art 的 Space

 

static constexpr space::LargeObjectSpaceType kDefaultLargeObjectSpaceType =USE_ART_LOW_4G_ALLOCATOR ?space::LargeObjectSpaceType::kFreeList: space::LargeObjectSpaceType::kMap;

heap 初始化的时候large_object_space_type 取值由kDefaultLargeObjectSpaceType 决定，__aarch64__ 架构 USE_ART_LOW_4G_ALLOCATOR为true，取 kFreeList type。

1.Bump PointerSpace

Bump PointerSpace：
提供的内存分配方式是顺序分配，每次新申请的都是上次分配的对象的尾地址紧挨着分配，释放内存都是用AllocSpace的clear方法

1（12kb）

2（8kb）

3（8kb）

free

free

2.LargeObjectSpace

LargeObjectSpace：
（1）heap 初始化的时候large_object_space_type 取值由kDefaultLargeObjectSpaceType 决定，__aarch64__ 架构 USE_ART_LOW_4G_ALLOCATOR为true，取 kFreeList type。

#if defined(__LP64__) && !defined(__Fuchsia__) && \     (defined(__aarch64__) || defined(__mips__) || defined(__APPLE__)) #define USE_ART_LOW_4G_ALLOCATOR 1 static constexpr space::LargeObjectSpaceType kDefaultLargeObjectSpaceType = USE_ART_LOW_4G_ALLOCATOR ? space::LargeObjectSpaceType::kFreeList : space::LargeObjectSpaceType::kMap;

 

（2）根据large_object_space_type的区别再去决定创建的子类，FreeListSpace或者LargeObjectMapSpace ，

if (large_object_space_type == space::LargeObjectSpaceType::kFreeList) {    large_object_space_ = space::FreeListSpace::Create("free list large object space", capacity_);    CHECK(large_object_space_ != nullptr) << "Failed to create large object space";  } else if (large_object_space_type == space::LargeObjectSpaceType::kMap) {    large_object_space_ = space::LargeObjectMapSpace::Create("mem map large object space");    CHECK(large_object_space_ != nullptr) << "Failed to create large object space";  }

 

（3）我们是aarch64架构的，会初始化 FreeListSpace ，creat 函数如两个参，一个是名字，第二个是空间大小，这个是由 dalvik.vm.heapsize 配置的，我们系统配置512M

capacity_ 取值 MemoryMaximumSize  ，这就是parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");设置的，默认是16M，我们系统设置[dalvik.vm.heapsize]: [512m] 创建mem_map 对象，具体的内存分配就是在这块进行的。 MemMap mem_map = MemMap::MapAnonymous(name.c_str(),                                         size,                                         PROT_READ | PROT_WRITE,                                         /*low_4gb=*/ true,                                         &error_msg); 然后根据创建的mem_map以及它的基地址和结束地址创建FreeListSpace对象 new FreeListSpace(name, std::move(mem_map), mem_map.Begin(), mem_map.End());

3.regionSpcae

Regionspace

regionspace会把内存划分区域（region 大小是256kb）去管理，一些重要的对象：

//region 的内存大小 static constexpr size_t kRegionSize = 256 * KB;   //regions_作为保存域的数组 std::unique_ptr<Region[]> regions_ GUARDED_BY(region_lock_);   num_regions_ space中region的数量 num_non_free_regions_ 使用的region数量 max_peak_num_non_free_regions_ non_free_region_index_limit_ current_region_ evac_region_ cyclic_alloc_region_index_     GC相关的对象 //从spce创建开始，GC回收的次数。 uint32_t time_    //是否分代，由Heap::use_generational_cc_决定 const bool use_generational_cc_;   //GC的时候被标记的内存对应的bitmap ，Mark bitmap used by the GC. std::unique_ptr<accounting::ContinuousSpaceBitmap> mark_bitmap_;   // The number of evac regions allocated during collection. 0 when GC not running. size_t num_evac_regions_ GUARDED_BY(region_lock_);   // Maintain the maximum of number of non-free regions collected just before // reclaim in each GC cycle. At this moment in cycle, highest number of // regions are in non-free. size_t max_peak_num_non_free_regions_;

 

Region

enum class RegionType : uint8_t {   kRegionTypeAll,              // All types.   kRegionTypeFromSpace,        // From-space. To be evacuated.   kRegionTypeUnevacFromSpace,  // Unevacuated from-space. Not to be evacuated.   kRegionTypeToSpace,          // To-space.   kRegionTypeNone,             // None. };   enum class RegionState : uint8_t {   kRegionStateFree,            // Free region.   kRegionStateAllocated,       // Allocated region.   kRegionStateLarge,           // Large allocated (allocation larger than the region size).   kRegionStateLargeTail,       // Large tail (non-first regions of a large allocation). };       Region()       : idx_(static_cast<size_t>(-1)),         live_bytes_(static_cast<size_t>(-1)),         begin_(nullptr),         thread_(nullptr),         top_(nullptr),         end_(nullptr),         objects_allocated_(0),         alloc_time_(0),         is_newly_allocated_(false),         is_a_tlab_(false),         state_(RegionState::kRegionStateAllocated),         type_(RegionType::kRegionTypeToSpace) {}

4.ZygoteSpace

ZygoteSpace： ZygoteSpace* ZygoteSpace::Create(const std::string& name,                                  MemMap&& mem_map,                                  accounting::ContinuousSpaceBitmap* live_bitmap,                                  accounting::ContinuousSpaceBitmap* mark_bitmap) { name live_bitmap mark_bitmap 计算mem_map这块内存中的对象个数   CountObjectsAllocated visitor(&objects_allocated); 遍历mem_map这块内存，从begin开始，8字节读一次，转换为Object类型，然后通过vistor 检查是否存在。存在对象和就是上面的对象个数   live_bitmap->VisitMarkedRange(reinterpret_cast<uintptr_t>(mem_map.Begin()),                                 reinterpret_cast<uintptr_t>(mem_map.End()), visitor);   ZygoteSpace* zygote_space = new ZygoteSpace(name, std::move(mem_map), objects_allocated);