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 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 pool or creates a new one.
+  virtual Segment* GetSegment(size_t bytes);
+  // Return non needed segments here to insert them into the pool
+  // or release them in case the pool is full. Operation may or may
+  // not be asynchronous, depending on memory pressure.
+  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);
+
+  // Allocated a new segment. Returns nullptr on failed allocation.
+  Segment* AllocateSegment(size_t bytes);
+  // Frees a non needed segment. Blocks the current thread.
+  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_ =

[Toon Verwaest, 2016/09/21 11:18:07]

Segment* unused_segments_heads_[1+kMax-kMin], same for sizes.

[heimbuef, 2016/09/21 11:39:23]

Format checker does not like no spaces in between operands and operators. Also,
this does not work because it would mean that the head-segments would be stored
actually in the accounting-allocator. They can't, because they *are* just the
headers of the chunks of memory we dynamically allocate and free here.

+      new Segment*[1 + kMaxSegmentSizePower - kMinSegmentSizePower];
+
+  size_t* unused_segments_sizes =
+      new size_t[1 + kMaxSegmentSizePower - kMinSegmentSizePower];
+
+  size_t unused_segments_size_ = 0;
+
+  base::Mutex* unused_segments_mutex_ = new base::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_