[heap] Uncommit unused large object page memory.

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 332d59114b2c601b2a27ae1ac21eb8557d3ac00c..4a565ac90747bea2c3f4bc4e15af1386ec13d778 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -584,6 +584,11 @@ bool MemoryChunk::CommitArea(size_t requested) {
   return true;
 }
 
+size_t MemoryChunk::CommittedPhysicalMemory() {
+  if (!base::VirtualMemory::HasLazyCommits() || owner()->identity() == LO_SPACE)
+    return size();
+  return high_water_mark_.Value();
+}
 
 void MemoryChunk::InsertAfter(MemoryChunk* other) {
   MemoryChunk* other_next = other->next_chunk();
@@ -751,6 +756,27 @@ void Page::ResetFreeListStatistics() {
   available_in_free_list_ = 0;
 }
 
+void MemoryAllocator::PartialFreeMemory(MemoryChunk* chunk,
+                                        Address start_free) {
+  // We do not allow partial shrink for code.
+  DCHECK(chunk->executable() == NOT_EXECUTABLE);
+
+  intptr_t size;
+  base::VirtualMemory* reservation = chunk->reserved_memory();
+  DCHECK(reservation->IsReserved());
+  size = static_cast<intptr_t>(reservation->size());
+
+  size_t to_free_size = size - (start_free - chunk->address());
+
+  DCHECK(size_.Value() >= static_cast<intptr_t>(to_free_size));
+  size_.Increment(-static_cast<intptr_t>(to_free_size));
+  isolate_->counters()->memory_allocated()->Decrement(
+      static_cast<int>(to_free_size));
+  chunk->set_size(size - to_free_size);
+
+  reservation->ReleasePartial(start_free);
+}
+
 void MemoryAllocator::PreFreeMemory(MemoryChunk* chunk) {
   DCHECK(!chunk->IsFlagSet(MemoryChunk::PRE_FREED));
   LOG(isolate_, DeleteEvent("MemoryChunk", chunk));
@@ -2884,6 +2910,18 @@ void PagedSpace::ResetCodeAndMetadataStatistics(Isolate* isolate) {
 void MapSpace::VerifyObject(HeapObject* object) { CHECK(object->IsMap()); }
 #endif
 
+Address LargePage::GetAddressToShrink() {
+  HeapObject* object = GetObject();
+  if (executable() == EXECUTABLE) {
+    return 0;
+  }
+  size_t used_size = RoundUp((object->address() - address()) + object->Size(),
+                             base::OS::CommitPageSize());
+  if (used_size < CommittedPhysicalMemory()) {
+    return address() + used_size;
+  }
+  return 0;
+}
 
 // -----------------------------------------------------------------------------
 // LargeObjectIterator
@@ -3034,7 +3072,6 @@ void LargeObjectSpace::ClearMarkingStateOfLiveObjects() {
   }
 }
 
-
 void LargeObjectSpace::FreeUnmarkedObjects() {
   LargePage* previous = NULL;
   LargePage* current = first_page_;
@@ -3043,6 +3080,11 @@ void LargeObjectSpace::FreeUnmarkedObjects() {
     MarkBit mark_bit = Marking::MarkBitFrom(object);
     DCHECK(!Marking::IsGrey(mark_bit));
     if (Marking::IsBlack(mark_bit)) {
+      Address free_start;
+      if ((free_start = current->GetAddressToShrink()) != 0) {
+        // TODO(hpayer): Perform partial free concurrently.
+        heap()->memory_allocator()->PartialFreeMemory(current, free_start);
+      }
       previous = current;
       current = current->next_page();
     } else {