Record the addresses of pages that are unmapped to aid

src/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
@@ skipping 86 matching lines @@
       old_pointer_space_(NULL),
       old_data_space_(NULL),
       code_space_(NULL),
       map_space_(NULL),
       cell_space_(NULL),
       lo_space_(NULL),
       gc_state_(NOT_IN_GC),
       gc_post_processing_depth_(0),
       ms_count_(0),
       gc_count_(0),
+      remembered_unmapped_pages_index_(0),
       unflattened_strings_length_(0),
 #ifdef DEBUG
       allocation_allowed_(true),
       allocation_timeout_(0),
       disallow_allocation_failure_(false),
       debug_utils_(NULL),
 #endif  // DEBUG
       new_space_high_promotion_mode_active_(false),
       old_gen_promotion_limit_(kMinimumPromotionLimit),
       old_gen_allocation_limit_(kMinimumAllocationLimit),
@@ skipping 6847 matching lines @@
   }
   isolate_->heap()->store_buffer()->Compact();
   isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     isolate_->memory_allocator()->Free(chunk);
   }
   chunks_queued_for_free_ = NULL;
 }
 
+
+void Heap::RememberUnmappedPage(Address page, bool compacted) {
+  uintptr_t p = reinterpret_cast<uintptr_t>(page);
+  // Tag the page pointer to make it findable in the dump file.
+  if (compacted) {
+    p ^= 0xc1ead & (Page::kPageSize - 1);  // Cleared.
+  } else {
+    p ^= 0x1d1ed & (Page::kPageSize - 1);  // I died.
+  }
+  remembered_unmapped_pages_[remembered_unmapped_pages_index_] =
+      reinterpret_cast<Address>(p);
+  remembered_unmapped_pages_index_++;
+  remembered_unmapped_pages_index_ %= kRememberedUnmappedPages;
+}
+
 } }  // namespace v8::internal