Pool implementation for zone segments

src/zone/accounting-allocator.h

Index: src/zone/accounting-allocator.h
diff --git a/src/zone/accounting-allocator.h b/src/zone/accounting-allocator.h
index 31016a5018326d8c89e7cf1fd779ce111da5b2bb..6a32e18af7b8daaab93789e1e1b8dd8bf314525c 100644
--- a/src/zone/accounting-allocator.h
+++ b/src/zone/accounting-allocator.h
@@ -19,19 +19,55 @@ namespace internal {
 
 class V8_EXPORT_PRIVATE AccountingAllocator {
  public:
-  AccountingAllocator() = default;
-  virtual ~AccountingAllocator() = default;
+  AccountingAllocator();
+  virtual ~AccountingAllocator();
 
-  virtual Segment* AllocateSegment(size_t bytes);
-  virtual void FreeSegment(Segment* memory);
+  // Gets an empty segment from the pool or creates a new one.
+  virtual Segment* GetSegment(size_t bytes);
+  // Return unneeded segments to either insert them into the pool or release
+  // them if the pool is already full or memory pressure is high.
+  virtual void ReturnSegment(Segment* memory);
 
   size_t GetCurrentMemoryUsage() const;
   size_t GetMaxMemoryUsage() const;
 
+  size_t GetCurrentPoolSize() const;
+
+  void MemoryPressureNotification(MemoryPressureLevel level);
+
  private:
+  static const uint8_t kMinSegmentSizePower = 13;
+  static const uint8_t kMaxSegmentSizePower = 18;
+  static const uint8_t kMaxSegmentsPerBucket = 5;
+
+  STATIC_ASSERT(kMinSegmentSizePower <= kMaxSegmentSizePower);
+
+  // Allocates a new segment. Returns nullptr on failed allocation.
+  Segment* AllocateSegment(size_t bytes);
+  void FreeSegment(Segment* memory);
+
+  // Returns a segment from the pool of at least the requested size.
+  Segment* GetSegmentFromPool(size_t requested_size);
+  // Trys to add a segment to the pool. Returns false if the pool is full.
+  bool AddSegmentToPool(Segment* segment);
+
+  // Empties the pool and puts all its contents onto the garbage stack.
+  void ClearPool();
+
+  Segment*
+      unused_segments_heads_[1 + kMaxSegmentSizePower - kMinSegmentSizePower];
+
+  size_t unused_segments_sizes[1 + kMaxSegmentSizePower - kMinSegmentSizePower];
+
+  size_t unused_segments_size_ = 0;
+
+  base::Mutex unused_segments_mutex_;
+
   base::AtomicWord current_memory_usage_ = 0;
   base::AtomicWord max_memory_usage_ = 0;
 
+  base::AtomicValue<MemoryPressureLevel> memory_pressure_level_;
+
   DISALLOW_COPY_AND_ASSIGN(AccountingAllocator);
 };