A simple test for map compact.

Review URL: http://codereview.chromium.org/543113

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3655 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -201,6 +201,11 @@ DEFINE_bool(canonicalize_object_literal_maps, true,
 DEFINE_bool(use_big_map_space, true,
             "Use big map space, but don't compact if it grew too big.")
 
+DEFINE_int(max_map_space_pages, MapSpace::kMaxMapPageIndex - 1,
+           "Maximum number of pages in map space which still allows to encode "
+           "forwarding pointers.  That's actually a constant, but it's useful "
+           "to control it with a flag for better testing.")
+
 // mksnapshot.cc
 DEFINE_bool(h, false, "print this message")
 DEFINE_bool(new_snapshot, true, "use new snapshot implementation")

src/heap.cc

@@ -3544,7 +3544,8 @@ bool Heap::Setup(bool create_heap_objects) {
   // Initialize map space.
   map_space_ = new MapSpace(FLAG_use_big_map_space
       ? max_old_generation_size_
-      : (MapSpace::kMaxMapPageIndex + 1) * Page::kPageSize,
+      : MapSpace::kMaxMapPageIndex * Page::kPageSize,
+      FLAG_max_map_space_pages,
       MAP_SPACE);
   if (map_space_ == NULL) return false;
   if (!map_space_->Setup(NULL, 0)) return false;

src/spaces.h

@@ -1753,8 +1753,11 @@ class FixedSpace : public PagedSpace {
 class MapSpace : public FixedSpace {
  public:
   // Creates a map space object with a maximum capacity.
-  MapSpace(int max_capacity, AllocationSpace id)
-      : FixedSpace(max_capacity, id, Map::kSize, "map") {}
+  MapSpace(int max_capacity, int max_map_space_pages, AllocationSpace id)
+      : FixedSpace(max_capacity, id, Map::kSize, "map"),
+        max_map_space_pages_(max_map_space_pages) {
+    ASSERT(max_map_space_pages < kMaxMapPageIndex);
+  }
 
   // Prepares for a mark-compact GC.
   virtual void PrepareForMarkCompact(bool will_compact);
@@ -1762,8 +1765,7 @@ class MapSpace : public FixedSpace {
   // Given an index, returns the page address.
   Address PageAddress(int page_index) { return page_addresses_[page_index]; }
 
-  // Constants.
-  static const int kMaxMapPageIndex = (1 << MapWord::kMapPageIndexBits) - 1;
+  static const int kMaxMapPageIndex = 1 << MapWord::kMapPageIndexBits;
 
   // Are map pointers encodable into map word?
   bool MapPointersEncodable() {
@@ -1773,13 +1775,13 @@ class MapSpace : public FixedSpace {
     }
     int n_of_pages = Capacity() / Page::kObjectAreaSize;
     ASSERT(n_of_pages == CountTotalPages());
-    return n_of_pages <= kMaxMapPageIndex;
+    return n_of_pages <= max_map_space_pages_;
   }
 
   // Should be called after forced sweep to find out if map space needs
   // compaction.
   bool NeedsCompaction(int live_maps) {
-    return !MapPointersEncodable() && live_maps <= kCompactionThreshold;
+    return !MapPointersEncodable() && live_maps <= CompactionThreshold();
   }
 
   Address TopAfterCompaction(int live_maps) {
@@ -1838,10 +1840,14 @@ class MapSpace : public FixedSpace {
   static const int kMapsPerPage = Page::kObjectAreaSize / Map::kSize;
 
   // Do map space compaction if there is a page gap.
-  static const int kCompactionThreshold = kMapsPerPage * (kMaxMapPageIndex - 1);
+  int CompactionThreshold() {
+    return kMapsPerPage * (max_map_space_pages_ - 1);
+  }
+
+  const int max_map_space_pages_;
 
   // An array of page start address in a map space.
-  Address page_addresses_[kMaxMapPageIndex + 1];
+  Address page_addresses_[kMaxMapPageIndex];
 
  public:
   TRACK_MEMORY("MapSpace")

test/cctest/test-mark-compact.cc

@@ -207,6 +207,36 @@ TEST(MarkCompactCollector) {
 }
 
 
+static Handle<Map> CreateMap() {
+  return Factory::NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
+}
+
+
+TEST(MapCompact) {
+  FLAG_max_map_space_pages = 16;
+  InitializeVM();
+
+  {
+    v8::HandleScope sc;
+    // keep allocating maps while pointers are still encodable and thus
+    // mark compact is permitted.
+    Handle<JSObject> root = Factory::NewJSObjectFromMap(CreateMap());
+    do {
+      Handle<Map> map = CreateMap();
+      map->set_prototype(*root);
+      root = Factory::NewJSObjectFromMap(map);
+    } while (Heap::map_space()->MapPointersEncodable());
+  }
+  // Now, as we don't have any handles to just allocated maps, we should
+  // be able to trigger map compaction.
+  // To give an additional chance to fail, try to force compaction which
+  // should be impossible right now.
+  Heap::CollectAllGarbage(true);
+  // And now map pointers should be encodable again.
+  CHECK(Heap::map_space()->MapPointersEncodable());
+}
+
+
 static int gc_starts = 0;
 static int gc_ends = 0;