X64: Reenabled RSet.

src/spaces.h

 // Copyright 2006-2008 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 81 matching lines @@
 // three areas: the first two words are used for bookkeeping, the next 248
 // bytes are used as remembered set, and the rest of the page is the object
 // area.
 //
 // Pointers are aligned to the pointer size (4), only 1 bit is needed
 // for a pointer in the remembered set. Given an address, its remembered set
 // bit position (offset from the start of the page) is calculated by dividing
 // its page offset by 32. Therefore, the object area in a page starts at the
 // 256th byte (8K/32). Bytes 0 to 255 do not need the remembered set, so that
 // the first two words (64 bits) in a page can be used for other purposes.
-// TODO(X64): This description only represents the 32-bit layout.
-// On the 64-bit platform, we add an offset to the start of the remembered set.
+//
+// On the 64-bit platform, we add an offset to the start of the remembered set,
+// and pointers are aligned to 8-byte pointer size. This means that we need
+// only 128 bytes for the RSet, and only get two bytes free in the RSet's RSet.
+// For this reason we add an offset to get room for the Page data at the start.
 //
 // The mark-compact collector transforms a map pointer into a page index and a
 // page offset. The map space can have up to 1024 pages, and 8M bytes (1024 *
 // 8K) in total.  Because a map pointer is aligned to the pointer size (4
 // bytes), 11 bits are enough to encode the page offset. 21 bits (10 for the
 // page index + 11 for the offset in the page) are required to encode a map
 // pointer.
 //
 // The only way to get a page pointer is by calling factory methods:
 //   Page* p = Page::FromAddress(addr); or
 //   Page* p = Page::FromAllocationTop(top);
 class Page {
  public:
   // Returns the page containing a given address. The address ranges
   // from [page_addr .. page_addr + kPageSize[
   //
   // Note that this function only works for addresses in normal paged
-  // spaces and addresses in the first 8K of large object pages (ie,
+  // spaces and addresses in the first 8K of large object pages (i.e.,
   // the start of large objects but not necessarily derived pointers
   // within them).
   INLINE(static Page* FromAddress(Address a)) {
     return reinterpret_cast<Page*>(OffsetFrom(a) & ~kPageAlignmentMask);
   }
 
   // Returns the page containing an allocation top. Because an allocation
   // top address can be the upper bound of the page, we need to subtract
   // it with kPointerSize first. The address ranges from
   // [page_addr + kObjectStartOffset .. page_addr + kPageSize].
@@ skipping 79 matching lines @@
 
   // 8K bytes per page.
   static const int kPageSizeBits = 13;
 
   // Page size in bytes.  This must be a multiple of the OS page size.
   static const int kPageSize = 1 << kPageSizeBits;
 
   // Page size mask.
   static const intptr_t kPageAlignmentMask = (1 << kPageSizeBits) - 1;
 
-  // The offset of the remembered set in a page, in addition to the empty words
+  // The offset of the remembered set in a page, in addition to the empty bytes
   // formed as the remembered bits of the remembered set itself.
 #ifdef V8_TARGET_ARCH_X64
   static const int kRSetOffset = 4 * kPointerSize;  // Room for four pointers.
 #else
   static const int kRSetOffset = 0;
 #endif
   // The end offset of the remembered set in a page
   // (heaps are aligned to pointer size).
   static const int kRSetEndOffset = kRSetOffset + kPageSize / kBitsPerPointer;
 
   // The start offset of the object area in a page.
   // This needs to be at least (bits per uint32_t) * kBitsPerPointer,
   // to align start of rset to a uint32_t address.
   static const int kObjectStartOffset = 256;
 
-  // The start offset of the remembered set in a page.
+  // The start offset of the used part of the remembered set in a page.
   static const int kRSetStartOffset = kRSetOffset +
       kObjectStartOffset / kBitsPerPointer;
 
   // Object area size in bytes.
   static const int kObjectAreaSize = kPageSize - kObjectStartOffset;
 
   // Maximum object size that fits in a page.
   static const int kMaxHeapObjectSize = kObjectAreaSize;
 
   //---------------------------------------------------------------------------
   // Page header description.
   //
   // If a page is not in the large object space, the first word,
   // opaque_header, encodes the next page address (aligned to kPageSize 8K)
   // and the chunk number (0 ~ 8K-1).  Only MemoryAllocator should use
   // opaque_header. The value range of the opaque_header is [0..kPageSize[,
   // or [next_page_start, next_page_end[. It cannot point to a valid address
   // in the current page.  If a page is in the large object space, the first
   // word *may* (if the page start and large object chunk start are the
   // same) contain the address of the next large object chunk.
   intptr_t opaque_header;
 
   // If the page is not in the large object space, the low-order bit of the
   // second word is set. If the page is in the large object space, the
   // second word *may* (if the page start and large object chunk start are
   // the same) contain the large object chunk size.  In either case, the
   // low-order bit for large object pages will be cleared.
   int is_normal_page;
 
-  // The following fields overlap with remembered set, they can only
+  // The following fields may overlap with remembered set, they can only
   // be used in the mark-compact collector when remembered set is not
   // used.
 
+  // The index of the page in its owner space.
+  int mc_page_index;
+
   // The allocation pointer after relocating objects to this page.
   Address mc_relocation_top;
 
-  // The index of the page in its owner space.
-  int mc_page_index;
-
   // The forwarding address of the first live object in this page.
   Address mc_first_forwarded;
 
 #ifdef DEBUG
  private:
   static RSetState rset_state_;  // state of the remembered set
 #endif
 };
 
 
@@ skipping 871 matching lines @@
   Address bottom() { return to_space_.low(); }
 
   // Get the age mark of the inactive semispace.
   Address age_mark() { return from_space_.age_mark(); }
   // Set the age mark in the active semispace.
   void set_age_mark(Address mark) { to_space_.set_age_mark(mark); }
 
   // The start address of the space and a bit mask. Anding an address in the
   // new space with the mask will result in the start address.
   Address start() { return start_; }
-  uint32_t mask() { return address_mask_; }
+  uintptr_t mask() { return address_mask_; }
 
   // The allocation top and limit addresses.
   Address* allocation_top_address() { return &allocation_info_.top; }
   Address* allocation_limit_address() { return &allocation_info_.limit; }
 
   Object* AllocateRaw(int size_in_bytes) {
     return AllocateRawInternal(size_in_bytes, &allocation_info_);
   }
 
   // Allocate the requested number of bytes for relocation during mark-compact
@@ skipping 627 matching lines @@
 
  private:
   LargeObjectChunk* current_;
   HeapObjectCallback size_func_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_