  // clear the thread local free bit map.
    } else {
      vec_after = vec_before;
    }
// 合并之后有slot被使用了
    if (vec_after != 0) {
// 如果vec_after之后不为0，说明并非全是free
      if (v == num_vec - 1) {
  // 已经合并到最后一个，由于最后一个前面含有无效slot的标记，因此需要另外判断。
        // Only not all free if a bit other than the mask bits are set.
        is_all_free_after =
            is_all_free_after && GetBitmapLastVectorMask(num_of_slots, num_vec) == vec_after;
      } else {
        is_all_free_after = false;
      }
    }
    DCHECK_EQ(*tl_free_vecp, static_cast<uint32_t>(0));
  }
  *is_all_free_after_out = is_all_free_after;
  // Return true if there was at least a bit set in the thread-local
  // free bit map and at least a bit in the alloc bit map changed.
  return changed;
}


inline void RosAlloc::Run::SetAllocBitMapBitsForInvalidSlots() {
  const size_t idx = size_bracket_idx_;
  const size_t num_slots = numOfSlots[idx];
  const size_t num_vec = RoundUp(num_slots, 32) / 32;
  DCHECK_NE(num_vec, 0U);
  // Make sure to set the bits at the end of the bitmap so that we don't allocate there since they
  // don't represent valid slots.
  // 空余slot的bitmap位填1，填于高位
  alloc_bit_map_[num_vec - 1] |= GetBitmapLastVectorMask(num_slots, num_vec);
}


//初始化header置0
inline void RosAlloc::Run::ZeroHeader() {
  const byte idx = size_bracket_idx_;
  memset(this, 0, headerSizes[idx]);
}


//初始化data置0
inline void RosAlloc::Run::ZeroData() {
  const byte idx = size_bracket_idx_;
  byte* slot_begin = reinterpret_cast<byte*>(this) + headerSizes[idx];
  memset(slot_begin, 0, numOfSlots[idx] * bracketSizes[idx]);
}


// rosalloc 初始化
void RosAlloc::Initialize() {
  // bracketSizes.
  // kNumOfSizeBrackets = 34
  for (size_t i = 0; i < kNumOfSizeBrackets; i++) {
    if (i < kNumOfSizeBrackets - 2) {
      bracketSizes[i] = 16 * (i + 1);
    } else if (i == kNumOfSizeBrackets - 2) {
      bracketSizes[i] = 1 * KB;
    } else {
      DCHECK_EQ(i, kNumOfSizeBrackets - 1);
      bracketSizes[i] = 2 * KB;
    }
    if (kTraceRosAlloc) {
      LOG(INFO) << "bracketSizes[" << i << "]=" << bracketSizes[i];
    }
  }
  // numOfPages.
  // 每个bracket可用于被分配的page大小
  for (size_t i = 0; i < kNumOfSizeBrackets; i++) {
    if (i < 4) {
      numOfPages[i] = 1;
    } else if (i < 8) {
      numOfPages[i] = 2;
    } else if (i < 16) {
      numOfPages[i] = 4;
    } else if (i < 32) {
      numOfPages[i] = 8;
    } else if (i == 32) {
      DCHECK_EQ(i, kNumOfSizeBrackets - 2);
      numOfPages[i] = 16;
    } else {
      DCHECK_EQ(i, kNumOfSizeBrackets - 1);
      numOfPages[i] = 32;
    }
    if (kTraceRosAlloc) {
      LOG(INFO) << "numOfPages[" << i << "]=" << numOfPages[i];
    }
  }
  // Compute numOfSlots and slotOffsets.
  for (size_t i = 0; i < kNumOfSizeBrackets; i++) {
    size_t bracket_size = bracketSizes[i];
    size_t run_size = kPageSize * numOfPages[i];
// 计算slots个数
    size_t max_num_of_slots = run_size / bracket_size;
    // Compute the actual number of slots by taking the header and
    // alignment into account.
    // 固定头大小
    size_t fixed_header_size = RoundUp(Run::fixed_header_size(), sizeof(uint32_t));
    DCHECK_EQ(fixed_header_size, static_cast<size_t>(8));
    size_t header_size = 0;
    size_t bulk_free_bit_map_offset = 0;
    size_t thread_local_free_bit_map_offset = 0;
    size_t num_of_slots = 0;
    // Search for the maximum number of slots that allows enough space
    // for the header (including the bit maps.)
    // 由于run结尾应用了一个0长度数组，该处为寻找合适的head和body的分界点
    for (int s = max_num_of_slots; s >= 0; s--) {
// slot所占大小
      size_t tmp_slots_size = bracket_size * s;
// s向上对齐为sizeof(uint32_t) * kBitsPerByte
      size_t tmp_bit_map_size = RoundUp(s, sizeof(uint32_t) * kBitsPerByte) / kBitsPerByte;
      size_t tmp_bulk_free_bit_map_size = tmp_bit_map_size;
      size_t tmp_bulk_free_bit_map_off = fixed_header_size + tmp_bit_map_size;
      size_t tmp_thread_local_free_bit_map_size = tmp_bit_map_size;
 
 // 一个run的构成
 // alloc_bit_map 某个slot被分配出去就在alloc_bit_map上标记出来
 //fixed header size + alloc_bit_map + bulk_free_bit_map(tmp_bit_map_size) 
 // + thread_local_free_bit_map(tmp_bit_map_size)
      size_t tmp_thread_local_free_bit_map_off = tmp_bulk_free_bit_map_off + tmp_bulk_free_bit_map_size;
      size_t tmp_unaligned_header_size = tmp_thread_local_free_bit_map_off + tmp_thread_local_free_bit_map_size;
      // Align up the unaligned header size. bracket_size may not be a power of two.
      // 凑成bracket_size的整数倍，对齐
      size_t tmp_header_size = (tmp_unaligned_header_size % bracket_size == 0) ?
          tmp_unaligned_header_size :
          tmp_unaligned_header_size + (bracket_size - tmp_unaligned_header_size % bracket_size);
      DCHECK_EQ(tmp_header_size % bracket_size, static_cast<size_t>(0));
      DCHECK_EQ(tmp_header_size % 8, static_cast<size_t>(0));
      if (tmp_slots_size + tmp_header_size <= run_size) {
        // Found the right number of slots, that is, there was enough
        // space for the header (including the bit maps.)
        num_of_slots = s;
        header_size = tmp_header_size;
        bulk_free_bit_map_offset = tmp_bulk_free_bit_map_off;
        thread_local_free_bit_map_offset = tmp_thread_local_free_bit_map_off;
        break;
      }
    }
    DCHECK(num_of_slots > 0 && header_size > 0 && bulk_free_bit_map_offset > 0);
    // Add the padding for the alignment remainder.
    // slot与head直接的间隙
    header_size += run_size % bracket_size;
    DCHECK_EQ(header_size + num_of_slots * bracket_size, run_size);
    numOfSlots[i] = num_of_slots;
    headerSizes[i] = header_size;
    bulkFreeBitMapOffsets[i] = bulk_free_bit_map_offset;
    threadLocalFreeBitMapOffsets[i] = thread_local_free_bit_map_offset;
    if (kTraceRosAlloc) {
      LOG(INFO) << "numOfSlots[" << i << "]=" << numOfSlots[i]
                << ", headerSizes[" << i << "]=" << headerSizes[i]
                << ", bulkFreeBitMapOffsets[" << i << "]=" << bulkFreeBitMapOffsets[i]
                << ", threadLocalFreeBitMapOffsets[" << i << "]=" << threadLocalFreeBitMapOffsets[i];;
    }
  }
  // Fill the alloc bitmap so nobody can successfully allocate from it.
  if (kIsDebugBuild) {
    dedicated_full_run_->magic_num_ = kMagicNum;
  }
  
  // It doesn't matter which size bracket we use since the main goal is to have the allocation
  // fail 100% of the time you attempt to allocate into the dedicated full run.
  // 牺牲run目前只做初始化，只有分配过程100%失败，才尝试在牺牲run分配
  // 该run只是作为一个占位符?
  dedicated_full_run_->size_bracket_idx_ = 0;
  dedicated_full_run_->FillAllocBitMap();
  dedicated_full_run_->SetIsThreadLocal(true);
}




}  // namespace allocator
}  // namespace gc
}  // namespace art