Tweak compaction candidate selection to avoid keeping page with low occupancy around.

src/spaces.h

 // Copyright 2011 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
@@ skipping 1571 matching lines @@
 
   bool AdvanceSweeper(intptr_t bytes_to_sweep);
 
   bool IsSweepingComplete() {
     return !first_unswept_page_->is_valid();
   }
 
   Page* FirstPage() { return anchor_.next_page(); }
   Page* LastPage() { return anchor_.prev_page(); }
 
-  // Returns zero for pages that have so little fragmentation that it is not
-  // worth defragmenting them.  Otherwise a positive integer that gives an
-  // estimate of fragmentation on an arbitrary scale.
-  int Fragmentation(Page* p) {
-    FreeList::SizeStats sizes;
-    free_list_.CountFreeListItems(p, &sizes);
-
-    intptr_t ratio;
-    intptr_t ratio_threshold;
-    if (identity() == CODE_SPACE) {
-      ratio = (sizes.medium_size_ * 10 + sizes.large_size_ * 2) * 100 /
-          Page::kObjectAreaSize;
-      ratio_threshold = 10;
-    } else {
-      ratio = (sizes.small_size_ * 5 + sizes.medium_size_) * 100 /
-          Page::kObjectAreaSize;
-      ratio_threshold = 15;
-    }
-
-    if (FLAG_trace_fragmentation) {
-      PrintF("%p [%d]: %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %s\n",
-             reinterpret_cast<void*>(p),
-             identity(),
-             static_cast<int>(sizes.small_size_),
-             static_cast<double>(sizes.small_size_ * 100) /
-                 Page::kObjectAreaSize,
-             static_cast<int>(sizes.medium_size_),
-             static_cast<double>(sizes.medium_size_ * 100) /
-                 Page::kObjectAreaSize,
-             static_cast<int>(sizes.large_size_),
-             static_cast<double>(sizes.large_size_ * 100) /
-                 Page::kObjectAreaSize,
-             static_cast<int>(sizes.huge_size_),
-             static_cast<double>(sizes.huge_size_ * 100) /
-                 Page::kObjectAreaSize,
-             (ratio > ratio_threshold) ? "[fragmented]" : "");
-    }
-
-    if (FLAG_always_compact && sizes.Total() != Page::kObjectAreaSize) {
-      return 1;
-    }
-    if (ratio <= ratio_threshold) return 0;  // Not fragmented.
-
-    return static_cast<int>(ratio - ratio_threshold);
+  void CountFreeListItems(Page* p, FreeList::SizeStats* sizes) {
+    free_list_.CountFreeListItems(p, sizes);
   }
 
   void EvictEvacuationCandidatesFromFreeLists();
 
   bool CanExpand();
 
   // Returns the number of total pages in this space.
   int CountTotalPages();
 
  protected:
@@ skipping 1010 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_