[heap] Remove border page

A page now belongs either the nursery *or* the intermediate gen. The page that
contained objects of both spaces is removed in this change.

BUG=chromium:636331

Review-Url: https://codereview.chromium.org/2209583002
Cr-Commit-Position: refs/heads/master@{#39778}

src/heap/heap-inl.h

@@ -519,9 +519,6 @@ bool Heap::OldGenerationAllocationLimitReached() {
 
 template <PromotionMode promotion_mode>
 bool Heap::ShouldBePromoted(Address old_address, int object_size) {
-  Page* page = Page::FromAddress(old_address);
-  Address age_mark = new_space_->age_mark();
-
   if (promotion_mode == PROMOTE_MARKED) {
     MarkBit mark_bit = ObjectMarking::MarkBitFrom(old_address);
     if (!Marking::IsWhite(mark_bit)) {
@@ -529,8 +526,7 @@ bool Heap::ShouldBePromoted(Address old_address, int object_size) {
     }
   }
 
-  return page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK) &&
-         (!page->ContainsLimit(age_mark) || old_address < age_mark);
+  return Page::FromAddress(old_address)->InIntermediateGeneration();
 }
 
 PromotionMode Heap::CurrentPromotionMode() {
@@ -631,16 +627,8 @@ AllocationMemento* Heap::FindAllocationMemento(HeapObject* object) {
   // Bail out if the memento is below the age mark, which can happen when
   // mementos survived because a page got moved within new space.
   Page* object_page = Page::FromAddress(object_address);
-  if (object_page->IsFlagSet(Page::NEW_SPACE_BELOW_AGE_MARK)) {
-    Address age_mark =
-        reinterpret_cast<SemiSpace*>(object_page->owner())->age_mark();
-    if (!object_page->Contains(age_mark)) {
-      return nullptr;
-    }
-    // Do an exact check in the case where the age mark is on the same page.
-    if (object_address < age_mark) {
-      return nullptr;
-    }
+  if (object_page->InIntermediateGeneration()) {
+    return nullptr;
   }
 
   AllocationMemento* memento_candidate = AllocationMemento::cast(candidate);

src/heap/heap.cc

@@ -1755,8 +1755,7 @@ void Heap::Scavenge() {
 
   DCHECK(new_space_front == new_space_->top());
 
-  // Set age mark.
-  new_space_->set_age_mark(new_space_->top());
+  new_space_->SealIntermediateGeneration();
 
   ArrayBufferTracker::FreeDeadInNewSpace(this);
 
@@ -5107,7 +5106,6 @@ bool Heap::ConfigureHeap(int max_semi_space_size, int max_old_space_size,
   }
 
   initial_semispace_size_ = Min(initial_semispace_size_, max_semi_space_size_);
-
   if (FLAG_semi_space_growth_factor < 2) {
     FLAG_semi_space_growth_factor = 2;
   }

src/heap/heap.h

@@ -1364,7 +1364,6 @@ class Heap {
   }
 
   inline void UpdateNewSpaceAllocationCounter();
-
   inline size_t NewSpaceAllocationCounter();
 
   // This should be used only for testing.

src/heap/mark-compact.cc

@@ -3188,15 +3188,13 @@ bool MarkCompactCollector::Evacuator::EvacuatePage(Page* page) {
   if (FLAG_trace_evacuation) {
     PrintIsolate(heap->isolate(),
                  "evacuation[%p]: page=%p new_space=%d "
-                 "page_evacuation=%d executable=%d contains_age_mark=%d "
-                 "live_bytes=%d time=%f\n",
+                 "page_evacuation=%d executable=%d live_bytes=%d time=%f\n",
                  static_cast<void*>(this), static_cast<void*>(page),
                  page->InNewSpace(),
                  page->IsFlagSet(Page::PAGE_NEW_OLD_PROMOTION) ||
                      page->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION),
-                 page->IsFlagSet(MemoryChunk::IS_EXECUTABLE),
-                 page->Contains(heap->new_space()->age_mark()),
-                 saved_live_bytes, evacuation_time);
+                 page->IsFlagSet(MemoryChunk::IS_EXECUTABLE), saved_live_bytes,
+                 evacuation_time);
   }
   return success;
 }
@@ -3306,13 +3304,11 @@ void MarkCompactCollector::EvacuatePagesInParallel() {
     job.AddPage(page, &abandoned_pages);
   }
 
-  const Address age_mark = heap()->new_space()->age_mark();
   for (Page* page : newspace_evacuation_candidates_) {
     live_bytes += page->LiveBytes();
     if (!page->NeverEvacuate() &&
-        (page->LiveBytes() > Evacuator::PageEvacuationThreshold()) &&
-        !page->Contains(age_mark)) {
-      if (page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK)) {
+        (page->LiveBytes() > Evacuator::PageEvacuationThreshold())) {
+      if (page->InIntermediateGeneration()) {
         EvacuateNewSpacePageVisitor::MoveToOldSpace(page, heap()->old_space());
       } else {
         EvacuateNewSpacePageVisitor::MoveToToSpace(page);
@@ -3558,7 +3554,7 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
 
     EvacuateNewSpacePrologue();
     EvacuatePagesInParallel();
-    heap()->new_space()->set_age_mark(heap()->new_space()->top());
+    heap()->new_space()->SealIntermediateGeneration();
   }
 
   UpdatePointersAfterEvacuation();

src/heap/spaces-inl.h

@@ -165,6 +165,22 @@ bool NewSpace::FromSpaceContainsSlow(Address a) {
 bool NewSpace::ToSpaceContains(Object* o) { return to_space_.Contains(o); }
 bool NewSpace::FromSpaceContains(Object* o) { return from_space_.Contains(o); }
 
+size_t NewSpace::AllocatedSinceLastGC() {
+  Page* top_page = Page::FromAllocationAreaAddress(top());
+  size_t allocated = 0;
+  // If top gets reset to be in the range of pages that are below the age
+  // mark, this loop will not trigger and we return 0 (invalid).
+  for (Page* current_page = top_page;
+       !current_page->InIntermediateGeneration() &&
+       current_page != to_space_.anchor();
+       current_page = current_page->prev_page()) {
+    allocated += (top_page == current_page)
+                     ? static_cast<size_t>(top() - current_page->area_start())
+                     : Page::kAllocatableMemory;
+  }
+  return allocated;
+}
+
 // --------------------------------------------------------------------------
 // AllocationResult
 

src/heap/spaces.cc

@@ -1485,8 +1485,9 @@ void PagedSpace::Verify(ObjectVisitor* visitor) {
 
 bool NewSpace::SetUp(int initial_semispace_capacity,
                      int maximum_semispace_capacity) {
-  DCHECK(initial_semispace_capacity <= maximum_semispace_capacity);
+  DCHECK_LE(initial_semispace_capacity, maximum_semispace_capacity);
   DCHECK(base::bits::IsPowerOfTwo32(maximum_semispace_capacity));
+  DCHECK_GE(initial_semispace_capacity, 2 * Page::kPageSize);
 
   to_space_.SetUp(initial_semispace_capacity, maximum_semispace_capacity);
   from_space_.SetUp(initial_semispace_capacity, maximum_semispace_capacity);
@@ -1587,8 +1588,16 @@ bool SemiSpace::EnsureCurrentCapacity() {
       current_page = current_page->next_page();
       if (actual_pages > expected_pages) {
         Page* to_remove = current_page->prev_page();
-        // Make sure we don't overtake the actual top pointer.
-        CHECK_NE(to_remove, current_page_);
+        if (to_remove == current_page_) {
+          // Corner case: All pages have been moved within new space. We are
+          // removing the page that contains the top pointer and need to set
+          // it to the end of the intermediate generation.
+          NewSpace* new_space = heap()->new_space();
+          CHECK_EQ(new_space->top(), current_page_->area_start());
+          current_page_ = to_remove->prev_page();
+          CHECK(current_page_->InIntermediateGeneration());
+          new_space->SetAllocationInfo(page_high(), page_high());
+        }
         to_remove->Unlink();
         heap()->memory_allocator()->Free<MemoryAllocator::kPooledAndQueue>(
             to_remove);
@@ -1914,9 +1923,6 @@ bool SemiSpace::Commit() {
   }
   Reset();
   AccountCommitted(current_capacity_);
-  if (age_mark_ == nullptr) {
-    age_mark_ = first_page()->area_start();
-  }
   committed_ = true;
   return true;
 }
@@ -2028,7 +2034,7 @@ void SemiSpace::FixPagesFlags(intptr_t flags, intptr_t mask) {
     if (id_ == kToSpace) {
       page->ClearFlag(MemoryChunk::IN_FROM_SPACE);
       page->SetFlag(MemoryChunk::IN_TO_SPACE);
-      page->ClearFlag(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK);
+      page->ClearFlag(MemoryChunk::IN_INTERMEDIATE_GENERATION);
       page->ResetLiveBytes();
     } else {
       page->SetFlag(MemoryChunk::IN_FROM_SPACE);
@@ -2071,7 +2077,6 @@ void SemiSpace::Swap(SemiSpace* from, SemiSpace* to) {
   std::swap(from->current_capacity_, to->current_capacity_);
   std::swap(from->maximum_capacity_, to->maximum_capacity_);
   std::swap(from->minimum_capacity_, to->minimum_capacity_);
-  std::swap(from->age_mark_, to->age_mark_);
   std::swap(from->committed_, to->committed_);
   std::swap(from->anchor_, to->anchor_);
   std::swap(from->current_page_, to->current_page_);
@@ -2080,16 +2085,39 @@ void SemiSpace::Swap(SemiSpace* from, SemiSpace* to) {
   from->FixPagesFlags(0, 0);
 }
 
+void NewSpace::SealIntermediateGeneration() {
+  fragmentation_in_intermediate_generation_ = 0;
+  const Address mark = top();
+
+  if (mark == to_space_.space_start()) {
+    // Do not mark any pages as being part of the intermediate generation if no
+    // objects got moved.
+    return;
+  }
 
-void SemiSpace::set_age_mark(Address mark) {
-  DCHECK_EQ(Page::FromAllocationAreaAddress(mark)->owner(), this);
-  age_mark_ = mark;
-  // Mark all pages up to the one containing mark.
-  for (Page* p : NewSpacePageRange(space_start(), mark)) {
-    p->SetFlag(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK);
+  for (Page* p : NewSpacePageRange(to_space_.space_start(), mark)) {
+    p->SetFlag(MemoryChunk::IN_INTERMEDIATE_GENERATION);
   }
-}
 
+  Page* p = Page::FromAllocationAreaAddress(mark);
+  if (mark < p->area_end()) {
+    heap()->CreateFillerObjectAt(mark, static_cast<int>(p->area_end() - mark),
+                                 ClearRecordedSlots::kNo);
+    fragmentation_in_intermediate_generation_ =
+        static_cast<size_t>(p->area_end() - mark);
+    DCHECK_EQ(to_space_.current_page(), p);
+    if (to_space_.AdvancePage()) {
+      UpdateAllocationInfo();
+    } else {
+      allocation_info_.Reset(to_space_.page_high(), to_space_.page_high());
+    }
+  }
+  if (FLAG_trace_gc_verbose) {
+    PrintIsolate(heap()->isolate(),
+                 "Sealing intermediate generation: bytes_lost=%zu\n",
+                 fragmentation_in_intermediate_generation_);
+  }
+}
 
 #ifdef DEBUG
 void SemiSpace::Print() {}

src/heap/spaces.h

@@ -234,10 +234,14 @@ class MemoryChunk {
     IS_EXECUTABLE = 1u << 0,
     POINTERS_TO_HERE_ARE_INTERESTING = 1u << 1,
     POINTERS_FROM_HERE_ARE_INTERESTING = 1u << 2,
+
     // A page in new space has one of the next to flags set.
     IN_FROM_SPACE = 1u << 3,
     IN_TO_SPACE = 1u << 4,
-    NEW_SPACE_BELOW_AGE_MARK = 1u << 5,
+    // |IN_INTERMEDIATE_GENERATION|: Flag indicates whether this page contains
+    // objects that have already been copied once.
+    IN_INTERMEDIATE_GENERATION = 1u << 5,
+
     EVACUATION_CANDIDATE = 1u << 6,
     NEVER_EVACUATE = 1u << 7,
 
@@ -559,6 +563,10 @@ class MemoryChunk {
 
   bool InFromSpace() { return IsFlagSet(IN_FROM_SPACE); }
 
+  bool InIntermediateGeneration() {
+    return IsFlagSet(IN_INTERMEDIATE_GENERATION);
+  }
+
   MemoryChunk* next_chunk() { return next_chunk_.Value(); }
 
   MemoryChunk* prev_chunk() { return prev_chunk_.Value(); }
@@ -2224,7 +2232,6 @@ class SemiSpace : public Space {
         current_capacity_(0),
         maximum_capacity_(0),
         minimum_capacity_(0),
-        age_mark_(nullptr),
         committed_(false),
         id_(semispace),
         anchor_(this),
@@ -2293,10 +2300,6 @@ class SemiSpace : public Space {
   void RemovePage(Page* page);
   void PrependPage(Page* page);
 
-  // Age mark accessors.
-  Address age_mark() { return age_mark_; }
-  void set_age_mark(Address mark);
-
   // Returns the current capacity of the semispace.
   int current_capacity() { return current_capacity_; }
 
@@ -2363,9 +2366,6 @@ class SemiSpace : public Space {
   // The minimum capacity for the space. A space cannot shrink below this size.
   int minimum_capacity_;
 
-  // Used to govern object promotion during mark-compact collection.
-  Address age_mark_;
-
   bool committed_;
   SemiSpaceId id_;
 
@@ -2416,7 +2416,8 @@ class NewSpace : public Space {
         reservation_(),
         top_on_previous_step_(0),
         allocated_histogram_(nullptr),
-        promoted_histogram_(nullptr) {}
+        promoted_histogram_(nullptr),
+        fragmentation_in_intermediate_generation_(0) {}
 
   inline bool Contains(HeapObject* o);
   inline bool ContainsSlow(Address a);
@@ -2449,6 +2450,11 @@ class NewSpace : public Space {
            static_cast<int>(top() - to_space_.page_low());
   }
 
+  intptr_t SizeOfObjects() override {
+    return Size() -
+           static_cast<intptr_t>(fragmentation_in_intermediate_generation_);
+  }
+
   // The same, but returning an int.  We have to have the one that returns
   // intptr_t because it is inherited, but if we know we are dealing with the
   // new space, which can't get as big as the other spaces then this is useful:
@@ -2485,42 +2491,7 @@ class NewSpace : public Space {
   // Return the available bytes without growing.
   intptr_t Available() override { return Capacity() - Size(); }
 
-  size_t AllocatedSinceLastGC() {
-    bool seen_age_mark = false;
-    Address age_mark = to_space_.age_mark();
-    Page* current_page = to_space_.first_page();
-    Page* age_mark_page = Page::FromAddress(age_mark);
-    Page* last_page = Page::FromAddress(top() - kPointerSize);
-    if (age_mark_page == last_page) {
-      if (top() - age_mark >= 0) {
-        return top() - age_mark;
-      }
-      // Top was reset at some point, invalidating this metric.
-      return 0;
-    }
-    while (current_page != last_page) {
-      if (current_page == age_mark_page) {
-        seen_age_mark = true;
-        break;
-      }
-      current_page = current_page->next_page();
-    }
-    if (!seen_age_mark) {
-      // Top was reset at some point, invalidating this metric.
-      return 0;
-    }
-    intptr_t allocated = age_mark_page->area_end() - age_mark;
-    DCHECK_EQ(current_page, age_mark_page);
-    current_page = age_mark_page->next_page();
-    while (current_page != last_page) {
-      allocated += Page::kAllocatableMemory;
-      current_page = current_page->next_page();
-    }
-    allocated += top() - current_page->area_start();
-    DCHECK_LE(0, allocated);
-    DCHECK_LE(allocated, Size());
-    return static_cast<size_t>(allocated);
-  }
+  inline size_t AllocatedSinceLastGC();
 
   void MovePageFromSpaceToSpace(Page* page) {
     DCHECK(page->InFromSpace());
@@ -2559,10 +2530,8 @@ class NewSpace : public Space {
   // Return the address of the first object in the active semispace.
   Address bottom() { return to_space_.space_start(); }
 
-  // Get the age mark of the inactive semispace.
-  Address age_mark() { return from_space_.age_mark(); }
-  // Set the age mark in the active semispace.
-  void set_age_mark(Address mark) { to_space_.set_age_mark(mark); }
+  // Seal the intermediate generation of the active semispace.
+  void SealIntermediateGeneration();
 
   // The allocation top and limit address.
   Address* allocation_top_address() { return allocation_info_.top_address(); }
@@ -2587,6 +2556,10 @@ class NewSpace : public Space {
   // Reset the allocation pointer to the beginning of the active semispace.
   void ResetAllocationInfo();
 
+  void SetAllocationInfo(Address top, Address limit) {
+    allocation_info_.Reset(top, limit);
+  }
+
   // When inline allocation stepping is active, either because of incremental
   // marking, idle scavenge, or allocation statistics gathering, we 'interrupt'
   // inline allocation every once in a while. This is done by setting
@@ -2695,6 +2668,8 @@ class NewSpace : public Space {
   HistogramInfo* allocated_histogram_;
   HistogramInfo* promoted_histogram_;
 
+  size_t fragmentation_in_intermediate_generation_;
+
   bool EnsureAllocation(int size_in_bytes, AllocationAlignment alignment);
 
   // If we are doing inline allocation in steps, this method performs the 'step'

test/cctest/heap/test-heap.cc

@@ -7110,5 +7110,20 @@ TEST(RememberedSetRemoveRange) {
   });
 }
 
+TEST(EmptyIntermediateGeneration) {
+  CcTest::InitializeVM();
+  Heap* heap = CcTest::heap();
+  heap::GcAndSweep(heap, OLD_SPACE);
+  v8::HandleScope scope(CcTest::isolate());
+  {
+    v8::HandleScope temp_scope(CcTest::isolate());
+    heap::SimulateFullSpace(heap->new_space());
+  }
+  heap::GcAndSweep(heap, OLD_SPACE);
+  for (Page* p : *heap->new_space()) {
+    CHECK(!p->InIntermediateGeneration());
+  }
+}
+
 }  // namespace internal
 }  // namespace v8