runtime/vm/heap/pages.h

// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#ifndef RUNTIME_VM_HEAP_PAGES_H_
#define RUNTIME_VM_HEAP_PAGES_H_

#include "vm/globals.h"
#include "vm/heap/freelist.h"
#include "vm/heap/spaces.h"
#include "vm/lockers.h"
#include "vm/ring_buffer.h"
#include "vm/thread.h"
#include "vm/virtual_memory.h"

namespace dart {

DECLARE_FLAG(bool, log_code_drop);
DECLARE_FLAG(bool, always_drop_code);
DECLARE_FLAG(bool, write_protect_code);

// Forward declarations.
class Heap;
class JSONObject;
class ObjectPointerVisitor;
class ObjectSet;
class ForwardingPage;
class GCMarker;

// TODO(iposva): Determine heap sizes and tune the page size accordingly.
static const intptr_t kPageSize = 256 * KB;
static const intptr_t kPageSizeInWords = kPageSize / kWordSize;
static const intptr_t kPageMask = ~(kPageSize - 1);

// A page containing old generation objects.
class HeapPage {
 public:
  enum PageType { kData = 0, kExecutable, kNumPageTypes };

  HeapPage* next() const { return next_; }
  void set_next(HeapPage* next) { next_ = next; }

  bool Contains(uword addr) { return memory_->Contains(addr); }

  uword object_start() const { return memory_->start() + ObjectStartOffset(); }
  uword object_end() const { return object_end_; }
  uword used_in_bytes() const { return used_in_bytes_; }
  void set_used_in_bytes(uword value) {
    ASSERT(Utils::IsAligned(value, kObjectAlignment));
    used_in_bytes_ = value;
  }

  ForwardingPage* forwarding_page() const { return forwarding_page_; }
  ForwardingPage* AllocateForwardingPage();
  void FreeForwardingPage();

  PageType type() const { return type_; }

  bool is_image_page() const { return !memory_->vm_owns_region(); }

  void VisitObjects(ObjectVisitor* visitor) const;
  void VisitObjectPointers(ObjectPointerVisitor* visitor) const;

  RawObject* FindObject(FindObjectVisitor* visitor) const;

  void WriteProtect(bool read_only);

  static intptr_t ObjectStartOffset() {
    return Utils::RoundUp(sizeof(HeapPage), OS::kMaxPreferredCodeAlignment);
  }

  // Warning: This does not work for objects on image pages because image pages
  // are not aligned.
  static HeapPage* Of(RawObject* obj) {
    ASSERT(obj->IsHeapObject());
    ASSERT(obj->IsOldObject());
    return reinterpret_cast<HeapPage*>(reinterpret_cast<uword>(obj) &
                                       kPageMask);
  }

  static HeapPage* Of(uintptr_t addr) {
    return reinterpret_cast<HeapPage*>(addr & kPageMask);
  }

 private:
  void set_object_end(uword value) {
    ASSERT((value & kObjectAlignmentMask) == kOldObjectAlignmentOffset);
    object_end_ = value;
  }

  // Returns NULL on OOM.
  static HeapPage* Allocate(intptr_t size_in_words,
                            PageType type,
                            const char* name);

  // Deallocate the virtual memory backing this page. The page pointer to this
  // page becomes immediately inaccessible.
  void Deallocate();

  VirtualMemory* memory_;
  HeapPage* next_;
  uword object_end_;
  uword used_in_bytes_;
  ForwardingPage* forwarding_page_;
  PageType type_;

  friend class PageSpace;
  friend class GCCompactor;

  DISALLOW_ALLOCATION();
  DISALLOW_IMPLICIT_CONSTRUCTORS(HeapPage);
};

// The history holds the timing information of the last garbage collection
// runs.
class PageSpaceGarbageCollectionHistory {
 public:
  PageSpaceGarbageCollectionHistory() {}
  ~PageSpaceGarbageCollectionHistory() {}

  void AddGarbageCollectionTime(int64_t start, int64_t end);

  int GarbageCollectionTimeFraction();

  bool IsEmpty() const { return history_.Size() == 0; }

 private:
  struct Entry {
    int64_t start;
    int64_t end;
  };
  static const intptr_t kHistoryLength = 4;
  RingBuffer<Entry, kHistoryLength> history_;

  DISALLOW_ALLOCATION();
  DISALLOW_COPY_AND_ASSIGN(PageSpaceGarbageCollectionHistory);
};

// PageSpaceController controls the heap size.
class PageSpaceController {
 public:
  // The heap is passed in for recording stats only. The controller does not
  // invoke GC by itself.
  PageSpaceController(Heap* heap,
                      int heap_growth_ratio,
                      int heap_growth_max,
                      int garbage_collection_time_ratio);
  ~PageSpaceController();

  // Returns whether growing to 'after' should trigger a GC.
  // This method can be called before allocation (e.g., pretenuring) or after
  // (e.g., promotion), as it does not change the state of the controller.
  bool NeedsGarbageCollection(SpaceUsage after) const;
  bool AlmostNeedsGarbageCollection(SpaceUsage after) const;

  // Returns whether an idle GC is worthwhile.
  bool NeedsIdleGarbageCollection(SpaceUsage current) const;

  // Should be called after each collection to update the controller state.
  void EvaluateGarbageCollection(SpaceUsage before,
                                 SpaceUsage after,
                                 int64_t start,
                                 int64_t end);
  void EvaluateSnapshotLoad(SpaceUsage after);

  int64_t last_code_collection_in_us() { return last_code_collection_in_us_; }
  void set_last_code_collection_in_us(int64_t t) {
    last_code_collection_in_us_ = t;
  }

  void set_last_usage(SpaceUsage current) { last_usage_ = current; }

  void Enable() { is_enabled_ = true; }
  void Disable() { is_enabled_ = false; }
  bool is_enabled() { return is_enabled_; }

 private:
  Heap* heap_;

  bool is_enabled_;

  // Usage after last evaluated GC or last enabled.
  SpaceUsage last_usage_;

  // If the garbage collector was not able to free more than heap_growth_ratio_
  // memory, then the heap is grown. Otherwise garbage collection is performed.
  const int heap_growth_ratio_;

  // The desired percent of heap in-use after a garbage collection.
  // Equivalent to \frac{100-heap_growth_ratio_}{100}.
  const double desired_utilization_;

  // Max number of pages we grow.
  const int heap_growth_max_;

  // If the relative GC time goes above garbage_collection_time_ratio_ %,
  // we grow the heap more aggressively.
  const int garbage_collection_time_ratio_;

  // The time in microseconds of the last time we tried to collect unused
  // code.
  int64_t last_code_collection_in_us_;

  // Perform a synchronous GC when capacity exceeds this amount.
  intptr_t gc_threshold_in_words_;

  // Perform a synchronous GC when external allocations exceed this amount.
  intptr_t gc_external_threshold_in_words_;

  // Start considering idle GC when capacity exceeds this amount.
  intptr_t idle_gc_threshold_in_words_;

  PageSpaceGarbageCollectionHistory history_;

  DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpaceController);
};

class PageSpace {
 public:
  enum GrowthPolicy { kControlGrowth, kForceGrowth };
  enum Phase { kDone, kMarking, kAwaitingFinalization, kSweeping };

  PageSpace(Heap* heap, intptr_t max_capacity_in_words);
  ~PageSpace();

  uword TryAllocate(intptr_t size,
                    HeapPage::PageType type = HeapPage::kData,
                    GrowthPolicy growth_policy = kControlGrowth) {
    bool is_protected =
        (type == HeapPage::kExecutable) && FLAG_write_protect_code;
    bool is_locked = false;
    return TryAllocateInternal(size, type, growth_policy, is_protected,
                               is_locked);
  }

  bool NeedsGarbageCollection() const {
    return page_space_controller_.NeedsGarbageCollection(usage_);
  }
  bool AlmostNeedsGarbageCollection() const {
    return page_space_controller_.AlmostNeedsGarbageCollection(usage_);
  }
  void EvaluateSnapshotLoad() {
    page_space_controller_.EvaluateSnapshotLoad(usage_);
  }

  int64_t UsedInWords() const { return usage_.used_in_words; }
  int64_t CapacityInWords() const {
    MutexLocker ml(pages_lock_);
    return usage_.capacity_in_words;
  }
  void IncreaseCapacityInWords(intptr_t increase_in_words) {
    MutexLocker ml(pages_lock_);
    IncreaseCapacityInWordsLocked(increase_in_words);
  }
  void IncreaseCapacityInWordsLocked(intptr_t increase_in_words) {
    DEBUG_ASSERT(pages_lock_->IsOwnedByCurrentThread());
    usage_.capacity_in_words += increase_in_words;
    UpdateMaxCapacityLocked();
  }

  void UpdateMaxCapacityLocked();
  void UpdateMaxUsed();

  int64_t ExternalInWords() const { return usage_.external_in_words; }
  SpaceUsage GetCurrentUsage() const {
    MutexLocker ml(pages_lock_);
    return usage_;
  }

  bool Contains(uword addr) const;
  bool Contains(uword addr, HeapPage::PageType type) const;
  bool DataContains(uword addr) const;
  bool IsValidAddress(uword addr) const { return Contains(addr); }

  void VisitObjects(ObjectVisitor* visitor) const;
  void VisitObjectsNoImagePages(ObjectVisitor* visitor) const;
  void VisitObjectsImagePages(ObjectVisitor* visitor) const;
  void VisitObjectPointers(ObjectPointerVisitor* visitor) const;

  RawObject* FindObject(FindObjectVisitor* visitor,
                        HeapPage::PageType type) const;

  // Checks if enough time has elapsed since the last attempt to collect
  // code.
  bool ShouldCollectCode();

  // Collect the garbage in the page space using mark-sweep or mark-compact.
  void CollectGarbage(bool compact, bool finalize);

  void AddRegionsToObjectSet(ObjectSet* set) const;

  void InitGrowthControl() {
    page_space_controller_.set_last_usage(usage_);
    page_space_controller_.Enable();
  }

  void SetGrowthControlState(bool state) {
    if (state) {
      page_space_controller_.Enable();
    } else {
      page_space_controller_.Disable();
    }
  }

  bool GrowthControlState() { return page_space_controller_.is_enabled(); }

  // Note: Code pages are made executable/non-executable when 'read_only' is
  // true/false, respectively.
  void WriteProtect(bool read_only);
  void WriteProtectCode(bool read_only);

  bool ShouldPerformIdleMarkSweep(int64_t deadline);
  bool ShouldPerformIdleMarkCompact(int64_t deadline);

  void AddGCTime(int64_t micros) { gc_time_micros_ += micros; }

  int64_t gc_time_micros() const { return gc_time_micros_; }

  void IncrementCollections() { collections_++; }

  intptr_t collections() const { return collections_; }

#ifndef PRODUCT
  void PrintToJSONObject(JSONObject* object) const;
  void PrintHeapMapToJSONStream(Isolate* isolate, JSONStream* stream) const;
#endif  // PRODUCT

  void AllocateBlack(intptr_t size) {
    AtomicOperations::IncrementBy(&allocated_black_in_words_,
                                  size >> kWordSizeLog2);
  }

  void AllocateExternal(intptr_t cid, intptr_t size);
  void FreeExternal(intptr_t size);

  // Bulk data allocation.
  void AcquireDataLock();
  void ReleaseDataLock();

  uword TryAllocateDataLocked(intptr_t size, GrowthPolicy growth_policy) {
    bool is_protected = false;
    bool is_locked = true;
    return TryAllocateInternal(size, HeapPage::kData, growth_policy,
                               is_protected, is_locked);
  }

  Monitor* tasks_lock() const { return tasks_lock_; }
  intptr_t tasks() const { return tasks_; }
  void set_tasks(intptr_t val) {
    ASSERT(val >= 0);
    tasks_ = val;
  }
  intptr_t concurrent_marker_tasks() const { return concurrent_marker_tasks_; }
  void set_concurrent_marker_tasks(intptr_t val) {
    ASSERT(val >= 0);
    concurrent_marker_tasks_ = val;
  }
  Phase phase() const { return phase_; }
  void set_phase(Phase val) { phase_ = val; }

  // Attempt to allocate from bump block rather than normal freelist.
  uword TryAllocateDataBump(intptr_t size, GrowthPolicy growth_policy);
  uword TryAllocateDataBumpLocked(intptr_t size, GrowthPolicy growth_policy);
  // Prefer small freelist blocks, then chip away at the bump block.
  uword TryAllocatePromoLocked(intptr_t size, GrowthPolicy growth_policy);

  void SetupImagePage(void* pointer, uword size, bool is_executable);

  // Return any bump allocation block to the freelist.
  void AbandonBumpAllocation();
  // Have threads release marking stack blocks, etc.
  void AbandonMarkingForShutdown();

 private:
  // Ids for time and data records in Heap::GCStats.
  enum {
    // Time
    kConcurrentSweep = 0,
    kSafePoint = 1,
    kMarkObjects = 2,
    kResetFreeLists = 3,
    kSweepPages = 4,
    kSweepLargePages = 5,
    // Data
    kGarbageRatio = 0,
    kGCTimeFraction = 1,
    kPageGrowth = 2,
    kAllowedGrowth = 3
  };

  static const intptr_t kAllocatablePageSize = 64 * KB;

  uword TryAllocateInternal(intptr_t size,
                            HeapPage::PageType type,
                            GrowthPolicy growth_policy,
                            bool is_protected,
                            bool is_locked);
  uword TryAllocateInFreshPage(intptr_t size,
                               HeapPage::PageType type,
                               GrowthPolicy growth_policy,
                               bool is_locked);
  uword TryAllocateDataBumpInternal(intptr_t size,
                                    GrowthPolicy growth_policy,
                                    bool is_locked);
  // Makes bump block walkable; do not call concurrently with mutator.
  void MakeIterable() const;
  HeapPage* AllocatePage(HeapPage::PageType type);
  void FreePage(HeapPage* page, HeapPage* previous_page);
  HeapPage* AllocateLargePage(intptr_t size, HeapPage::PageType type);
  void TruncateLargePage(HeapPage* page, intptr_t new_object_size_in_bytes);
  void FreeLargePage(HeapPage* page, HeapPage* previous_page);
  void FreePages(HeapPage* pages);

  void CollectGarbageAtSafepoint(bool compact,
                                 bool finalize,
                                 int64_t pre_wait_for_sweepers,
                                 int64_t pre_safe_point);
  void BlockingSweep();
  void ConcurrentSweep(Isolate* isolate);
  void Compact(Thread* thread);

  static intptr_t LargePageSizeInWordsFor(intptr_t size);

  bool CanIncreaseCapacityInWords(intptr_t increase_in_words) {
    if (max_capacity_in_words_ == 0) {
      // Unlimited.
      return true;
    }
    // TODO(issue 27413): Make the check against capacity and the bump
    // of capacity atomic so that CapacityInWords does not exceed
    // max_capacity_in_words_.
    intptr_t free_capacity_in_words =
        (max_capacity_in_words_ - CapacityInWords());
    return ((free_capacity_in_words > 0) &&
            (increase_in_words <= free_capacity_in_words));
  }

  FreeList freelist_[HeapPage::kNumPageTypes];

  Heap* heap_;

  // Use ExclusivePageIterator for safe access to these.
  Mutex* pages_lock_;
  HeapPage* pages_;
  HeapPage* pages_tail_;
  HeapPage* exec_pages_;
  HeapPage* exec_pages_tail_;
  HeapPage* large_pages_;
  HeapPage* image_pages_;

  // A block of memory in a data page, managed by bump allocation. The remainder
  // is kept formatted as a FreeListElement, but is not in any freelist.
  uword bump_top_;
  uword bump_end_;

  // Various sizes being tracked for this generation.
  intptr_t max_capacity_in_words_;

  // NOTE: The capacity component of usage_ is updated by the concurrent
  // sweeper. Use (Increase)CapacityInWords(Locked) for thread-safe access.
  SpaceUsage usage_;
  intptr_t allocated_black_in_words_;

  // Keep track of running MarkSweep tasks.
  Monitor* tasks_lock_;
  intptr_t tasks_;
  intptr_t concurrent_marker_tasks_;
  Phase phase_;

#if defined(DEBUG)
  Thread* iterating_thread_;
#endif
  PageSpaceController page_space_controller_;
  GCMarker* marker_;

  int64_t gc_time_micros_;
  intptr_t collections_;
  intptr_t mark_words_per_micro_;

  friend class ExclusivePageIterator;
  friend class ExclusiveCodePageIterator;
  friend class ExclusiveLargePageIterator;
  friend class HeapIterationScope;
  friend class PageSpaceController;
  friend class SweeperTask;
  friend class GCCompactor;
  friend class CompactorTask;

  DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
};

}  // namespace dart

#endif  // RUNTIME_VM_HEAP_PAGES_H_