[vm] Compute per-HeapPage usage during sweeping.

runtime/vm/pages.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/pages.h"
 
 #include "platform/address_sanitizer.h"
 #include "platform/assert.h"
 #include "vm/compiler_stats.h"
 #include "vm/gc_marker.h"
@@ skipping 53 matching lines @@
   bool is_executable = (type == kExecutable);
   // Create the new page executable (RWX) only if we're not in W^X mode
   bool create_executable = !FLAG_write_protect_code && is_executable;
   if (!memory->Commit(create_executable, name)) {
     return NULL;
   }
   HeapPage* result = reinterpret_cast<HeapPage*>(memory->address());
   ASSERT(result != NULL);
   result->memory_ = memory;
   result->next_ = NULL;
+  result->used_in_bytes_ = 0;
   result->type_ = type;
 
   LSAN_REGISTER_ROOT_REGION(result, sizeof(*result));
 
   return result;
 }
 
 HeapPage* HeapPage::Allocate(intptr_t size_in_words,
                              PageType type,
                              const char* name) {
@@ skipping 1001 matching lines @@
   uword offset = HeapPage::ObjectStartOffset();
   pointer = reinterpret_cast<void*>(reinterpret_cast<uword>(pointer) - offset);
   size += offset;
 
   VirtualMemory* memory = VirtualMemory::ForImagePage(pointer, size);
   ASSERT(memory != NULL);
   HeapPage* page = reinterpret_cast<HeapPage*>(malloc(sizeof(HeapPage)));
   page->memory_ = memory;
   page->next_ = NULL;
   page->object_end_ = memory->end();
+  page->used_in_bytes_ = page->object_end_ - page->object_start();
 
   MutexLocker ml(pages_lock_);
   HeapPage **first, **tail;
   if (is_executable) {
     ASSERT(Utils::IsAligned(pointer, OS::PreferredCodeAlignment()));
     page->type_ = HeapPage::kExecutable;
     first = &exec_pages_;
     tail = &exec_pages_tail_;
   } else {
     page->type_ = HeapPage::kData;
@@ skipping 169 matching lines @@
     return 0;
   } else {
     ASSERT(total_time >= gc_time);
     int result = static_cast<int>(
         (static_cast<double>(gc_time) / static_cast<double>(total_time)) * 100);
     return result;
   }
 }
 
 }  // namespace dart