Revert "[heap] Refactor allocation observer in AllocationCounter"

This reverts commit b354e344.

Reason for revert: Clusterfuzz found issues with this CL.

Original change's description:
> [heap] Refactor allocation observer in AllocationCounter
> 
> Moves accounting of allocation observers into the AllocationCounter
> class. This CL removes top_on_previous_step_ for counters that are
> increased regularly in the slow path of the allocation functions.
> 
> AdvanceAllocationObservers() informs the AllocationCounter about
> allocated bytes, InvokeAllocationObservers() needs to be invoked when
> an allocation step is reached. NextBytes() returns the number of bytes
> until the next AllocationObserver::Step needs to run.
> 
> Bug: v8:10315
> Change-Id: I8b6eb8719ab032d44ee0614d2a0f2645bfce9df6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2320650
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#69170}

TBR=ulan@chromium.org,dinfuehr@chromium.org

Change-Id: Icd713207bfb2085421fd82009be24a0211ae86da
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10315
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332667Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69187}

src/heap/allocation-observer.cc

@@ -11,97 +11,70 @@ namespace v8 {
 namespace internal {
 
 void AllocationCounter::AddAllocationObserver(AllocationObserver* observer) {
-  intptr_t step_size = observer->GetNextStepSize();
-  size_t observer_next_counter = current_counter_ + step_size;
-
-#if DEBUG
-  auto it =
-      std::find_if(observers_.begin(), observers_.end(),
-                   [observer](const ObserverAccounting& observer_accounting) {
-                     return observer_accounting.observer_ == observer;
-                   });
-  DCHECK_EQ(observers_.end(), it);
-#endif
-
-  observers_.push_back(
-      ObserverAccounting(observer, current_counter_, observer_next_counter));
-
-  if (observers_.size() == 1) {
-    DCHECK_EQ(current_counter_, next_counter_);
-    next_counter_ = observer_next_counter;
-  } else {
-    size_t missing_bytes = next_counter_ - current_counter_;
-    next_counter_ =
-        current_counter_ + Min(static_cast<intptr_t>(missing_bytes), step_size);
-  }
+  allocation_observers_.push_back(observer);
 }
 
 void AllocationCounter::RemoveAllocationObserver(AllocationObserver* observer) {
-  auto it =
-      std::find_if(observers_.begin(), observers_.end(),
-                   [observer](const ObserverAccounting& observer_accounting) {
-                     return observer_accounting.observer_ == observer;
-                   });
-  DCHECK_NE(observers_.end(), it);
-  observers_.erase(it);
-
-  if (observers_.size() == 0) {
-    current_counter_ = next_counter_ = 0;
-  } else {
-    size_t step_size = 0;
-
-    for (ObserverAccounting& observer : observers_) {
-      size_t left_in_step = observer.next_counter_ - current_counter_;
-      DCHECK_GT(left_in_step, 0);
-      step_size = step_size ? Min(step_size, left_in_step) : left_in_step;
-    }
-
-    next_counter_ = current_counter_ + step_size;
+  auto it = std::find(allocation_observers_.begin(),
+                      allocation_observers_.end(), observer);
+  DCHECK(allocation_observers_.end() != it);
+  allocation_observers_.erase(it);
+}
+
+intptr_t AllocationCounter::GetNextInlineAllocationStepSize() {
+  intptr_t next_step = 0;
+  for (AllocationObserver* observer : allocation_observers_) {
+    next_step = next_step ? Min(next_step, observer->bytes_to_next_step())
+                          : observer->bytes_to_next_step();
   }
+  DCHECK(!HasAllocationObservers() || next_step > 0);
+  return next_step;
 }
 
-void AllocationCounter::AdvanceAllocationObservers(size_t allocated) {
+void AllocationCounter::NotifyBytes(size_t allocated) {
   if (!IsActive()) {
     return;
   }
 
-  DCHECK_LT(allocated, next_counter_ - current_counter_);
+  DCHECK_LE(allocated, next_counter_ - current_counter_);
   current_counter_ += allocated;
 }
 
-void AllocationCounter::InvokeAllocationObservers(Address soon_object,
-                                                  size_t object_size,
-                                                  size_t aligned_object_size) {
+void AllocationCounter::NotifyObject(Address soon_object, size_t object_size) {
   if (!IsActive()) {
     return;
   }
 
-  DCHECK_GE(aligned_object_size, next_counter_ - current_counter_);
+  DCHECK_GT(object_size, next_counter_ - current_counter_);
+  size_t bytes_since_last_step = current_counter_ - prev_counter_;
+  DCHECK(!heap_->allocation_step_in_progress());
+  heap_->set_allocation_step_in_progress(true);
   DCHECK(soon_object);
-  size_t step_size = 0;
-  bool step_run = false;
-  for (ObserverAccounting& observer_accounting : observers_) {
-    if (observer_accounting.next_counter_ - current_counter_ <=
-        aligned_object_size) {
-      observer_accounting.observer_->Step(
-          static_cast<int>(current_counter_ -
-                           observer_accounting.prev_counter_),
-          soon_object, object_size);
-      size_t observer_step_size =
-          observer_accounting.observer_->GetNextStepSize();
-
-      observer_accounting.prev_counter_ = current_counter_;
-      observer_accounting.next_counter_ =
-          current_counter_ + aligned_object_size + observer_step_size;
-      step_run = true;
-    }
-
-    size_t left_in_step = observer_accounting.next_counter_ - current_counter_;
-    step_size = step_size ? Min(step_size, left_in_step) : left_in_step;
+  heap_->CreateFillerObjectAt(soon_object, static_cast<int>(object_size),
+                              ClearRecordedSlots::kNo);
+  intptr_t next_step = 0;
+  for (AllocationObserver* observer : allocation_observers_) {
+    observer->AllocationStep(static_cast<int>(bytes_since_last_step),
+                             soon_object, object_size);
+    next_step = next_step ? Min(next_step, observer->bytes_to_next_step())
+                          : observer->bytes_to_next_step();
   }
+  heap_->set_allocation_step_in_progress(false);
 
-  CHECK(step_run);
-  next_counter_ = current_counter_ + step_size;
+  prev_counter_ = current_counter_;
+  next_counter_ = current_counter_ + object_size + next_step;
+}
+
+void AllocationObserver::AllocationStep(int bytes_allocated,
+                                        Address soon_object, size_t size) {
+  DCHECK_GE(bytes_allocated, 0);
+  bytes_to_next_step_ -= bytes_allocated;
+  if (bytes_to_next_step_ <= 0) {
+    Step(static_cast<int>(step_size_ - bytes_to_next_step_), soon_object, size);
+    step_size_ = GetNextStepSize();
+    bytes_to_next_step_ = step_size_;
+  }
+  DCHECK_GE(bytes_to_next_step_, 0);
 }
 
 PauseAllocationObserversScope::PauseAllocationObserversScope(Heap* heap)

src/heap/allocation-observer.h

@@ -5,7 +5,6 @@
 #ifndef V8_HEAP_ALLOCATION_OBSERVER_H_
 #define V8_HEAP_ALLOCATION_OBSERVER_H_
 
-#include <cstdint>
 #include <vector>
 
 #include "src/common/globals.h"
@@ -14,14 +13,27 @@ namespace v8 {
 namespace internal {
 
 class AllocationObserver;
+class Heap;
 
 class AllocationCounter {
  public:
-  AllocationCounter() : paused_(false), current_counter_(0), next_counter_(0) {}
-  V8_EXPORT_PRIVATE void AddAllocationObserver(AllocationObserver* observer);
-  V8_EXPORT_PRIVATE void RemoveAllocationObserver(AllocationObserver* observer);
+  explicit AllocationCounter(Heap* heap)
+      : heap_(heap),
+        paused_(false),
+        prev_counter_(0),
+        current_counter_(0),
+        next_counter_(0) {}
 
-  bool IsActive() { return !IsPaused() && observers_.size() > 0; }
+  auto begin() { return allocation_observers_.begin(); }
+  auto end() { return allocation_observers_.end(); }
+
+  void AddAllocationObserver(AllocationObserver* observer);
+  void RemoveAllocationObserver(AllocationObserver* observer);
+
+  bool HasAllocationObservers() { return !allocation_observers_.empty(); }
+  size_t NumberAllocationObservers() { return allocation_observers_.size(); }
+
+  bool IsActive() { return !IsPaused() && HasAllocationObservers(); }
 
   void Pause() {
     DCHECK(!paused_);
@@ -33,10 +45,10 @@ class AllocationCounter {
     paused_ = false;
   }
 
-  V8_EXPORT_PRIVATE void AdvanceAllocationObservers(size_t allocated);
-  V8_EXPORT_PRIVATE void InvokeAllocationObservers(Address soon_object,
-                                                   size_t object_size,
-                                                   size_t aligned_object_size);
+  intptr_t GetNextInlineAllocationStepSize();
+
+  void NotifyBytes(size_t allocated);
+  void NotifyObject(Address soon_object, size_t object_size);
 
   size_t NextBytes() {
     DCHECK(IsActive());
@@ -46,22 +58,11 @@ class AllocationCounter {
  private:
   bool IsPaused() { return paused_; }
 
-  struct ObserverAccounting {
-    ObserverAccounting(AllocationObserver* observer, size_t prev_counter,
-                       size_t next_counter)
-        : observer_(observer),
-          prev_counter_(prev_counter),
-          next_counter_(next_counter) {}
-
-    AllocationObserver* observer_;
-    size_t prev_counter_;
-    size_t next_counter_;
-  };
-
-  std::vector<ObserverAccounting> observers_;
-
+  std::vector<AllocationObserver*> allocation_observers_;
+  Heap* heap_;
   bool paused_;
 
+  size_t prev_counter_;
   size_t current_counter_;
   size_t next_counter_;
 };
@@ -70,12 +71,21 @@ class AllocationCounter {
 // Allows observation of allocations.
 class AllocationObserver {
  public:
-  explicit AllocationObserver(intptr_t step_size) : step_size_(step_size) {
+  explicit AllocationObserver(intptr_t step_size)
+      : step_size_(step_size), bytes_to_next_step_(step_size) {
     DCHECK_LE(kTaggedSize, step_size);
   }
   virtual ~AllocationObserver() = default;
 
+  // Called each time the observed space does an allocation step. This may be
+  // more frequently than the step_size we are monitoring (e.g. when there are
+  // multiple observers, or when page or space boundary is encountered.)
+  void AllocationStep(int bytes_allocated, Address soon_object, size_t size);
+
  protected:
+  intptr_t step_size() const { return step_size_; }
+  intptr_t bytes_to_next_step() const { return bytes_to_next_step_; }
+
   // Pure virtual method provided by the subclasses that gets called when at
   // least step_size bytes have been allocated. soon_object is the address just
   // allocated (but not yet initialized.) size is the size of the object as
@@ -93,9 +103,10 @@ class AllocationObserver {
   // Subclasses can override this method to make step size dynamic.
   virtual intptr_t GetNextStepSize() { return step_size_; }
 
- private:
   intptr_t step_size_;
+  intptr_t bytes_to_next_step_;
 
+ private:
   friend class AllocationCounter;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };

src/heap/heap-inl.h

@@ -66,11 +66,6 @@ HeapObject AllocationResult::ToObject() {
   return HeapObject::cast(object_);
 }
 
-Address AllocationResult::ToAddress() {
-  DCHECK(!IsRetry());
-  return HeapObject::cast(object_).address();
-}
-
 Isolate* Heap::isolate() {
   return reinterpret_cast<Isolate*>(
       reinterpret_cast<intptr_t>(this) -

src/heap/heap.cc

@@ -900,7 +900,6 @@ void Heap::MergeAllocationSitePretenuringFeedback(
 void Heap::AddAllocationObserversToAllSpaces(
     AllocationObserver* observer, AllocationObserver* new_space_observer) {
   DCHECK(observer && new_space_observer);
-  SafepointScope scope(this);
 
   for (SpaceIterator it(this); it.HasNext();) {
     Space* space = it.Next();
@@ -915,7 +914,6 @@ void Heap::AddAllocationObserversToAllSpaces(
 void Heap::RemoveAllocationObserversFromAllSpaces(
     AllocationObserver* observer, AllocationObserver* new_space_observer) {
   DCHECK(observer && new_space_observer);
-  SafepointScope scope(this);
 
   for (SpaceIterator it(this); it.HasNext();) {
     Space* space = it.Next();
@@ -5129,7 +5127,6 @@ void Heap::EnableInlineAllocation() {
   inline_allocation_disabled_ = false;
 
   // Update inline allocation limit for new space.
-  new_space()->AdvanceAllocationObservers();
   new_space()->UpdateInlineAllocationLimit(0);
 }
 

src/heap/heap.h

@@ -197,7 +197,6 @@ class AllocationResult {
   inline bool IsRetry() { return object_.IsSmi(); }
   inline HeapObject ToObjectChecked();
   inline HeapObject ToObject();
-  inline Address ToAddress();
   inline AllocationSpace RetrySpace();
 
   template <typename T>
@@ -1396,6 +1395,11 @@ class Heap {
   void RemoveAllocationObserversFromAllSpaces(
       AllocationObserver* observer, AllocationObserver* new_space_observer);
 
+  bool allocation_step_in_progress() { return allocation_step_in_progress_; }
+  void set_allocation_step_in_progress(bool val) {
+    allocation_step_in_progress_ = val;
+  }
+
   // ===========================================================================
   // Heap object allocation tracking. ==========================================
   // ===========================================================================
@@ -2075,6 +2079,8 @@ class Heap {
   // Observer that can cause early scavenge start.
   StressScavengeObserver* stress_scavenge_observer_ = nullptr;
 
+  bool allocation_step_in_progress_ = false;
+
   // The maximum percent of the marking limit reached wihout causing marking.
   // This is tracked when specyfing --fuzzer-gc-analysis.
   double max_marking_limit_reached_ = 0.0;

src/heap/large-spaces.cc

@@ -108,19 +108,6 @@ void LargeObjectSpace::TearDown() {
   }
 }
 
-void LargeObjectSpace::AdvanceAndInvokeAllocationObservers(Address soon_object,
-                                                           size_t object_size) {
-  if (!allocation_counter_.IsActive()) return;
-
-  if (object_size >= allocation_counter_.NextBytes()) {
-    allocation_counter_.InvokeAllocationObservers(soon_object, object_size,
-                                                  object_size);
-  }
-
-  // Large objects can be accounted immediately since no LAB is involved.
-  allocation_counter_.AdvanceAllocationObservers(object_size);
-}
-
 AllocationResult OldLargeObjectSpace::AllocateRaw(int object_size) {
   return AllocateRaw(object_size, NOT_EXECUTABLE);
 }
@@ -149,8 +136,7 @@ AllocationResult OldLargeObjectSpace::AllocateRaw(int object_size,
       heap()->incremental_marking()->marking_state()->IsBlack(object));
   page->InitializationMemoryFence();
   heap()->NotifyOldGenerationExpansion(identity(), page);
-  AdvanceAndInvokeAllocationObservers(object.address(),
-                                      static_cast<size_t>(object_size));
+  AllocationStep(object_size, object.address(), object_size);
   return object;
 }
 
@@ -472,8 +458,7 @@ AllocationResult NewLargeObjectSpace::AllocateRaw(int object_size) {
   page->InitializationMemoryFence();
   DCHECK(page->IsLargePage());
   DCHECK_EQ(page->owner_identity(), NEW_LO_SPACE);
-  AdvanceAndInvokeAllocationObservers(result.address(),
-                                      static_cast<size_t>(object_size));
+  AllocationStep(object_size, result.address(), object_size);
   return result;
 }
 

src/heap/large-spaces.h

@@ -113,8 +113,6 @@ class V8_EXPORT_PRIVATE LargeObjectSpace : public Space {
  protected:
   LargeObjectSpace(Heap* heap, AllocationSpace id);
 
-  void AdvanceAndInvokeAllocationObservers(Address soon_object, size_t size);
-
   LargePage* AllocateLargePage(int object_size, Executability executable);
 
   size_t size_;          // allocated bytes

src/heap/new-spaces-inl.h

@@ -90,7 +90,7 @@ AllocationResult NewSpace::AllocateRaw(int size_in_bytes,
   AllocationResult result;
 
   if (alignment != kWordAligned) {
-    result = AllocateFastAligned(size_in_bytes, nullptr, alignment, origin);
+    result = AllocateFastAligned(size_in_bytes, alignment, origin);
   } else {
     result = AllocateFastUnaligned(size_in_bytes, origin);
   }
@@ -122,9 +122,9 @@ AllocationResult NewSpace::AllocateFastUnaligned(int size_in_bytes,
   return obj;
 }
 
-AllocationResult NewSpace::AllocateFastAligned(
-    int size_in_bytes, int* result_aligned_size_in_bytes,
-    AllocationAlignment alignment, AllocationOrigin origin) {
+AllocationResult NewSpace::AllocateFastAligned(int size_in_bytes,
+                                               AllocationAlignment alignment,
+                                               AllocationOrigin origin) {
   Address top = allocation_info_.top();
   int filler_size = Heap::GetFillToAlign(top, alignment);
   int aligned_size_in_bytes = size_in_bytes + filler_size;
@@ -136,8 +136,6 @@ AllocationResult NewSpace::AllocateFastAligned(
 
   HeapObject obj = HeapObject::FromAddress(top);
   allocation_info_.set_top(top + aligned_size_in_bytes);
-  if (result_aligned_size_in_bytes)
-    *result_aligned_size_in_bytes = aligned_size_in_bytes;
   DCHECK_SEMISPACE_ALLOCATION_INFO(allocation_info_, to_space_);
 
   if (filler_size > 0) {

src/heap/new-spaces.cc

@@ -465,7 +465,8 @@ bool NewSpace::Rebalance() {
 }
 
 void NewSpace::UpdateLinearAllocationArea() {
-  AdvanceAllocationObservers();
+  // Make sure there is no unaccounted allocations.
+  DCHECK(!allocation_counter_.IsActive() || top_on_previous_step_ == top());
 
   Address new_top = to_space_.page_low();
   BasicMemoryChunk::UpdateHighWaterMark(allocation_info_.top());
@@ -474,10 +475,13 @@ void NewSpace::UpdateLinearAllocationArea() {
   // See the corresponding loads in ConcurrentMarking::Run.
   original_limit_.store(limit(), std::memory_order_relaxed);
   original_top_.store(top(), std::memory_order_release);
+  StartNextInlineAllocationStep();
   DCHECK_SEMISPACE_ALLOCATION_INFO(allocation_info_, to_space_);
 }
 
 void NewSpace::ResetLinearAllocationArea() {
+  // Do a step to account for memory allocated so far before resetting.
+  InlineAllocationStep(top(), top(), kNullAddress, 0);
   to_space_.Reset();
   UpdateLinearAllocationArea();
   // Clear all mark-bits in the to-space.
@@ -502,6 +506,9 @@ bool NewSpace::AddFreshPage() {
   Address top = allocation_info_.top();
   DCHECK(!OldSpace::IsAtPageStart(top));
 
+  // Do a step to account for memory allocated on previous page.
+  InlineAllocationStep(top, top, kNullAddress, 0);
+
   if (!to_space_.AdvancePage()) {
     // No more pages left to advance.
     return false;
@@ -523,30 +530,34 @@ bool NewSpace::AddFreshPageSynchronized() {
 
 bool NewSpace::EnsureAllocation(int size_in_bytes,
                                 AllocationAlignment alignment) {
-  AdvanceAllocationObservers();
-
   Address old_top = allocation_info_.top();
   Address high = to_space_.page_high();
   int filler_size = Heap::GetFillToAlign(old_top, alignment);
   int aligned_size_in_bytes = size_in_bytes + filler_size;
 
-  if (old_top + aligned_size_in_bytes <= high) {
-    UpdateInlineAllocationLimit(aligned_size_in_bytes);
-    return true;
-  }
+  if (old_top + aligned_size_in_bytes > high) {
+    // Not enough room in the page, try to allocate a new one.
+    if (!AddFreshPage()) {
+      return false;
+    }
 
-  // Not enough room in the page, try to allocate a new one.
-  if (!AddFreshPage()) {
-    return false;
+    old_top = allocation_info_.top();
+    high = to_space_.page_high();
+    filler_size = Heap::GetFillToAlign(old_top, alignment);
   }
 
-  old_top = allocation_info_.top();
-  high = to_space_.page_high();
-  filler_size = Heap::GetFillToAlign(old_top, alignment);
-  aligned_size_in_bytes = size_in_bytes + filler_size;
-
   DCHECK(old_top + aligned_size_in_bytes <= high);
-  UpdateInlineAllocationLimit(aligned_size_in_bytes);
+
+  if (allocation_info_.limit() < high) {
+    // Either the limit has been lowered because linear allocation was disabled
+    // or because incremental marking wants to get a chance to do a step,
+    // or because idle scavenge job wants to get a chance to post a task.
+    // Set the new limit accordingly.
+    Address new_top = old_top + aligned_size_in_bytes;
+    Address soon_object = old_top + filler_size;
+    InlineAllocationStep(new_top, new_top, soon_object, size_in_bytes);
+    UpdateInlineAllocationLimit(aligned_size_in_bytes);
+  }
   return true;
 }
 
@@ -557,6 +568,12 @@ std::unique_ptr<ObjectIterator> NewSpace::GetObjectIterator(Heap* heap) {
 AllocationResult NewSpace::AllocateRawSlow(int size_in_bytes,
                                            AllocationAlignment alignment,
                                            AllocationOrigin origin) {
+  if (top() < top_on_previous_step_) {
+    // Generated code decreased the top() pointer to do folded allocations
+    DCHECK_EQ(Page::FromAllocationAreaAddress(top()),
+              Page::FromAllocationAreaAddress(top_on_previous_step_));
+    top_on_previous_step_ = top();
+  }
 #ifdef V8_HOST_ARCH_32_BIT
   return alignment != kWordAligned
              ? AllocateRawAligned(size_in_bytes, alignment, origin)
@@ -578,14 +595,8 @@ AllocationResult NewSpace::AllocateRawUnaligned(int size_in_bytes,
     return AllocationResult::Retry();
   }
 
-  DCHECK_EQ(allocation_info_.start(), allocation_info_.top());
-
   AllocationResult result = AllocateFastUnaligned(size_in_bytes, origin);
   DCHECK(!result.IsRetry());
-
-  InvokeAllocationObservers(result.ToAddress(), size_in_bytes, size_in_bytes,
-                            size_in_bytes);
-
   return result;
 }
 
@@ -596,17 +607,9 @@ AllocationResult NewSpace::AllocateRawAligned(int size_in_bytes,
     return AllocationResult::Retry();
   }
 
-  DCHECK_EQ(allocation_info_.start(), allocation_info_.top());
-
-  int aligned_size_in_bytes;
-
-  AllocationResult result = AllocateFastAligned(
-      size_in_bytes, &aligned_size_in_bytes, alignment, origin);
+  AllocationResult result =
+      AllocateFastAligned(size_in_bytes, alignment, origin);
   DCHECK(!result.IsRetry());
-
-  InvokeAllocationObservers(result.ToAddress(), size_in_bytes,
-                            aligned_size_in_bytes, aligned_size_in_bytes);
-
   return result;
 }
 

src/heap/new-spaces.h

@@ -477,8 +477,8 @@ class V8_EXPORT_PRIVATE NewSpace
 
   // Internal allocation methods.
   V8_WARN_UNUSED_RESULT V8_INLINE AllocationResult
-  AllocateFastAligned(int size_in_bytes, int* aligned_size_in_bytes,
-                      AllocationAlignment alignment, AllocationOrigin origin);
+  AllocateFastAligned(int size_in_bytes, AllocationAlignment alignment,
+                      AllocationOrigin origin);
 
   V8_WARN_UNUSED_RESULT V8_INLINE AllocationResult
   AllocateFastUnaligned(int size_in_bytes, AllocationOrigin origin);
@@ -495,7 +495,7 @@ class V8_EXPORT_PRIVATE NewSpace
       int size_in_bytes, AllocationOrigin origin = AllocationOrigin::kRuntime);
 
   bool EnsureAllocation(int size_in_bytes, AllocationAlignment alignment);
-  bool SupportsAllocationObserver() override { return true; }
+  bool SupportsInlineAllocation() override { return true; }
 
   friend class SemiSpaceObjectIterator;
 };

src/heap/paged-spaces-inl.h

@@ -6,7 +6,6 @@
 #define V8_HEAP_PAGED_SPACES_INL_H_
 
 #include "src/common/globals.h"
-#include "src/heap/heap-inl.h"
 #include "src/heap/incremental-marking.h"
 #include "src/heap/paged-spaces.h"
 #include "src/objects/code-inl.h"
@@ -97,20 +96,18 @@ bool PagedSpace::EnsureLabMain(int size_in_bytes, AllocationOrigin origin) {
   return RefillLabMain(size_in_bytes, origin);
 }
 
-AllocationResult PagedSpace::AllocateFastUnaligned(int size_in_bytes) {
+AllocationResult PagedSpace::AllocateLinearly(int size_in_bytes) {
   Address current_top = allocation_info_.top();
   Address new_top = current_top + size_in_bytes;
   if (new_top > allocation_info_.limit())
     return AllocationResult::Retry(identity());
   DCHECK_LE(new_top, allocation_info_.limit());
   allocation_info_.set_top(new_top);
-
   return AllocationResult(HeapObject::FromAddress(current_top));
 }
 
-AllocationResult PagedSpace::AllocateFastAligned(
-    int size_in_bytes, int* aligned_size_in_bytes,
-    AllocationAlignment alignment) {
+AllocationResult PagedSpace::TryAllocateLinearlyAligned(
+    int size_in_bytes, AllocationAlignment alignment) {
   Address current_top = allocation_info_.top();
   int filler_size = Heap::GetFillToAlign(current_top, alignment);
 
@@ -119,8 +116,6 @@ AllocationResult PagedSpace::AllocateFastAligned(
     return AllocationResult::Retry(identity());
 
   allocation_info_.set_top(new_top);
-  if (aligned_size_in_bytes)
-    *aligned_size_in_bytes = filler_size + size_in_bytes;
   if (filler_size > 0) {
     Heap::PrecedeWithFiller(ReadOnlyRoots(heap()),
                             HeapObject::FromAddress(current_top), filler_size);
@@ -134,8 +129,7 @@ AllocationResult PagedSpace::AllocateRawUnaligned(int size_in_bytes,
   if (!EnsureLabMain(size_in_bytes, origin)) {
     return AllocationResult::Retry(identity());
   }
-
-  AllocationResult result = AllocateFastUnaligned(size_in_bytes);
+  AllocationResult result = AllocateLinearly(size_in_bytes);
   DCHECK(!result.IsRetry());
   MSAN_ALLOCATED_UNINITIALIZED_MEMORY(result.ToObjectChecked().address(),
                                       size_in_bytes);
@@ -144,9 +138,6 @@ AllocationResult PagedSpace::AllocateRawUnaligned(int size_in_bytes,
     UpdateAllocationOrigins(origin);
   }
 
-  InvokeAllocationObservers(result.ToAddress(), size_in_bytes, size_in_bytes,
-                            size_in_bytes);
-
   return result;
 }
 
@@ -162,9 +153,8 @@ AllocationResult PagedSpace::AllocateRawAligned(int size_in_bytes,
   if (!EnsureLabMain(allocation_size, origin)) {
     return AllocationResult::Retry(identity());
   }
-  int aligned_size_in_bytes;
   AllocationResult result =
-      AllocateFastAligned(size_in_bytes, &aligned_size_in_bytes, alignment);
+      TryAllocateLinearlyAligned(size_in_bytes, alignment);
   DCHECK(!result.IsRetry());
   MSAN_ALLOCATED_UNINITIALIZED_MEMORY(result.ToObjectChecked().address(),
                                       size_in_bytes);
@@ -173,9 +163,6 @@ AllocationResult PagedSpace::AllocateRawAligned(int size_in_bytes,
     UpdateAllocationOrigins(origin);
   }
 
-  InvokeAllocationObservers(result.ToAddress(), size_in_bytes,
-                            aligned_size_in_bytes, allocation_size);
-
   return result;
 }
 
@@ -185,9 +172,9 @@ AllocationResult PagedSpace::AllocateRaw(int size_in_bytes,
   AllocationResult result;
 
   if (alignment != kWordAligned) {
-    result = AllocateFastAligned(size_in_bytes, nullptr, alignment);
+    result = TryAllocateLinearlyAligned(size_in_bytes, alignment);
   } else {
-    result = AllocateFastUnaligned(size_in_bytes);
+    result = AllocateLinearly(size_in_bytes);
   }
 
   if (!result.IsRetry()) {

src/heap/paged-spaces.cc

@@ -383,13 +383,6 @@ void PagedSpace::DecreaseLimit(Address new_limit) {
   DCHECK_LE(top(), new_limit);
   DCHECK_GE(old_limit, new_limit);
   if (new_limit != old_limit) {
-    base::Optional<CodePageMemoryModificationScope> optional_scope;
-
-    if (identity() == CODE_SPACE) {
-      MemoryChunk* chunk = MemoryChunk::FromAddress(new_limit);
-      optional_scope.emplace(chunk);
-    }
-
     SetTopAndLimit(top(), new_limit);
     Free(new_limit, old_limit - new_limit,
          SpaceAccountingMode::kSpaceAccounted);
@@ -446,7 +439,12 @@ void PagedSpace::FreeLinearAllocationArea() {
     return;
   }
 
-  AdvanceAllocationObservers();
+  if (!is_local_space()) {
+    // This can start incremental marking and mark the current
+    // linear allocation area as black. Thus destroying of the black
+    // area needs to happen afterwards.
+    InlineAllocationStep(current_top, kNullAddress, kNullAddress, 0);
+  }
 
   if (current_top != current_limit && !is_off_thread_space() &&
       heap()->incremental_marking()->black_allocation()) {
@@ -481,6 +479,7 @@ void PagedSpace::ReleasePage(Page* page) {
   free_list_->EvictFreeListItems(page);
 
   if (Page::FromAllocationAreaAddress(allocation_info_.top()) == page) {
+    DCHECK(!top_on_previous_step_);
     SetTopAndLimit(kNullAddress, kNullAddress);
   }
 
@@ -553,7 +552,6 @@ bool PagedSpace::TryAllocationFromFreeListMain(size_t size_in_bytes,
   Page* page = Page::FromHeapObject(new_node);
   IncreaseAllocatedBytes(new_node_size, page);
 
-  DCHECK_EQ(allocation_info_.start(), allocation_info_.top());
   Address start = new_node.address();
   Address end = new_node.address() + new_node_size;
   Address limit = ComputeLimit(start, end, size_in_bytes);
@@ -850,9 +848,6 @@ void PagedSpace::VerifyCountersBeforeConcurrentSweeping() {
 #endif
 
 void PagedSpace::UpdateInlineAllocationLimit(size_t min_size) {
-  // Ensure there are no unaccounted allocations.
-  DCHECK_EQ(allocation_info_.start(), allocation_info_.top());
-
   Address new_limit = ComputeLimit(top(), limit(), min_size);
   DCHECK_LE(top(), new_limit);
   DCHECK_LE(new_limit, limit());
@@ -1004,6 +999,20 @@ bool PagedSpace::ContributeToSweepingMain(int required_freed_bytes,
 AllocationResult PagedSpace::AllocateRawSlow(int size_in_bytes,
                                              AllocationAlignment alignment,
                                              AllocationOrigin origin) {
+  if (top_on_previous_step_ && top() < top_on_previous_step_ &&
+      SupportsInlineAllocation()) {
+    // Generated code decreased the top() pointer to do folded allocations.
+    // The top_on_previous_step_ can be one byte beyond the current page.
+    DCHECK_NE(top(), kNullAddress);
+    DCHECK_EQ(Page::FromAllocationAreaAddress(top()),
+              Page::FromAllocationAreaAddress(top_on_previous_step_ - 1));
+    top_on_previous_step_ = top();
+  }
+
+  size_t bytes_since_last =
+      top_on_previous_step_ ? top() - top_on_previous_step_ : 0;
+  DCHECK_IMPLIES(!SupportsInlineAllocation(), bytes_since_last == 0);
+
   if (!is_local_space()) {
     // Start incremental marking before the actual allocation, this allows the
     // allocation function to mark the object black when incremental marking is
@@ -1021,6 +1030,15 @@ AllocationResult PagedSpace::AllocateRawSlow(int size_in_bytes,
 #else
   AllocationResult result = AllocateRawUnaligned(size_in_bytes, origin);
 #endif
+  HeapObject heap_obj;
+  if (!result.IsRetry() && result.To(&heap_obj) && !is_local_space()) {
+    AllocationStep(static_cast<int>(size_in_bytes + bytes_since_last),
+                   heap_obj.address(), size_in_bytes);
+    StartNextInlineAllocationStep();
+    DCHECK_IMPLIES(
+        heap()->incremental_marking()->black_allocation(),
+        heap()->incremental_marking()->marking_state()->IsBlack(heap_obj));
+  }
   return result;
 }
 

src/heap/paged-spaces.h

@@ -317,7 +317,9 @@ class V8_EXPORT_PRIVATE PagedSpace
   void SetTopAndLimit(Address top, Address limit);
   void DecreaseLimit(Address new_limit);
   void UpdateInlineAllocationLimit(size_t min_size) override;
-  bool SupportsAllocationObserver() override { return !is_local_space(); }
+  bool SupportsInlineAllocation() override {
+    return identity() == OLD_SPACE && !is_local_space();
+  }
 
   // Slow path of allocation function
   V8_WARN_UNUSED_RESULT AllocationResult
@@ -348,14 +350,13 @@ class V8_EXPORT_PRIVATE PagedSpace
   inline bool EnsureLabMain(int size_in_bytes, AllocationOrigin origin);
   // Allocates an object from the linear allocation area. Assumes that the
   // linear allocation area is large enought to fit the object.
-  inline AllocationResult AllocateFastUnaligned(int size_in_bytes);
+  inline AllocationResult AllocateLinearly(int size_in_bytes);
   // Tries to allocate an aligned object from the linear allocation area.
   // Returns nullptr if the linear allocation area does not fit the object.
   // Otherwise, returns the object pointer and writes the allocation size
   // (object size + alignment filler size) to the size_in_bytes.
-  inline AllocationResult AllocateFastAligned(int size_in_bytes,
-                                              int* aligned_size_in_bytes,
-                                              AllocationAlignment alignment);
+  inline AllocationResult TryAllocateLinearlyAligned(
+      int size_in_bytes, AllocationAlignment alignment);
 
   V8_WARN_UNUSED_RESULT bool TryAllocationFromFreeListMain(
       size_t size_in_bytes, AllocationOrigin origin);

src/heap/spaces.cc

@@ -249,16 +249,46 @@ void Page::DestroyBlackAreaBackground(Address start, Address end) {
 
 void Space::AddAllocationObserver(AllocationObserver* observer) {
   allocation_counter_.AddAllocationObserver(observer);
+  StartNextInlineAllocationStep();
 }
 
 void Space::RemoveAllocationObserver(AllocationObserver* observer) {
   allocation_counter_.RemoveAllocationObserver(observer);
+  StartNextInlineAllocationStep();
 }
 
 void Space::PauseAllocationObservers() { allocation_counter_.Pause(); }
 
 void Space::ResumeAllocationObservers() { allocation_counter_.Resume(); }
 
+void Space::AllocationStep(int bytes_since_last, Address soon_object,
+                           int size) {
+  if (!allocation_counter_.IsActive()) {
+    return;
+  }
+
+  DCHECK(!heap()->allocation_step_in_progress());
+  heap()->set_allocation_step_in_progress(true);
+  heap()->CreateFillerObjectAt(soon_object, size, ClearRecordedSlots::kNo);
+  for (AllocationObserver* observer : allocation_counter_) {
+    observer->AllocationStep(bytes_since_last, soon_object, size);
+  }
+  heap()->set_allocation_step_in_progress(false);
+}
+
+void Space::AllocationStepAfterMerge(Address first_object_in_chunk, int size) {
+  if (!allocation_counter_.IsActive()) {
+    return;
+  }
+
+  DCHECK(!heap()->allocation_step_in_progress());
+  heap()->set_allocation_step_in_progress(true);
+  for (AllocationObserver* observer : allocation_counter_) {
+    observer->AllocationStep(size, first_object_in_chunk, size);
+  }
+  heap()->set_allocation_step_in_progress(false);
+}
+
 Address SpaceWithLinearArea::ComputeLimit(Address start, Address end,
                                           size_t min_size) {
   DCHECK_GE(end - start, min_size);
@@ -266,19 +296,14 @@ Address SpaceWithLinearArea::ComputeLimit(Address start, Address end,
   if (heap()->inline_allocation_disabled()) {
     // Fit the requested area exactly.
     return start + min_size;
-  } else if (SupportsAllocationObserver() && allocation_counter_.IsActive()) {
-    // Ensure there are no unaccounted allocations.
-    DCHECK_EQ(allocation_info_.start(), allocation_info_.top());
-
+  } else if (SupportsInlineAllocation() && allocation_counter_.IsActive()) {
     // Generated code may allocate inline from the linear allocation area for.
-    // To make sure we can observe these allocations, we use a lower ©limit.
-    size_t step = allocation_counter_.NextBytes();
-    DCHECK_NE(step, 0);
+    // To make sure we can observe these allocations, we use a lower limit.
+    size_t step = allocation_counter_.GetNextInlineAllocationStepSize();
     size_t rounded_step =
         RoundSizeDownToObjectAlignment(static_cast<int>(step - 1));
     // Use uint64_t to avoid overflow on 32-bit
-    uint64_t step_end =
-        static_cast<uint64_t>(start) + Max(min_size, rounded_step);
+    uint64_t step_end = static_cast<uint64_t>(start) + min_size + rounded_step;
     uint64_t new_end = Min(step_end, static_cast<uint64_t>(end));
     return static_cast<Address>(new_end);
   } else {
@@ -345,75 +370,74 @@ LocalAllocationBuffer& LocalAllocationBuffer::operator=(
   other.allocation_info_.Reset(kNullAddress, kNullAddress);
   return *this;
 }
+void SpaceWithLinearArea::StartNextInlineAllocationStep() {
+  if (heap()->allocation_step_in_progress()) {
+    // If we are mid-way through an existing step, don't start a new one.
+    return;
+  }
+
+  if (allocation_counter_.IsActive()) {
+    top_on_previous_step_ = top();
+    UpdateInlineAllocationLimit(0);
+  } else {
+    DCHECK_EQ(kNullAddress, top_on_previous_step_);
+  }
+}
 
 void SpaceWithLinearArea::AddAllocationObserver(AllocationObserver* observer) {
-  AdvanceAllocationObservers();
+  InlineAllocationStep(top(), top(), kNullAddress, 0);
   Space::AddAllocationObserver(observer);
-  UpdateInlineAllocationLimit(0);
+  DCHECK_IMPLIES(top_on_previous_step_, allocation_counter_.IsActive());
 }
 
 void SpaceWithLinearArea::RemoveAllocationObserver(
     AllocationObserver* observer) {
-  AdvanceAllocationObservers();
+  Address top_for_next_step =
+      allocation_counter_.NumberAllocationObservers() == 1 ? kNullAddress
+                                                           : top();
+  InlineAllocationStep(top(), top_for_next_step, kNullAddress, 0);
   Space::RemoveAllocationObserver(observer);
-  UpdateInlineAllocationLimit(0);
+  DCHECK_IMPLIES(top_on_previous_step_, allocation_counter_.IsActive());
 }
 
 void SpaceWithLinearArea::PauseAllocationObservers() {
-  AdvanceAllocationObservers();
+  // Do a step to account for memory allocated so far.
+  InlineAllocationStep(top(), kNullAddress, kNullAddress, 0);
   Space::PauseAllocationObservers();
+  DCHECK_EQ(kNullAddress, top_on_previous_step_);
+  UpdateInlineAllocationLimit(0);
 }
 
 void SpaceWithLinearArea::ResumeAllocationObservers() {
+  DCHECK_EQ(kNullAddress, top_on_previous_step_);
   Space::ResumeAllocationObservers();
-  allocation_info_.MoveStartToTop();
-  UpdateInlineAllocationLimit(0);
+  StartNextInlineAllocationStep();
 }
 
-void SpaceWithLinearArea::AdvanceAllocationObservers() {
-  if (allocation_info_.top()) {
-    allocation_counter_.AdvanceAllocationObservers(allocation_info_.top() -
-                                                   allocation_info_.start());
-    allocation_info_.MoveStartToTop();
+void SpaceWithLinearArea::InlineAllocationStep(Address top,
+                                               Address top_for_next_step,
+                                               Address soon_object,
+                                               size_t size) {
+  if (heap()->allocation_step_in_progress()) {
+    // Avoid starting a new step if we are mid-way through an existing one.
+    return;
   }
-}
 
-// Perform an allocation step when the step is reached. size_in_bytes is the
-// actual size needed for the object (required for InvokeAllocationObservers).
-// aligned_size_in_bytes is the size of the object including the filler right
-// before it to reach the right alignment (required to DCHECK the start of the
-// object). allocation_size is the size of the actual allocation which needs to
-// be used for the accounting. It can be different from aligned_size_in_bytes in
-// PagedSpace::AllocateRawAligned, where we have to overallocate in order to be
-// able to align the allocation afterwards.
-void SpaceWithLinearArea::InvokeAllocationObservers(
-    Address soon_object, size_t size_in_bytes, size_t aligned_size_in_bytes,
-    size_t allocation_size) {
-  DCHECK_LE(size_in_bytes, aligned_size_in_bytes);
-  DCHECK_LE(aligned_size_in_bytes, allocation_size);
-  DCHECK(size_in_bytes == aligned_size_in_bytes ||
-         aligned_size_in_bytes == allocation_size);
-
-  if (!SupportsAllocationObserver() || !allocation_counter_.IsActive()) return;
-
-  if (allocation_size >= allocation_counter_.NextBytes()) {
-    // Only the first object in a LAB should reach the next step.
-    DCHECK_EQ(soon_object,
-              allocation_info_.start() + aligned_size_in_bytes - size_in_bytes);
-
-    // Ensure that there is a valid object
-    heap_->CreateFillerObjectAt(soon_object, static_cast<int>(size_in_bytes),
-                                ClearRecordedSlots::kNo);
-
-    // Run AllocationObserver::Step through the AllocationCounter.
-    allocation_counter_.InvokeAllocationObservers(soon_object, size_in_bytes,
-                                                  allocation_size);
+  if (top_on_previous_step_) {
+    if (top < top_on_previous_step_) {
+      // Generated code decreased the top pointer to do folded allocations.
+      DCHECK_NE(top, kNullAddress);
+      DCHECK_EQ(Page::FromAllocationAreaAddress(top),
+                Page::FromAllocationAreaAddress(top_on_previous_step_));
+      top_on_previous_step_ = top;
+    }
+    int bytes_allocated = static_cast<int>(top - top_on_previous_step_);
+    AllocationStep(bytes_allocated, soon_object, static_cast<int>(size));
+    top_on_previous_step_ = top_for_next_step;
   }
-
-  DCHECK_LT(allocation_info_.limit() - allocation_info_.start(),
-            allocation_counter_.NextBytes());
 }
 
+
 int MemoryChunk::FreeListsLength() {
   int length = 0;
   for (int cat = kFirstCategory; cat <= owner()->free_list()->last_category();

src/heap/spaces.h

@@ -112,6 +112,7 @@ class V8_EXPORT_PRIVATE Space : public BaseSpace {
  public:
   Space(Heap* heap, AllocationSpace id, FreeList* free_list)
       : BaseSpace(heap, id),
+        allocation_counter_(heap),
         free_list_(std::unique_ptr<FreeList>(free_list)) {
     external_backing_store_bytes_ =
         new std::atomic<size_t>[ExternalBackingStoreType::kNumTypes];
@@ -138,6 +139,13 @@ class V8_EXPORT_PRIVATE Space : public BaseSpace {
 
   virtual void StartNextInlineAllocationStep() {}
 
+  void AllocationStep(int bytes_since_last, Address soon_object, int size);
+
+  // An AllocationStep equivalent to be called after merging a contiguous
+  // chunk of an off-thread space into this space. The chunk is treated as a
+  // single allocation-folding group.
+  void AllocationStepAfterMerge(Address first_object_in_chunk, int size);
+
   // Returns size of objects. Can differ from the allocated size
   // (e.g. see OldLargeObjectSpace).
   virtual size_t SizeOfObjects() { return Size(); }
@@ -373,8 +381,6 @@ class LinearAllocationArea {
     set_limit(limit);
   }
 
-  void MoveStartToTop() { start_ = top_; }
-
   V8_INLINE Address start() const { return start_; }
 
   V8_INLINE void set_top(Address top) {
@@ -484,11 +490,11 @@ class LocalAllocationBuffer {
 class SpaceWithLinearArea : public Space {
  public:
   SpaceWithLinearArea(Heap* heap, AllocationSpace id, FreeList* free_list)
-      : Space(heap, id, free_list) {
+      : Space(heap, id, free_list), top_on_previous_step_(0) {
     allocation_info_.Reset(kNullAddress, kNullAddress);
   }
 
-  virtual bool SupportsAllocationObserver() = 0;
+  virtual bool SupportsInlineAllocation() = 0;
 
   // Returns the allocation pointer in this space.
   Address top() { return allocation_info_.top(); }
@@ -502,7 +508,6 @@ class SpaceWithLinearArea : public Space {
     return allocation_info_.limit_address();
   }
 
-  // Methods needed for allocation observers.
   V8_EXPORT_PRIVATE void AddAllocationObserver(
       AllocationObserver* observer) override;
   V8_EXPORT_PRIVATE void RemoveAllocationObserver(
@@ -510,12 +515,6 @@ class SpaceWithLinearArea : public Space {
   V8_EXPORT_PRIVATE void ResumeAllocationObservers() override;
   V8_EXPORT_PRIVATE void PauseAllocationObservers() override;
 
-  V8_EXPORT_PRIVATE void AdvanceAllocationObservers();
-  V8_EXPORT_PRIVATE void InvokeAllocationObservers(Address soon_object,
-                                                   size_t size_in_bytes,
-                                                   size_t aligned_size_in_bytes,
-                                                   size_t allocation_size);
-
   // When allocation observers are active we may use a lower limit to allow the
   // observers to 'interrupt' earlier than the natural limit. Given a linear
   // area bounded by [start, end), this function computes the limit to use to
@@ -530,8 +529,22 @@ class SpaceWithLinearArea : public Space {
   void PrintAllocationsOrigins();
 
  protected:
+  // If we are doing inline allocation in steps, this method performs the 'step'
+  // operation. top is the memory address of the bump pointer at the last
+  // inline allocation (i.e. it determines the numbers of bytes actually
+  // allocated since the last step.) top_for_next_step is the address of the
+  // bump pointer where the next byte is going to be allocated from. top and
+  // top_for_next_step may be different when we cross a page boundary or reset
+  // the space.
+  // TODO(ofrobots): clarify the precise difference between this and
+  // Space::AllocationStep.
+  void InlineAllocationStep(Address top, Address top_for_next_step,
+                            Address soon_object, size_t size);
+  V8_EXPORT_PRIVATE void StartNextInlineAllocationStep() override;
+
   // TODO(ofrobots): make these private after refactoring is complete.
   LinearAllocationArea allocation_info_;
+  Address top_on_previous_step_;
 
   size_t allocations_origins_[static_cast<int>(
       AllocationOrigin::kNumberOfAllocationOrigins)] = {0};

test/unittests/BUILD.gn

@@ -232,7 +232,6 @@ v8_source_set("unittests_sources") {
     "diagnostics/eh-frame-iterator-unittest.cc",
     "diagnostics/eh-frame-writer-unittest.cc",
     "execution/microtask-queue-unittest.cc",
-    "heap/allocation-observer-unittest.cc",
     "heap/barrier-unittest.cc",
     "heap/bitmap-test-utils.h",
     "heap/bitmap-unittest.cc",

test/unittests/heap/allocation-observer-unittest.cc

-// Copyright 2020 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.
-
-#include "src/heap/allocation-observer.h"
-
-#include "src/base/logging.h"
-#include "test/unittests/test-utils.h"
-#include "testing/gtest/include/gtest/gtest.h"
-
-namespace v8 {
-namespace internal {
-
-namespace {
-class UnusedObserver : public AllocationObserver {
- public:
-  explicit UnusedObserver(size_t step_size) : AllocationObserver(step_size) {}
-  void Step(int bytes_allocated, Address soon_object, size_t size) override {
-    CHECK(false);
-  }
-};
-}  // namespace
-
-TEST(AllocationObserverTest, AddAndRemoveUnusedObservers) {
-  AllocationCounter counter;
-  CHECK(!counter.IsActive());
-
-  UnusedObserver observer100(100);
-  UnusedObserver observer200(200);
-
-  counter.AddAllocationObserver(&observer200);
-  CHECK_EQ(counter.NextBytes(), 200);
-
-  counter.AddAllocationObserver(&observer100);
-  CHECK_EQ(counter.NextBytes(), 100);
-
-  counter.AdvanceAllocationObservers(90);
-  CHECK_EQ(counter.NextBytes(), 10);
-
-  counter.RemoveAllocationObserver(&observer100);
-  CHECK_EQ(counter.NextBytes(), 110);
-
-  counter.RemoveAllocationObserver(&observer200);
-  CHECK(!counter.IsActive());
-}
-
-namespace {
-class VerifyStepObserver : public AllocationObserver {
- public:
-  explicit VerifyStepObserver(size_t step_size)
-      : AllocationObserver(step_size) {}
-
-  void Step(int bytes_allocated, Address soon_object, size_t size) override {
-    CHECK(!do_not_invoke_);
-
-    invocations_++;
-    CHECK_EQ(expected_bytes_allocated_, bytes_allocated);
-    CHECK_EQ(expected_size_, size);
-  }
-
-  void ExpectNoInvocation() { do_not_invoke_ = true; }
-  void Expect(int expected_bytes_allocated, size_t expected_size) {
-    do_not_invoke_ = false;
-    expected_bytes_allocated_ = expected_bytes_allocated;
-    expected_size_ = expected_size;
-  }
-
-  int Invocations() { return invocations_; }
-
- private:
-  bool do_not_invoke_ = false;
-  int invocations_ = 0;
-  int expected_bytes_allocated_ = 0;
-  size_t expected_size_ = 0;
-};
-}  // namespace
-
-TEST(AllocationObserverTest, Step) {
-  AllocationCounter counter;
-  CHECK(!counter.IsActive());
-  const Address kSomeObjectAddress = 8;
-
-  VerifyStepObserver observer100(100);
-  VerifyStepObserver observer200(200);
-
-  counter.AddAllocationObserver(&observer100);
-  counter.AddAllocationObserver(&observer200);
-
-  observer100.Expect(90, 8);
-  observer200.ExpectNoInvocation();
-
-  counter.AdvanceAllocationObservers(90);
-  counter.InvokeAllocationObservers(kSomeObjectAddress, 8, 10);
-  CHECK_EQ(observer100.Invocations(), 1);
-  CHECK_EQ(observer200.Invocations(), 0);
-  CHECK_EQ(counter.NextBytes(),
-           10 /* aligned_object_size */ + 100 /* smallest step size*/);
-
-  observer100.Expect(90, 16);
-  observer200.Expect(180, 16);
-
-  counter.AdvanceAllocationObservers(90);
-  counter.InvokeAllocationObservers(kSomeObjectAddress, 16, 20);
-  CHECK_EQ(observer100.Invocations(), 2);
-  CHECK_EQ(observer200.Invocations(), 1);
-  CHECK_EQ(counter.NextBytes(),
-           20 /* aligned_object_size */ + 100 /* smallest step size*/);
-}
-
-}  // namespace internal
-}  // namespace v8