[heap] Remove border page

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 8982a2953273abbe35993b57ab63ee43d42ae0d7..db3525d8db25a53f175c74845e412711d9f2b3da 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -1484,8 +1484,9 @@ 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);
@@ -1586,8 +1587,16 @@ 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());

[Hannes Payer (out of office), 2016/09/27 08:28:31]

can we set top and limit to null?

[Michael Lippautz, 2016/09/27 11:13:47]

As discussed offline, there are quite some callers that expect top() to be
non-null (e.g. accounting, iterating page ranges, ...).

+        }
         to_remove->Unlink();
         heap()->memory_allocator()->Free<MemoryAllocator::kPooledAndQueue>(
             to_remove);
@@ -1913,9 +1922,6 @@ bool SemiSpace::Commit() {
   }
   Reset();
   AccountCommitted(current_capacity_);
-  if (age_mark_ == nullptr) {
-    age_mark_ = first_page()->area_start();
-  }
   committed_ = true;
   return true;
 }
@@ -2027,7 +2033,7 @@ 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);
@@ -2070,7 +2076,6 @@ 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_);
@@ -2079,16 +2084,33 @@ void SemiSpace::Swap(SemiSpace* from, SemiSpace* to) {
   from->FixPagesFlags(0, 0);
 }
 
+void NewSpace::SealIntermediateGeneration() {
+  fragmentation_in_intermediate_generation_ = 0;
+  const Address mark = top();
 
-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());

[Hannes Payer (out of office), 2016/09/27 08:28:31]

same as above, wouldn't it be cleaner to set top and limit to null here?

[Michael Lippautz, 2016/09/27 11:13:47]

See above.

+    }
+  }
+  if (FLAG_trace_gc_verbose) {
+    PrintIsolate(heap()->isolate(),
+                 "Sealing intermediate generation: bytes_lost=%zu\n",
+                 fragmentation_in_intermediate_generation_);
+  }
+}
 
 #ifdef DEBUG
 void SemiSpace::Print() {}