Adapt fragmentation heuristics for over reserved pages.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index 179ca1c63cd1f2add33dfeeaf10fe8081cc89e80..e7ff3d0b26e28aac94b15266921e5d151ff1d860 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -1899,3 +1899,42 @@ TEST(Regress2143b) {
   CHECK(root->IsJSObject());
   CHECK(root->map()->IsMap());
 }
+
+
+// Implemented in the test-alloc.cc test suite.
+void SimulateFullSpace(PagedSpace* space);
+
+
+TEST(ReleaseOverReservedPages) {
+  i::FLAG_trace_gc = true;
+  InitializeVM();
+  v8::HandleScope scope;
+  static const int number_of_test_pages = 20;
+
+  // Prepare many pages with low live-bytes count.
+  PagedSpace* old_pointer_space = HEAP->old_pointer_space();
+  CHECK_EQ(1, old_pointer_space->CountTotalPages());
+  for (int i = 0; i < number_of_test_pages; i++) {
+    AlwaysAllocateScope always_allocate;
+    SimulateFullSpace(old_pointer_space);
+    FACTORY->NewFixedArray(1, TENURED);
+  }
+  CHECK_EQ(number_of_test_pages + 1, old_pointer_space->CountTotalPages());
+
+  // Triggering one GC will cause a lot of garbage to be discovered but
+  // even spread across all allocated pages.
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags, "triggered for preparation");
+  CHECK_EQ(number_of_test_pages + 1, old_pointer_space->CountTotalPages());
+
+  // Triggering subsequent GCs should cause at least half of the pages
+  // to be released to the OS after at most two cycles.
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags, "triggered by test 1");
+  CHECK_GE(number_of_test_pages + 1, old_pointer_space->CountTotalPages());
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags, "triggered by test 2");
+  CHECK_GE(number_of_test_pages + 1, old_pointer_space->CountTotalPages() * 2);
+
+  // Triggering a last-resort GC should cause all pages to be released
+  // to the OS so that other processes can seize the memory.
+  HEAP->CollectAllAvailableGarbage("triggered really hard");
+  CHECK_EQ(1, old_pointer_space->CountTotalPages());
+}