[heap] Prepare code for smaller large object allocation limit than max allocatable memory.

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 "src/allocation.h"
 #include "src/atomic-utils.h"
 #include "src/base/atomicops.h"
@@ skipping 796 matching lines @@
   Address OffsetToAddress(int offset) {
     DCHECK_PAGE_OFFSET(offset);
     return address() + offset;
   }
 
   // ---------------------------------------------------------------------
 
   // Page size in bytes.  This must be a multiple of the OS page size.
   static const int kPageSize = 1 << kPageSizeBits;
 
-  // Maximum object size that fits in a page. Objects larger than that size
-  // are allocated in large object space and are never moved in memory. This
-  // also applies to new space allocation, since objects are never migrated
-  // from new space to large object space.  Takes double alignment into account.
+  // Maximum object size that gets allocated into regular pages. Objects larger
+  // than that size are allocated in large object space and are never moved in
+  // memory. This also applies to new space allocation, since objects are never
+  // migrated from new space to large object space. Takes double alignment into
+  // account.
   static const int kMaxRegularHeapObjectSize = kPageSize - kObjectStartOffset;
 
+  static const int kAllocatableMemory = kPageSize - kObjectStartOffset;
+
   // Page size mask.
   static const intptr_t kPageAlignmentMask = (1 << kPageSizeBits) - 1;
 
   inline void ClearGCFields();
 
   static inline Page* Initialize(Heap* heap, MemoryChunk* chunk,
                                  Executability executable, PagedSpace* owner);
 
   void InitializeAsAnchor(PagedSpace* owner);
 
@@ skipping 329 matching lines @@
 
   // Returns the maximum available executable bytes of heaps.
   intptr_t AvailableExecutable() {
     intptr_t executable_size = SizeExecutable();
     if (capacity_executable_ < executable_size) return 0;
     return capacity_executable_ - executable_size;
   }
 
   // Returns maximum available bytes that the old space can have.
   intptr_t MaxAvailable() {
-    return (Available() / Page::kPageSize) * Page::kMaxRegularHeapObjectSize;
+    return (Available() / Page::kPageSize) * Page::kAllocatableMemory;
   }
 
   // Returns an indication of whether a pointer is in a space that has
   // been allocated by this MemoryAllocator.
   V8_INLINE bool IsOutsideAllocatedSpace(const void* address) {
     return address < lowest_ever_allocated_.Value() ||
            address >= highest_ever_allocated_.Value();
   }
 
 #ifdef DEBUG
@@ skipping 55 matching lines @@
 
   static int CodePageAreaEndOffset();
 
   static int CodePageAreaSize() {
     return CodePageAreaEndOffset() - CodePageAreaStartOffset();
   }
 
   static int PageAreaSize(AllocationSpace space) {
     DCHECK_NE(LO_SPACE, space);
     return (space == CODE_SPACE) ? CodePageAreaSize()
-                                 : Page::kMaxRegularHeapObjectSize;
+                                 : Page::kAllocatableMemory;
   }
 
   MUST_USE_RESULT bool CommitExecutableMemory(base::VirtualMemory* vm,
                                               Address start, size_t commit_size,
                                               size_t reserved_size);
 
  private:
   Isolate* isolate_;
 
   // Maximum space size in bytes.
@@ skipping 434 matching lines @@
   FreeListCategory* large_list() { return &large_list_; }
   FreeListCategory* huge_list() { return &huge_list_; }
 
   PagedSpace* owner() { return owner_; }
   intptr_t wasted_bytes() { return wasted_bytes_; }
   base::Mutex* mutex() { return &mutex_; }
 
  private:
   // The size range of blocks, in bytes.
   static const int kMinBlockSize = 3 * kPointerSize;
-  static const int kMaxBlockSize = Page::kMaxRegularHeapObjectSize;
+  static const int kMaxBlockSize = Page::kAllocatableMemory;
 
   static const int kSmallListMin = 0x1f * kPointerSize;
   static const int kSmallListMax = 0xff * kPointerSize;
   static const int kMediumListMax = 0x7ff * kPointerSize;
   static const int kLargeListMax = 0x3fff * kPointerSize;
   static const int kSmallAllocationMax = kSmallListMin;
   static const int kMediumAllocationMax = kSmallListMax;
   static const int kLargeAllocationMax = kMediumListMax;
 
   FreeSpace* FindNodeFor(int size_in_bytes, int* node_size);
@@ skipping 399 matching lines @@
 
 class NewSpacePage : public MemoryChunk {
  public:
   // GC related flags copied from from-space to to-space when
   // flipping semispaces.
   static const intptr_t kCopyOnFlipFlagsMask =
       (1 << MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING) |
       (1 << MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING) |
       (1 << MemoryChunk::SCAN_ON_SCAVENGE);
 
-  static const int kAreaSize = Page::kMaxRegularHeapObjectSize;
+  static const int kAreaSize = Page::kAllocatableMemory;
 
   inline NewSpacePage* next_page() {
     return static_cast<NewSpacePage*>(next_chunk());
   }
 
   inline void set_next_page(NewSpacePage* page) { set_next_chunk(page); }
 
   inline NewSpacePage* prev_page() {
     return static_cast<NewSpacePage*>(prev_chunk());
   }
@@ skipping 698 matching lines @@
       return RoundDown(size, Map::kSize);
     } else {
       return (size / Map::kSize) * Map::kSize;
     }
   }
 
  protected:
   virtual void VerifyObject(HeapObject* obj);
 
  private:
-  static const int kMapsPerPage = Page::kMaxRegularHeapObjectSize / Map::kSize;
+  static const int kMapsPerPage = Page::kAllocatableMemory / Map::kSize;
 
   // Do map space compaction if there is a page gap.
   int CompactionThreshold() {
     return kMapsPerPage * (max_map_space_pages_ - 1);
   }
 
   const int max_map_space_pages_;
 };
 
 
@@ skipping 134 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_