Revert of Pool implementation for zone segments

src/zone/accounting-allocator.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ZONE_ACCOUNTING_ALLOCATOR_H_
 #define V8_ZONE_ACCOUNTING_ALLOCATOR_H_
 
 #include "include/v8-platform.h"
 #include "src/base/atomic-utils.h"
 #include "src/base/atomicops.h"
 #include "src/base/macros.h"
 #include "src/base/platform/mutex.h"
 #include "src/base/platform/semaphore.h"
 #include "src/base/platform/time.h"
 #include "src/zone/zone-segment.h"
 
 namespace v8 {
 namespace internal {
 
 class V8_EXPORT_PRIVATE AccountingAllocator {
  public:
-  AccountingAllocator();
-  virtual ~AccountingAllocator();
+  AccountingAllocator() = default;
+  virtual ~AccountingAllocator() = default;
 
-  // 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);
+  virtual Segment* AllocateSegment(size_t bytes);
+  virtual void FreeSegment(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);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ZONE_ACCOUNTING_ALLOCATOR_H_