Reland of "🏄 [heap] Add page evacuation mode for new->old"

src/heap/spaces-inl.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_SPACES_INL_H_
 #define V8_HEAP_SPACES_INL_H_
 
 #include "src/heap/incremental-marking.h"
 #include "src/heap/spaces.h"
 #include "src/isolate.h"
@@ skipping 269 matching lines @@
   DCHECK(!chunk->IsFlagSet(in_to_space ? MemoryChunk::IN_FROM_SPACE
                                        : MemoryChunk::IN_TO_SPACE));
   NewSpacePage* page = static_cast<NewSpacePage*>(chunk);
   heap->incremental_marking()->SetNewSpacePageFlags(page);
   return page;
 }
 
 // --------------------------------------------------------------------------
 // PagedSpace
 
+template <Page::InitializationMode mode>
 Page* Page::Initialize(Heap* heap, MemoryChunk* chunk, Executability executable,
                        PagedSpace* owner) {
   Page* page = reinterpret_cast<Page*>(chunk);
   page->mutex_ = new base::Mutex();
   DCHECK(page->area_size() <= kAllocatableMemory);
   DCHECK(chunk->owner() == owner);
 
   owner->IncreaseCapacity(page->area_size());
   heap->incremental_marking()->SetOldSpacePageFlags(chunk);
 
   // Make sure that categories are initialized before freeing the area.
   page->InitializeFreeListCategories();
-  owner->Free(page->area_start(), page->area_size());
+  // In the case we do not free the memory, we effectively account for the whole
+  // page as allocated memory that cannot be used for further allocations.
+  if (mode == kFreeMemory) {
+    owner->Free(page->area_start(), page->area_size());
+  }
 
   return page;
 }
 
+Page* Page::Convert(NewSpacePage* old_page, PagedSpace* new_owner) {
+  old_page->set_owner(new_owner);
+  old_page->SetFlags(0, ~0);
+  new_owner->AccountCommitted(old_page->size());
+  Page* new_page = Page::Initialize<kDoNotFreeMemory>(
+      old_page->heap(), old_page, NOT_EXECUTABLE, new_owner);
+  new_page->InsertAfter(new_owner->anchor()->prev_page());
+  return new_page;
+}
+
 void Page::InitializeFreeListCategories() {
   for (int i = kFirstCategory; i < kNumberOfCategories; i++) {
     categories_[i].Initialize(static_cast<FreeListCategoryType>(i));
   }
 }
 
 void MemoryChunk::IncrementLiveBytesFromGC(HeapObject* object, int by) {
   MemoryChunk::FromAddress(object->address())->IncrementLiveBytes(by);
 }
 
@@ skipping 412 matching lines @@
     other->allocation_info_.Reset(nullptr, nullptr);
     return true;
   }
   return false;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_INL_H_