Simple BlinkGC heap compaction.

third_party/WebKit/Source/platform/heap/HeapCompact.h

+// Copyright 2016 Opera Software AS. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef HeapCompact_h
+#define HeapCompact_h
+
+#include "platform/PlatformExport.h"
+#include "platform/heap/BlinkGC.h"
+#include "wtf/PtrUtil.h"
+#include "wtf/Vector.h"
+
+#include <bitset>
+#include <utility>
+
+// Global dev/debug switches:
+
+// Set to 0 to prevent compaction GCs, disabling the heap compaction feature.
+#define ENABLE_HEAP_COMPACTION 1
+
+// Emit debug info during compaction.
+#define DEBUG_HEAP_COMPACTION 0
+
+// Emit stats on freelist occupancy.
+// 0 - disabled, 1 - minimal, 2 - verbose.
+#define DEBUG_HEAP_FREELIST 0
+
+// Log the amount of time spent compacting.
+#define DEBUG_LOG_HEAP_COMPACTION_RUNNING_TIME 0
+
+// Compact during all idle + precise GCs; for debugging.
+#define STRESS_TEST_HEAP_COMPACTION 0
+
+#if OS(WIN)
+// TODO: use standard logging facilities.
+#define LOG_HEAP_COMPACTION_INTERNAL(msg, ...) \
+  do {                                         \
+    char output[512];                          \
+    sprintf(output, msg, ##__VA_ARGS__);       \
+    OutputDebugStringA(output);                \
+  } while (0)
+#else
+#define LOG_HEAP_COMPACTION_INTERNAL(msg, ...) \
+  fprintf(stderr, msg, ##__VA_ARGS__)
+#endif
+
+#if DEBUG_HEAP_COMPACTION
+#define LOG_HEAP_COMPACTION(msg, ...) \
+  LOG_HEAP_COMPACTION_INTERNAL(msg, ##__VA_ARGS__)
+#else
+#define LOG_HEAP_COMPACTION(msg, ...) \
+  do {                                \
+  } while (0)
+#endif
+
+#if DEBUG_HEAP_FREELIST
+#define LOG_HEAP_FREELIST(msg, ...) \
+  LOG_HEAP_COMPACTION_INTERNAL(msg, ##__VA_ARGS__)
+#else
+#define LOG_HEAP_FREELIST(msg, ...) \
+  do {                              \
+  } while (0)
+#endif
+
+#if DEBUG_HEAP_FREELIST == 2
+#define LOG_HEAP_FREELIST_VERBOSE(msg, ...) \
+  LOG_HEAP_COMPACTION_INTERNAL(msg, ##__VA_ARGS__)
+#else
+#define LOG_HEAP_FREELIST_VERBOSE(msg, ...) \
+  do {                                      \
+  } while (0)
+#endif
+
+namespace blink {
+
+class NormalPageArena;
+class BasePage;
+class ThreadHeap;
+class ThreadState;
+
+class PLATFORM_EXPORT HeapCompact final {
+ public:
+  static std::unique_ptr<HeapCompact> create() {
+    return std::unique_ptr<HeapCompact>(new HeapCompact);
+  }
+
+  ~HeapCompact();
+
+  // Check if a GC for the given type and reason should perform additional
+  // heap compaction once it has run.
+  //
+  // If deemed worthy, heap compaction is implicitly initialized and set up.
+  void checkIfCompacting(ThreadHeap*,
+                         Visitor*,
+                         BlinkGC::GCType,
+                         BlinkGC::GCReason);
+
+  // Returns true if the ongoing GC will perform compaction.
+  bool isCompacting() const { return m_doCompact; }
+
+  // Returns true if the ongoing GC will perform compaction.
+  bool isCompactingArena(int arenaIndex) const {
+    return m_doCompact && (m_compactableHeaps & (0x1u << arenaIndex));
+  }
+
+  // Returns |true| if the ongoing GC may compact the given arena/sub-heap.
+  static bool isCompactableArena(int arenaIndex) {
+    return arenaIndex >= BlinkGC::Vector1ArenaIndex &&
+           arenaIndex <= BlinkGC::HashTableArenaIndex;
+  }
+
+  // See |Heap::registerMovingObjectReference()| documentation.
+  void registerMovingObjectReference(MovableReference* slot);
+
+  // See |Heap::registerMovingObjectCallback()| documentation.
+  void registerMovingObjectCallback(MovableReference,
+                                    MovingObjectCallback,
+                                    void* callbackData);
+
+  // Register |slot| as containing a reference to the interior of a movable
+  // object.
+  //
+  // |registerMovingObjectReference()| handles the common case of holding an
+  // external
+  // reference to a backing store object. |registerRelocation()| handles the
+  // relocation
+  // of external references into backing store objects - something very rarely
+  // done by
+  // the Blink codebase, but a possibility.
+  void registerRelocation(MovableReference* slot);
+
+  // Signal that the compaction pass is being started, finished by some
+  // ThreadState.
+  void startCompacting(ThreadState*);
+  void finishedCompacting(ThreadState*);
+
+  // Perform any relocation post-processing after having completed compacting
+  // the
+  // given sub heap. Pass along the number of pages that were freed from the
+  // arena,
+  // along with their total size.
+  void finishedArenaCompaction(NormalPageArena*,
+                               size_t freedPages,
+                               size_t freedSize);
+
+  // Record the main thread's compactable freelist residency (in bytes),
+  // along with with overall size. Sizes are relative to the compactable
+  // sub-heaps, and not a total count. Along with the totals, per-heap
+  // numbers are also provided.
+  //
+  // The recording is done after the decision has been made on whether
+  // or not to compact during the _current_ GC. If compacting, the size
+  // sampling will be ignored and the internal counters are reset.
+  //
+  // However, if not compacting, the values will be consulted the next time
+  // a GC goes ahead and it decides whether to compact or not.
+  void setHeapResidency(
+      size_t liveSize,
+      size_t freeSize,
+      const Vector<std::pair<size_t, size_t>>& heapResidencies);
+
+  // Register the heap page as containing live objects that will all be
+  // compacted. When the GC is compacting, that is.
+  void addCompactablePage(BasePage*);
+
+  // Notify heap compaction that object at |from| has been moved to.. |to|.
+  // (Called by the sweep compaction pass.)
+  void movedObject(Address from, Address to);
+
+  // For unit testing only: arrange for a compaction GC to be triggered
+  // next time a non-conservative GC is run. Sets the compact-next flag
+  // to the new value, returning old.
+  static bool scheduleCompactionGCForTesting(bool);
+
+ private:
+  class MovableObjectFixups;
+
+  HeapCompact();
+
+  // Parameters controlling when compaction should be done:
+
+  // Number of GCs that must have passed since last compaction GC.
+  static const int kCompactIntervalThreshold = 10;
+
+  // Freelist size threshold that must be exceeded before compaction
+  // should be considered.
+  static const size_t kFreeThreshold = 512 * 1024;
+
+  MovableObjectFixups& fixups();
+
+  std::unique_ptr<MovableObjectFixups> m_fixups;
+
+  // Set to |true| when a compacting sweep will go ahead.
+  bool m_doCompact;
+  size_t m_gcCountSinceLastCompaction;
+
+  // Number of heap threads participating in the compaction.
+  int m_threadCount;
+
+  // Last reported freelist size, across all heaps.
+  size_t m_freeListAllocations;
+  // If compacting, i'th sub heap will be compacted
+  // if corresponding bit is set.
+  unsigned m_compactableHeaps;
+
+  // Stats, number of (complete) pages freed/decommitted +
+  // bytes freed (which will include partial pages.)
+  size_t m_freedPages;
+  size_t m_freedSize;
+
+#if DEBUG_LOG_HEAP_COMPACTION_RUNNING_TIME
+  int m_startCompaction;
+  double m_startCompactionTimeMS;
+#endif
+
+  static bool s_forceCompactionGC;
+};
+
+}  // namespace blink
+
+#endif  // HeapCompact_h