Adapt fragmentation heuristics for over reserved pages.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "execution.h"
 #include "factory.h"
 #include "macro-assembler.h"
 #include "global-handles.h"
@@ skipping 1881 matching lines @@
 
   Handle<JSObject> root =
       v8::Utils::OpenHandle(
           *v8::Handle<v8::Object>::Cast(
               v8::Context::GetCurrent()->Global()->Get(v8_str("root"))));
 
   // The root object should be in a sane state.
   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());
+}