[heap,snapshot] Replace first page size from snapshots with page trimming

src/heap/spaces.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_H_
 #define V8_HEAP_SPACES_H_
 
 #include <list>
 #include <memory>
 #include <unordered_set>
@@ skipping 799 matching lines @@
 
   bool is_anchor() { return IsFlagSet(Page::ANCHOR); }
 
   intptr_t wasted_memory() { return wasted_memory_.Value(); }
   void add_wasted_memory(intptr_t waste) { wasted_memory_.Increment(waste); }
   intptr_t available_in_free_list() { return available_in_free_list_.Value(); }
   void add_available_in_free_list(intptr_t available) {
     available_in_free_list_.Increment(available);
   }
 
+  size_t ShrinkToHighWaterMark();
+
 #ifdef DEBUG
   void Print();
 #endif  // DEBUG
 
  private:
   enum InitializationMode { kFreeMemory, kDoNotFreeMemory };
 
   template <InitializationMode mode = kFreeMemory>
   static inline Page* Initialize(Heap* heap, MemoryChunk* chunk,
                                  Executability executable, PagedSpace* owner);
@@ skipping 468 matching lines @@
   void ReportStatistics();
 #endif
 
   // Returns a MemoryChunk in which the memory region from commit_area_size to
   // reserve_area_size of the chunk area is reserved but not committed, it
   // could be committed later by calling MemoryChunk::CommitArea.
   MemoryChunk* AllocateChunk(intptr_t reserve_area_size,
                              intptr_t commit_area_size,
                              Executability executable, Space* space);
 
+  void ShrinkChunk(MemoryChunk* chunk, size_t bytes_to_shrink);
+
   Address ReserveAlignedMemory(size_t requested, size_t alignment,
                                base::VirtualMemory* controller);
   Address AllocateAlignedMemory(size_t reserve_size, size_t commit_size,
                                 size_t alignment, Executability executable,
                                 base::VirtualMemory* controller);
 
   bool CommitMemory(Address addr, size_t size, Executability executable);
 
   void FreeMemory(base::VirtualMemory* reservation, Executability executable);
   void PartialFreeMemory(MemoryChunk* chunk, Address start_free);
@@ skipping 861 matching lines @@
   FreeList* free_list() { return &free_list_; }
 
   base::Mutex* mutex() { return &space_mutex_; }
 
   inline void UnlinkFreeListCategories(Page* page);
   inline intptr_t RelinkFreeListCategories(Page* page);
 
   iterator begin() { return iterator(anchor_.next_page()); }
   iterator end() { return iterator(&anchor_); }
 
+  // Shrink immortal immovable pages of the space to be exactly the size needed
+  // using the high water mark.
+  void ShrinkImmortalImmovablePages();
+
  protected:
   // PagedSpaces that should be included in snapshots have different, i.e.,
   // smaller, initial pages.
   virtual bool snapshotable() { return true; }
 
   bool HasPages() { return anchor_.next_page() != &anchor_; }
 
   // Cleans up the space, frees all pages in this space except those belonging
   // to the initial chunk, uncommits addresses in the initial chunk.
   void TearDown();
@@ skipping 832 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_H_