[heap] Reland uncommit unused large object page memory.

test/cctest/heap/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
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                                    isolate_is_locked);
   int mark_sweep_count_after = heap->ms_count();
   int mark_sweeps_performed = mark_sweep_count_after - mark_sweep_count_before;
   // The memory pressuer handler either performed two GCs or performed one and
   // started incremental marking.
   CHECK(mark_sweeps_performed == 2 ||
         (mark_sweeps_performed == 1 &&
          !heap->incremental_marking()->IsStopped()));
 }
 
+TEST(UncommitUnusedLargeObjectMemory) {
+  CcTest::InitializeVM();
+  v8::HandleScope scope(CcTest::isolate());
+  Heap* heap = CcTest::heap();
+  Isolate* isolate = heap->isolate();
+
+  Handle<FixedArray> array = isolate->factory()->NewFixedArray(200000);
+  MemoryChunk* chunk = MemoryChunk::FromAddress(array->address());
+  CHECK(chunk->owner()->identity() == LO_SPACE);
+
+  intptr_t size_before = array->Size();
+  size_t committed_memory_before = chunk->CommittedPhysicalMemory();
+
+  array->Shrink(1);
+  CHECK(array->Size() < size_before);
+
+  CcTest::heap()->CollectAllGarbage();
+  CHECK(chunk->CommittedPhysicalMemory() < committed_memory_before);
+  size_t shrinked_size =
+      RoundUp((array->address() - chunk->address()) + array->Size(),
+              base::OS::CommitPageSize());
+  CHECK_EQ(shrinked_size, chunk->CommittedPhysicalMemory());
+}
 }  // namespace internal
 }  // namespace v8