1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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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  24 
  25 #ifndef SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP
  26 #define SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP
  27 
  28 #include "gc/shared/modRefBarrierSet.hpp"
  29 #include "oops/oop.hpp"
  30 
  31 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
  32 // enumerate ref fields that have been modified (since the last
  33 // enumeration.)
  34 
  35 // As it currently stands, this barrier is *imprecise*: when a ref field in
  36 // an object "o" is modified, the card table entry for the card containing
  37 // the head of "o" is dirtied, not necessarily the card containing the
  38 // modified field itself.  For object arrays, however, the barrier *is*
  39 // precise; only the card containing the modified element is dirtied.
  40 // Closures used to scan dirty cards should take these
  41 // considerations into account.
  42 
  43 class CardTableModRefBS: public ModRefBarrierSet {
  44   // Some classes get to look at some private stuff.
  45   friend class VMStructs;
  46  protected:
  47 
  48   enum CardValues {
  49     clean_card                  = -1,
  50     // The mask contains zeros in places for all other values.
  51     clean_card_mask             = clean_card - 31,
  52 
  53     dirty_card                  =  0,
  54     precleaned_card             =  1,
  55     claimed_card                =  2,
  56     deferred_card               =  4,
  57     last_card                   =  8,
  58     CT_MR_BS_last_reserved      = 16
  59   };
  60 
  61   // a word's worth (row) of clean card values
  62   static const intptr_t clean_card_row = (intptr_t)(-1);
  63 
  64   // The declaration order of these const fields is important; see the
  65   // constructor before changing.
  66   const MemRegion _whole_heap;       // the region covered by the card table
  67   size_t          _guard_index;      // index of very last element in the card
  68                                      // table; it is set to a guard value
  69                                      // (last_card) and should never be modified
  70   size_t          _last_valid_index; // index of the last valid element
  71   const size_t    _page_size;        // page size used when mapping _byte_map
  72   size_t          _byte_map_size;    // in bytes
  73   jbyte*          _byte_map;         // the card marking array
  74 
  75   int _cur_covered_regions;
  76   // The covered regions should be in address order.
  77   MemRegion* _covered;
  78   // The committed regions correspond one-to-one to the covered regions.
  79   // They represent the card-table memory that has been committed to service
  80   // the corresponding covered region.  It may be that committed region for
  81   // one covered region corresponds to a larger region because of page-size
  82   // roundings.  Thus, a committed region for one covered region may
  83   // actually extend onto the card-table space for the next covered region.
  84   MemRegion* _committed;
  85 
  86   // The last card is a guard card, and we commit the page for it so
  87   // we can use the card for verification purposes. We make sure we never
  88   // uncommit the MemRegion for that page.
  89   MemRegion _guard_region;
  90 
  91  protected:
  92   inline size_t compute_byte_map_size();
  93 
  94   // Finds and return the index of the region, if any, to which the given
  95   // region would be contiguous.  If none exists, assign a new region and
  96   // returns its index.  Requires that no more than the maximum number of
  97   // covered regions defined in the constructor are ever in use.
  98   int find_covering_region_by_base(HeapWord* base);
  99 
 100   // Same as above, but finds the region containing the given address
 101   // instead of starting at a given base address.
 102   int find_covering_region_containing(HeapWord* addr);
 103 
 104   // Resize one of the regions covered by the remembered set.
 105   virtual void resize_covered_region(MemRegion new_region);
 106 
 107   // Returns the leftmost end of a committed region corresponding to a
 108   // covered region before covered region "ind", or else "NULL" if "ind" is
 109   // the first covered region.
 110   HeapWord* largest_prev_committed_end(int ind) const;
 111 
 112   // Returns the part of the region mr that doesn't intersect with
 113   // any committed region other than self.  Used to prevent uncommitting
 114   // regions that are also committed by other regions.  Also protects
 115   // against uncommitting the guard region.
 116   MemRegion committed_unique_to_self(int self, MemRegion mr) const;
 117 
 118   // Mapping from address to card marking array entry
 119   jbyte* byte_for(const void* p) const {
 120     assert(_whole_heap.contains(p),
 121            "Attempt to access p = " PTR_FORMAT " out of bounds of "
 122            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
 123            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
 124     jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
 125     assert(result >= _byte_map && result < _byte_map + _byte_map_size,
 126            "out of bounds accessor for card marking array");
 127     return result;
 128   }
 129 
 130   // The card table byte one after the card marking array
 131   // entry for argument address. Typically used for higher bounds
 132   // for loops iterating through the card table.
 133   jbyte* byte_after(const void* p) const {
 134     return byte_for(p) + 1;
 135   }
 136 
 137  protected:
 138   // Dirty the bytes corresponding to "mr" (not all of which must be
 139   // covered.)
 140   void dirty_MemRegion(MemRegion mr);
 141 
 142   // Clear (to clean_card) the bytes entirely contained within "mr" (not
 143   // all of which must be covered.)
 144   void clear_MemRegion(MemRegion mr);
 145 
 146 public:
 147   // Constants
 148   enum SomePublicConstants {
 149     card_shift                  = 9,
 150     card_size                   = 1 << card_shift,
 151     card_size_in_words          = card_size / sizeof(HeapWord)
 152   };
 153 
 154   static int clean_card_val()      { return clean_card; }
 155   static int clean_card_mask_val() { return clean_card_mask; }
 156   static int dirty_card_val()      { return dirty_card; }
 157   static int claimed_card_val()    { return claimed_card; }
 158   static int precleaned_card_val() { return precleaned_card; }
 159   static int deferred_card_val()   { return deferred_card; }
 160 
 161   virtual void initialize();
 162 
 163   // *** Barrier set functions.
 164 
 165   bool has_write_ref_pre_barrier() { return false; }
 166 
 167   // Initialization utilities; covered_words is the size of the covered region
 168   // in, um, words.
 169   inline size_t cards_required(size_t covered_words) {
 170     // Add one for a guard card, used to detect errors.
 171     const size_t words = align_up(covered_words, card_size_in_words);
 172     return words / card_size_in_words + 1;
 173   }
 174 
 175 protected:
 176 
 177   CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);
 178   ~CardTableModRefBS();
 179 
 180   // Record a reference update. Note that these versions are precise!
 181   // The scanning code has to handle the fact that the write barrier may be
 182   // either precise or imprecise. We make non-virtual inline variants of
 183   // these functions here for performance.
 184 
 185   void write_ref_field_work(oop obj, size_t offset, oop newVal);
 186   virtual void write_ref_field_work(void* field, oop newVal, bool release);
 187 public:
 188 
 189   bool has_write_ref_array_opt() { return true; }
 190   bool has_write_region_opt() { return true; }
 191 
 192   inline void inline_write_region(MemRegion mr) {
 193     dirty_MemRegion(mr);
 194   }
 195 protected:
 196   void write_region_work(MemRegion mr) {
 197     inline_write_region(mr);
 198   }
 199 public:
 200 
 201   inline void inline_write_ref_array(MemRegion mr) {
 202     dirty_MemRegion(mr);
 203   }
 204 protected:
 205   void write_ref_array_work(MemRegion mr) {
 206     inline_write_ref_array(mr);
 207   }
 208 public:
 209 
 210   bool is_aligned(HeapWord* addr) {
 211     return is_card_aligned(addr);
 212   }
 213 
 214   // *** Card-table-barrier-specific things.
 215 
 216   template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}
 217 
 218   template <class T> inline void inline_write_ref_field(T* field, oop newVal, bool release);
 219 
 220   // These are used by G1, when it uses the card table as a temporary data
 221   // structure for card claiming.
 222   bool is_card_dirty(size_t card_index) {
 223     return _byte_map[card_index] == dirty_card_val();
 224   }
 225 
 226   void mark_card_dirty(size_t card_index) {
 227     _byte_map[card_index] = dirty_card_val();
 228   }
 229 
 230   bool is_card_clean(size_t card_index) {
 231     return _byte_map[card_index] == clean_card_val();
 232   }
 233 
 234   // Card marking array base (adjusted for heap low boundary)
 235   // This would be the 0th element of _byte_map, if the heap started at 0x0.
 236   // But since the heap starts at some higher address, this points to somewhere
 237   // before the beginning of the actual _byte_map.
 238   jbyte* byte_map_base;
 239 
 240   // Return true if "p" is at the start of a card.
 241   bool is_card_aligned(HeapWord* p) {
 242     jbyte* pcard = byte_for(p);
 243     return (addr_for(pcard) == p);
 244   }
 245 
 246   HeapWord* align_to_card_boundary(HeapWord* p) {
 247     jbyte* pcard = byte_for(p + card_size_in_words - 1);
 248     return addr_for(pcard);
 249   }
 250 
 251   // The kinds of precision a CardTableModRefBS may offer.
 252   enum PrecisionStyle {
 253     Precise,
 254     ObjHeadPreciseArray
 255   };
 256 
 257   // Tells what style of precision this card table offers.
 258   PrecisionStyle precision() {
 259     return ObjHeadPreciseArray; // Only one supported for now.
 260   }
 261 
 262   // ModRefBS functions.
 263   virtual void invalidate(MemRegion mr);
 264   void clear(MemRegion mr);
 265   void dirty(MemRegion mr);
 266 
 267   // *** Card-table-RemSet-specific things.
 268 
 269   static uintx ct_max_alignment_constraint();
 270 
 271   // Apply closure "cl" to the dirty cards containing some part of
 272   // MemRegion "mr".
 273   void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
 274 
 275   // Return the MemRegion corresponding to the first maximal run
 276   // of dirty cards lying completely within MemRegion mr.
 277   // If reset is "true", then sets those card table entries to the given
 278   // value.
 279   MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
 280                                          int reset_val);
 281 
 282   // Provide read-only access to the card table array.
 283   const jbyte* byte_for_const(const void* p) const {
 284     return byte_for(p);
 285   }
 286   const jbyte* byte_after_const(const void* p) const {
 287     return byte_after(p);
 288   }
 289 
 290   // Mapping from card marking array entry to address of first word
 291   HeapWord* addr_for(const jbyte* p) const {
 292     assert(p >= _byte_map && p < _byte_map + _byte_map_size,
 293            "out of bounds access to card marking array. p: " PTR_FORMAT
 294                    " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
 295            p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
 296     size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
 297     HeapWord* result = (HeapWord*) (delta << card_shift);
 298     assert(_whole_heap.contains(result),
 299            "Returning result = " PTR_FORMAT " out of bounds of "
 300            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
 301            p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
 302     return result;
 303   }
 304 
 305   // Mapping from address to card marking array index.
 306   size_t index_for(void* p) {
 307     assert(_whole_heap.contains(p),
 308            "Attempt to access p = " PTR_FORMAT " out of bounds of "
 309            " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
 310            p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
 311     return byte_for(p) - _byte_map;
 312   }
 313 
 314   const jbyte* byte_for_index(const size_t card_index) const {
 315     return _byte_map + card_index;
 316   }
 317 
 318   // Print a description of the memory for the barrier set
 319   virtual void print_on(outputStream* st) const;
 320 
 321   void verify();
 322   void verify_guard();
 323 
 324   // val_equals -> it will check that all cards covered by mr equal val
 325   // !val_equals -> it will check that all cards covered by mr do not equal val
 326   void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;
 327   void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
 328   void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
 329 };
 330 
 331 template<>
 332 struct BarrierSet::GetName<CardTableModRefBS> {
 333   static const BarrierSet::Name value = BarrierSet::CardTableModRef;
 334 };
 335 
 336 
 337 #endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP