Shrinking of PagedSpace is done only by sweeper.

src/spaces.cc

 // 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 1063 matching lines @@
     heap()->isolate()->memory_allocator()->Free(page);
   } else {
     heap()->QueueMemoryChunkForFree(page);
   }
 
   ASSERT(Capacity() > 0);
   accounting_stats_.ShrinkSpace(AreaSize());
 }
 
 
-void PagedSpace::ReleaseAllUnusedPages() {
-  PageIterator it(this);
-  while (it.has_next()) {
-    Page* page = it.next();
-    if (!page->WasSwept()) {
-      if (page->LiveBytes() == 0) ReleasePage(page);
-    } else {
-      HeapObject* obj = HeapObject::FromAddress(page->area_start());
-      if (obj->IsFreeSpace() &&
-          FreeSpace::cast(obj)->size() == AreaSize()) {
-        // Sometimes we allocate memory from free list but don't
-        // immediately initialize it (e.g. see PagedSpace::ReserveSpace
-        // called from Heap::ReserveSpace that can cause GC before
-        // reserved space is actually initialized).
-        // Thus we can't simply assume that obj represents a valid
-        // node still owned by a free list
-        // Instead we should verify that the page is fully covered
-        // by free list items.
-        FreeList::SizeStats sizes;
-        free_list_.CountFreeListItems(page, &sizes);
-        if (sizes.Total() == AreaSize()) {
-          ReleasePage(page);
-        }
-      }
-    }
-  }
-  heap()->FreeQueuedChunks();
-}
-
-
 #ifdef DEBUG
 void PagedSpace::Print() { }
 #endif
 
 #ifdef VERIFY_HEAP
 void PagedSpace::Verify(ObjectVisitor* visitor) {
   // We can only iterate over the pages if they were swept precisely.
   if (was_swept_conservatively_) return;
 
   bool allocation_pointer_found_in_space =
@@ skipping 2028 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal