1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_GC_SHARED_CARDTABLE_HPP
  26 #define SHARE_GC_SHARED_CARDTABLE_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "memory/memRegion.hpp"
  30 #include "oops/oopsHierarchy.hpp"
  31 #include "utilities/align.hpp"
  32 
  33 class CardTable: public CHeapObj<mtGC> {
  34   friend class VMStructs;
  35 public:
  36   typedef uint8_t CardValue;
  37 
  38   // All code generators assume that the size of a card table entry is one byte.
  39   // They need to be updated to reflect any change to this.
  40   // This code can typically be found by searching for the byte_map_base() method.
  41   STATIC_ASSERT(sizeof(CardValue) == 1);
  42 
  43 protected:
  44   // The declaration order of these const fields is important; see the
  45   // constructor before changing.
  46   const bool      _scanned_concurrently;
  47   const MemRegion _whole_heap;       // the region covered by the card table
  48   size_t          _guard_index;      // index of very last element in the card
  49                                      // table; it is set to a guard value
  50                                      // (last_card) and should never be modified
  51   size_t          _last_valid_index; // index of the last valid element
  52   const size_t    _page_size;        // page size used when mapping _byte_map
  53   size_t          _byte_map_size;    // in bytes
  54   CardValue*      _byte_map;         // the card marking array
  55   CardValue*      _byte_map_base;
  56 
  57   int _cur_covered_regions;
  58 
  59   // The covered regions should be in address order.
  60   MemRegion* _covered;
  61   // The committed regions correspond one-to-one to the covered regions.
  62   // They represent the card-table memory that has been committed to service
  63   // the corresponding covered region.  It may be that committed region for
  64   // one covered region corresponds to a larger region because of page-size
  65   // roundings.  Thus, a committed region for one covered region may
  66   // actually extend onto the card-table space for the next covered region.
  67   MemRegion* _committed;
  68 
  69   // The last card is a guard card, and we commit the page for it so
  70   // we can use the card for verification purposes. We make sure we never
  71   // uncommit the MemRegion for that page.
  72   MemRegion _guard_region;
  73 
  74   inline size_t compute_byte_map_size();
  75 
  76   // Finds and return the index of the region, if any, to which the given
  77   // region would be contiguous.  If none exists, assign a new region and
  78   // returns its index.  Requires that no more than the maximum number of
  79   // covered regions defined in the constructor are ever in use.
  80   int find_covering_region_by_base(HeapWord* base);
  81 
  82   // Same as above, but finds the region containing the given address
  83   // instead of starting at a given base address.
  84   int find_covering_region_containing(HeapWord* addr);
  85 
  86   // Returns the leftmost end of a committed region corresponding to a
  87   // covered region before covered region "ind", or else "NULL" if "ind" is
  88   // the first covered region.
  89   HeapWord* largest_prev_committed_end(int ind) const;
  90 
  91   // Returns the part of the region mr that doesn't intersect with
  92   // any committed region other than self.  Used to prevent uncommitting
  93   // regions that are also committed by other regions.  Also protects
  94   // against uncommitting the guard region.
  95   MemRegion committed_unique_to_self(int self, MemRegion mr) const;
  96 
  97   // Some barrier sets create tables whose elements correspond to parts of
  98   // the heap; the CardTableBarrierSet is an example.  Such barrier sets will
  99   // normally reserve space for such tables, and commit parts of the table
 100   // "covering" parts of the heap that are committed. At most one covered
 101   // region per generation is needed.
 102   static const int _max_covered_regions = 2;
 103 
 104   enum CardValues {
 105     clean_card                  = (CardValue)-1,
 106 
 107     dirty_card                  =  0,
 108     precleaned_card             =  1,
 109     last_card                   =  2,
 110     CT_MR_BS_last_reserved      =  4
 111   };
 112 
 113   // a word's worth (row) of clean card values
 114   static const intptr_t clean_card_row = (intptr_t)(-1);
 115 
 116 public:
 117   CardTable(MemRegion whole_heap, bool conc_scan);
 118   virtual ~CardTable();
 119   virtual void initialize();
 120 
 121   // The kinds of precision a CardTable may offer.
 122   enum PrecisionStyle {
 123     Precise,
 124     ObjHeadPreciseArray
 125   };
 126 
 127   // Tells what style of precision this card table offers.
 128   PrecisionStyle precision() {
 129     return ObjHeadPreciseArray; // Only one supported for now.
 130   }
 131 
 132   // *** Barrier set functions.
 133 
 134   // Initialization utilities; covered_words is the size of the covered region
 135   // in, um, words.
 136   inline size_t cards_required(size_t covered_words) {
 137     // Add one for a guard card, used to detect errors.
 138     const size_t words = align_up(covered_words, card_size_in_words);
 139     return words / card_size_in_words + 1;
 140   }
 141 
 142   // Dirty the bytes corresponding to "mr" (not all of which must be
 143   // covered.)
 144   void dirty_MemRegion(MemRegion mr);
 145 
 146   // Clear (to clean_card) the bytes entirely contained within "mr" (not
 147   // all of which must be covered.)
 148   void clear_MemRegion(MemRegion mr);
 149 
 150   // Return true if "p" is at the start of a card.
 151   bool is_card_aligned(HeapWord* p) {
 152     CardValue* pcard = byte_for(p);
 153     return (addr_for(pcard) == p);
 154   }
 155 
 156   // Mapping from address to card marking array entry
 157   CardValue* byte_for(const void* p) const {
 158     assert(_whole_heap.contains(p),
 159            "Attempt to access p = " PTR_FORMAT " out of bounds of "
 160            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
 161            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
 162     CardValue* result = &_byte_map_base[uintptr_t(p) >> card_shift];
 163     assert(result >= _byte_map && result < _byte_map + _byte_map_size,
 164            "out of bounds accessor for card marking array");
 165     return result;
 166   }
 167 
 168   // The card table byte one after the card marking array
 169   // entry for argument address. Typically used for higher bounds
 170   // for loops iterating through the card table.
 171   CardValue* byte_after(const void* p) const {
 172     return byte_for(p) + 1;
 173   }
 174 
 175   virtual void invalidate(MemRegion mr);
 176   void clear(MemRegion mr);
 177   void dirty(MemRegion mr);
 178 
 179   // Provide read-only access to the card table array.
 180   const CardValue* byte_for_const(const void* p) const {
 181     return byte_for(p);
 182   }
 183   const CardValue* byte_after_const(const void* p) const {
 184     return byte_after(p);
 185   }
 186 
 187   // Mapping from card marking array entry to address of first word
 188   HeapWord* addr_for(const CardValue* p) const {
 189     assert(p >= _byte_map && p < _byte_map + _byte_map_size,
 190            "out of bounds access to card marking array. p: " PTR_FORMAT
 191            " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
 192            p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
 193     size_t delta = pointer_delta(p, _byte_map_base, sizeof(CardValue));
 194     HeapWord* result = (HeapWord*) (delta << card_shift);
 195     assert(_whole_heap.contains(result),
 196            "Returning result = " PTR_FORMAT " out of bounds of "
 197            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
 198            p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
 199     return result;
 200   }
 201 
 202   // Mapping from address to card marking array index.
 203   size_t index_for(void* p) {
 204     assert(_whole_heap.contains(p),
 205            "Attempt to access p = " PTR_FORMAT " out of bounds of "
 206            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
 207            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
 208     return byte_for(p) - _byte_map;
 209   }
 210 
 211   CardValue* byte_for_index(const size_t card_index) const {
 212     return _byte_map + card_index;
 213   }
 214 
 215   // Resize one of the regions covered by the remembered set.
 216   virtual void resize_covered_region(MemRegion new_region);
 217 
 218   // *** Card-table-RemSet-specific things.
 219 
 220   static uintx ct_max_alignment_constraint();
 221 
 222   // Apply closure "cl" to the dirty cards containing some part of
 223   // MemRegion "mr".
 224   void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
 225 
 226   // Return the MemRegion corresponding to the first maximal run
 227   // of dirty cards lying completely within MemRegion mr.
 228   // If reset is "true", then sets those card table entries to the given
 229   // value.
 230   MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
 231                                          int reset_val);
 232 
 233   // Constants
 234   enum SomePublicConstants {
 235     card_shift                  = 9,
 236     card_size                   = 1 << card_shift,
 237     card_size_in_words          = card_size / sizeof(HeapWord)
 238   };
 239 
 240   static CardValue clean_card_val()          { return clean_card; }
 241   static CardValue dirty_card_val()          { return dirty_card; }
 242   static CardValue precleaned_card_val()     { return precleaned_card; }
 243   static intptr_t clean_card_row_val()   { return clean_card_row; }
 244 
 245   // Card marking array base (adjusted for heap low boundary)
 246   // This would be the 0th element of _byte_map, if the heap started at 0x0.
 247   // But since the heap starts at some higher address, this points to somewhere
 248   // before the beginning of the actual _byte_map.
 249   CardValue* byte_map_base() const { return _byte_map_base; }
 250   bool scanned_concurrently() const { return _scanned_concurrently; }
 251 
 252   virtual bool is_in_young(oop obj) const = 0;
 253 
 254   // Print a description of the memory for the card table
 255   virtual void print_on(outputStream* st) const;
 256 
 257   void verify();
 258   void verify_guard();
 259 
 260   // val_equals -> it will check that all cards covered by mr equal val
 261   // !val_equals -> it will check that all cards covered by mr do not equal val
 262   void verify_region(MemRegion mr, CardValue val, bool val_equals) PRODUCT_RETURN;
 263   void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
 264   void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
 265 };
 266 
 267 #endif // SHARE_GC_SHARED_CARDTABLE_HPP