1 /*
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  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP
  27 
  28 #include "memory/memRegion.hpp"
  29 #include "runtime/virtualspace.hpp"
  30 #include "utilities/globalDefinitions.hpp"
  31 
  32 // The CollectedHeap type requires subtypes to implement a method
  33 // "block_start".  For some subtypes, notably generational
  34 // systems using card-table-based write barriers, the efficiency of this
  35 // operation may be important.  Implementations of the "BlockOffsetArray"
  36 // class may be useful in providing such efficient implementations.
  37 //
  38 // While generally mirroring the structure of the BOT for GenCollectedHeap,
  39 // the following types are tailored more towards G1's uses; these should,
  40 // however, be merged back into a common BOT to avoid code duplication
  41 // and reduce maintenance overhead.
  42 //
  43 //    G1BlockOffsetTable (abstract)
  44 //    -- G1BlockOffsetArray                (uses G1BlockOffsetSharedArray)
  45 //       -- G1BlockOffsetArrayContigSpace
  46 //
  47 // A main impediment to the consolidation of this code might be the
  48 // effect of making some of the block_start*() calls non-const as
  49 // below. Whether that might adversely affect performance optimizations
  50 // that compilers might normally perform in the case of non-G1
  51 // collectors needs to be carefully investigated prior to any such
  52 // consolidation.
  53 
  54 // Forward declarations
  55 class ContiguousSpace;
  56 class G1BlockOffsetSharedArray;
  57 
  58 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
  59   friend class VMStructs;
  60 protected:
  61   // These members describe the region covered by the table.
  62 
  63   // The space this table is covering.
  64   HeapWord* _bottom;    // == reserved.start
  65   HeapWord* _end;       // End of currently allocated region.
  66 
  67 public:
  68   // Initialize the table to cover the given space.
  69   // The contents of the initial table are undefined.
  70   G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
  71     _bottom(bottom), _end(end)
  72     {
  73       assert(_bottom <= _end, "arguments out of order");
  74     }
  75 
  76   // Note that the committed size of the covered space may have changed,
  77   // so the table size might also wish to change.
  78   virtual void resize(size_t new_word_size) = 0;
  79 
  80   virtual void set_bottom(HeapWord* new_bottom) {
  81     assert(new_bottom <= _end,
  82            err_msg("new_bottom (" PTR_FORMAT ") > _end (" PTR_FORMAT ")",
  83                    p2i(new_bottom), p2i(_end)));
  84     _bottom = new_bottom;
  85     resize(pointer_delta(_end, _bottom));
  86   }
  87 
  88   // Requires "addr" to be contained by a block, and returns the address of
  89   // the start of that block.  (May have side effects, namely updating of
  90   // shared array entries that "point" too far backwards.  This can occur,
  91   // for example, when LAB allocation is used in a space covered by the
  92   // table.)
  93   virtual HeapWord* block_start_unsafe(const void* addr) = 0;
  94   // Same as above, but does not have any of the possible side effects
  95   // discussed above.
  96   virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
  97 
  98   // Returns the address of the start of the block containing "addr", or
  99   // else "null" if it is covered by no block.  (May have side effects,
 100   // namely updating of shared array entries that "point" too far
 101   // backwards.  This can occur, for example, when lab allocation is used
 102   // in a space covered by the table.)
 103   inline HeapWord* block_start(const void* addr);
 104   // Same as above, but does not have any of the possible side effects
 105   // discussed above.
 106   inline HeapWord* block_start_const(const void* addr) const;
 107 };
 108 
 109 // This implementation of "G1BlockOffsetTable" divides the covered region
 110 // into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry
 111 // for each such subregion indicates how far back one must go to find the
 112 // start of the chunk that includes the first word of the subregion.
 113 //
 114 // Each BlockOffsetArray is owned by a Space.  However, the actual array
 115 // may be shared by several BlockOffsetArrays; this is useful
 116 // when a single resizable area (such as a generation) is divided up into
 117 // several spaces in which contiguous allocation takes place,
 118 // such as, for example, in G1 or in the train generation.)
 119 
 120 // Here is the shared array type.
 121 
 122 class G1BlockOffsetSharedArray: public CHeapObj<mtGC> {
 123   friend class G1BlockOffsetArray;
 124   friend class G1BlockOffsetArrayContigSpace;
 125   friend class VMStructs;
 126 
 127 private:
 128   // The reserved region covered by the shared array.
 129   MemRegion _reserved;
 130 
 131   // End of the current committed region.
 132   HeapWord* _end;
 133 
 134   // Array for keeping offsets for retrieving object start fast given an
 135   // address.
 136   VirtualSpace _vs;
 137   u_char* _offset_array;          // byte array keeping backwards offsets
 138 
 139   void check_index(size_t index, const char* msg) const {
 140     assert(index < _vs.committed_size(),
 141            err_msg("%s - "
 142                    "index: " SIZE_FORMAT ", _vs.committed_size: " SIZE_FORMAT,
 143                    msg, index, _vs.committed_size()));
 144   }
 145 
 146   void check_offset(size_t offset, const char* msg) const {
 147     assert(offset <= N_words,
 148            err_msg("%s - "
 149                    "offset: " SIZE_FORMAT", N_words: %u",
 150                    msg, offset, (uint)N_words));
 151   }
 152 
 153   // Bounds checking accessors:
 154   // For performance these have to devolve to array accesses in product builds.
 155   u_char offset_array(size_t index) const {
 156     check_index(index, "index out of range");
 157     return _offset_array[index];
 158   }
 159 
 160   void set_offset_array(size_t index, u_char offset) {
 161     check_index(index, "index out of range");
 162     check_offset(offset, "offset too large");
 163     _offset_array[index] = offset;
 164   }
 165 
 166   void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
 167     check_index(index, "index out of range");
 168     assert(high >= low, "addresses out of order");
 169     check_offset(pointer_delta(high, low), "offset too large");
 170     _offset_array[index] = (u_char) pointer_delta(high, low);
 171   }
 172 
 173   void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
 174     check_index(index_for(right - 1), "right address out of range");
 175     assert(left  < right, "Heap addresses out of order");
 176     size_t num_cards = pointer_delta(right, left) >> LogN_words;
 177     if (UseMemSetInBOT) {
 178       memset(&_offset_array[index_for(left)], offset, num_cards);
 179     } else {
 180       size_t i = index_for(left);
 181       const size_t end = i + num_cards;
 182       for (; i < end; i++) {
 183         _offset_array[i] = offset;
 184       }
 185     }
 186   }
 187 
 188   void set_offset_array(size_t left, size_t right, u_char offset) {
 189     check_index(right, "right index out of range");
 190     assert(left <= right, "indexes out of order");
 191     size_t num_cards = right - left + 1;
 192     if (UseMemSetInBOT) {
 193       memset(&_offset_array[left], offset, num_cards);
 194     } else {
 195       size_t i = left;
 196       const size_t end = i + num_cards;
 197       for (; i < end; i++) {
 198         _offset_array[i] = offset;
 199       }
 200     }
 201   }
 202 
 203   void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
 204     check_index(index, "index out of range");
 205     assert(high >= low, "addresses out of order");
 206     check_offset(pointer_delta(high, low), "offset too large");
 207     assert(_offset_array[index] == pointer_delta(high, low), "Wrong offset");
 208   }
 209 
 210   bool is_card_boundary(HeapWord* p) const;
 211 
 212   // Return the number of slots needed for an offset array
 213   // that covers mem_region_words words.
 214   // We always add an extra slot because if an object
 215   // ends on a card boundary we put a 0 in the next
 216   // offset array slot, so we want that slot always
 217   // to be reserved.
 218 
 219   size_t compute_size(size_t mem_region_words) {
 220     size_t number_of_slots = (mem_region_words / N_words) + 1;
 221     return ReservedSpace::page_align_size_up(number_of_slots);
 222   }
 223 
 224 public:
 225   enum SomePublicConstants {
 226     LogN = 9,
 227     LogN_words = LogN - LogHeapWordSize,
 228     N_bytes = 1 << LogN,
 229     N_words = 1 << LogN_words
 230   };
 231 
 232   // Initialize the table to cover from "base" to (at least)
 233   // "base + init_word_size".  In the future, the table may be expanded
 234   // (see "resize" below) up to the size of "_reserved" (which must be at
 235   // least "init_word_size".) The contents of the initial table are
 236   // undefined; it is the responsibility of the constituent
 237   // G1BlockOffsetTable(s) to initialize cards.
 238   G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
 239 
 240   // Notes a change in the committed size of the region covered by the
 241   // table.  The "new_word_size" may not be larger than the size of the
 242   // reserved region this table covers.
 243   void resize(size_t new_word_size);
 244 
 245   void set_bottom(HeapWord* new_bottom);
 246 
 247   // Updates all the BlockOffsetArray's sharing this shared array to
 248   // reflect the current "top"'s of their spaces.
 249   void update_offset_arrays();
 250 
 251   // Return the appropriate index into "_offset_array" for "p".
 252   inline size_t index_for(const void* p) const;
 253 
 254   // Return the address indicating the start of the region corresponding to
 255   // "index" in "_offset_array".
 256   inline HeapWord* address_for_index(size_t index) const;
 257 };
 258 
 259 // And here is the G1BlockOffsetTable subtype that uses the array.
 260 
 261 class G1BlockOffsetArray: public G1BlockOffsetTable {
 262   friend class G1BlockOffsetSharedArray;
 263   friend class G1BlockOffsetArrayContigSpace;
 264   friend class VMStructs;
 265 private:
 266   enum SomePrivateConstants {
 267     N_words = G1BlockOffsetSharedArray::N_words,
 268     LogN    = G1BlockOffsetSharedArray::LogN
 269   };
 270 
 271   // The following enums are used by do_block_helper
 272   enum Action {
 273     Action_single,      // BOT records a single block (see single_block())
 274     Action_mark,        // BOT marks the start of a block (see mark_block())
 275     Action_check        // Check that BOT records block correctly
 276                         // (see verify_single_block()).
 277   };
 278 
 279   // This is the array, which can be shared by several BlockOffsetArray's
 280   // servicing different
 281   G1BlockOffsetSharedArray* _array;
 282 
 283   // The space that owns this subregion.
 284   Space* _sp;
 285 
 286   // If "_sp" is a contiguous space, the field below is the view of "_sp"
 287   // as a contiguous space, else NULL.
 288   ContiguousSpace* _csp;
 289 
 290   // If true, array entries are initialized to 0; otherwise, they are
 291   // initialized to point backwards to the beginning of the covered region.
 292   bool _init_to_zero;
 293 
 294   // The portion [_unallocated_block, _sp.end()) of the space that
 295   // is a single block known not to contain any objects.
 296   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
 297   HeapWord* _unallocated_block;
 298 
 299   // Sets the entries
 300   // corresponding to the cards starting at "start" and ending at "end"
 301   // to point back to the card before "start": the interval [start, end)
 302   // is right-open.
 303   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
 304   // Same as above, except that the args here are a card _index_ interval
 305   // that is closed: [start_index, end_index]
 306   void set_remainder_to_point_to_start_incl(size_t start, size_t end);
 307 
 308   // A helper function for BOT adjustment/verification work
 309   void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
 310 
 311 protected:
 312 
 313   ContiguousSpace* csp() const { return _csp; }
 314 
 315   // Returns the address of a block whose start is at most "addr".
 316   // If "has_max_index" is true, "assumes "max_index" is the last valid one
 317   // in the array.
 318   inline HeapWord* block_at_or_preceding(const void* addr,
 319                                          bool has_max_index,
 320                                          size_t max_index) const;
 321 
 322   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 323   // next block (or the end of the space.)  Return the address of the
 324   // beginning of the block that contains "addr".  Does so without side
 325   // effects (see, e.g., spec of  block_start.)
 326   inline HeapWord*
 327   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
 328                                          const void* addr) const;
 329 
 330   // "q" is a block boundary that is <= "addr"; return the address of the
 331   // beginning of the block that contains "addr".  May have side effects
 332   // on "this", by updating imprecise entries.
 333   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
 334                                                     const void* addr);
 335 
 336   // "q" is a block boundary that is <= "addr"; "n" is the address of the
 337   // next block (or the end of the space.)  Return the address of the
 338   // beginning of the block that contains "addr".  May have side effects
 339   // on "this", by updating imprecise entries.
 340   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
 341                                                   HeapWord* n,
 342                                                   const void* addr);
 343 
 344   // Requires that "*threshold_" be the first array entry boundary at or
 345   // above "blk_start", and that "*index_" be the corresponding array
 346   // index.  If the block starts at or crosses "*threshold_", records
 347   // "blk_start" as the appropriate block start for the array index
 348   // starting at "*threshold_", and for any other indices crossed by the
 349   // block.  Updates "*threshold_" and "*index_" to correspond to the first
 350   // index after the block end.
 351   void alloc_block_work2(HeapWord** threshold_, size_t* index_,
 352                          HeapWord* blk_start, HeapWord* blk_end);
 353 
 354 public:
 355   // The space may not have it's bottom and top set yet, which is why the
 356   // region is passed as a parameter.  If "init_to_zero" is true, the
 357   // elements of the array are initialized to zero.  Otherwise, they are
 358   // initialized to point backwards to the beginning.
 359   G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
 360                      bool init_to_zero);
 361 
 362   // Note: this ought to be part of the constructor, but that would require
 363   // "this" to be passed as a parameter to a member constructor for
 364   // the containing concrete subtype of Space.
 365   // This would be legal C++, but MS VC++ doesn't allow it.
 366   void set_space(Space* sp);
 367 
 368   // Resets the covered region to the given "mr".
 369   void set_region(MemRegion mr);
 370 
 371   // Resets the covered region to one with the same _bottom as before but
 372   // the "new_word_size".
 373   void resize(size_t new_word_size);
 374 
 375   // These must be guaranteed to work properly (i.e., do nothing)
 376   // when "blk_start" ("blk" for second version) is "NULL".
 377   virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
 378   virtual void alloc_block(HeapWord* blk, size_t size) {
 379     alloc_block(blk, blk + size);
 380   }
 381 
 382   // The following methods are useful and optimized for a
 383   // general, non-contiguous space.
 384 
 385   // Given a block [blk_start, blk_start + full_blk_size), and
 386   // a left_blk_size < full_blk_size, adjust the BOT to show two
 387   // blocks [blk_start, blk_start + left_blk_size) and
 388   // [blk_start + left_blk_size, blk_start + full_blk_size).
 389   // It is assumed (and verified in the non-product VM) that the
 390   // BOT was correct for the original block.
 391   void split_block(HeapWord* blk_start, size_t full_blk_size,
 392                            size_t left_blk_size);
 393 
 394   // Adjust the BOT to show that it has a single block in the
 395   // range [blk_start, blk_start + size). All necessary BOT
 396   // cards are adjusted, but _unallocated_block isn't.
 397   void single_block(HeapWord* blk_start, HeapWord* blk_end);
 398   void single_block(HeapWord* blk, size_t size) {
 399     single_block(blk, blk + size);
 400   }
 401 
 402   // Adjust BOT to show that it has a block in the range
 403   // [blk_start, blk_start + size). Only the first card
 404   // of BOT is touched. It is assumed (and verified in the
 405   // non-product VM) that the remaining cards of the block
 406   // are correct.
 407   void mark_block(HeapWord* blk_start, HeapWord* blk_end);
 408   void mark_block(HeapWord* blk, size_t size) {
 409     mark_block(blk, blk + size);
 410   }
 411 
 412   // Adjust _unallocated_block to indicate that a particular
 413   // block has been newly allocated or freed. It is assumed (and
 414   // verified in the non-product VM) that the BOT is correct for
 415   // the given block.
 416   inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
 417     // Verify that the BOT shows [blk, blk + blk_size) to be one block.
 418     verify_single_block(blk_start, blk_end);
 419     if (BlockOffsetArrayUseUnallocatedBlock) {
 420       _unallocated_block = MAX2(_unallocated_block, blk_end);
 421     }
 422   }
 423 
 424   inline void allocated(HeapWord* blk, size_t size) {
 425     allocated(blk, blk + size);
 426   }
 427 
 428   inline void freed(HeapWord* blk_start, HeapWord* blk_end);
 429 
 430   inline void freed(HeapWord* blk, size_t size);
 431 
 432   virtual HeapWord* block_start_unsafe(const void* addr);
 433   virtual HeapWord* block_start_unsafe_const(const void* addr) const;
 434 
 435   // Requires "addr" to be the start of a card and returns the
 436   // start of the block that contains the given address.
 437   HeapWord* block_start_careful(const void* addr) const;
 438 
 439   // If true, initialize array slots with no allocated blocks to zero.
 440   // Otherwise, make them point back to the front.
 441   bool init_to_zero() { return _init_to_zero; }
 442 
 443   // Verification & debugging - ensure that the offset table reflects the fact
 444   // that the block [blk_start, blk_end) or [blk, blk + size) is a
 445   // single block of storage. NOTE: can;t const this because of
 446   // call to non-const do_block_internal() below.
 447   inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
 448     if (VerifyBlockOffsetArray) {
 449       do_block_internal(blk_start, blk_end, Action_check);
 450     }
 451   }
 452 
 453   inline void verify_single_block(HeapWord* blk, size_t size) {
 454     verify_single_block(blk, blk + size);
 455   }
 456 
 457   // Used by region verification. Checks that the contents of the
 458   // BOT reflect that there's a single object that spans the address
 459   // range [obj_start, obj_start + word_size); returns true if this is
 460   // the case, returns false if it's not.
 461   bool verify_for_object(HeapWord* obj_start, size_t word_size) const;
 462 
 463   // Verify that the given block is before _unallocated_block
 464   inline void verify_not_unallocated(HeapWord* blk_start,
 465                                      HeapWord* blk_end) const {
 466     if (BlockOffsetArrayUseUnallocatedBlock) {
 467       assert(blk_start < blk_end, "Block inconsistency?");
 468       assert(blk_end <= _unallocated_block, "_unallocated_block problem");
 469     }
 470   }
 471 
 472   inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
 473     verify_not_unallocated(blk, blk + size);
 474   }
 475 
 476   void check_all_cards(size_t left_card, size_t right_card) const;
 477 
 478   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 479 };
 480 
 481 // A subtype of BlockOffsetArray that takes advantage of the fact
 482 // that its underlying space is a ContiguousSpace, so that its "active"
 483 // region can be more efficiently tracked (than for a non-contiguous space).
 484 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
 485   friend class VMStructs;
 486 
 487   // allocation boundary at which offset array must be updated
 488   HeapWord* _next_offset_threshold;
 489   size_t    _next_offset_index;      // index corresponding to that boundary
 490 
 491   // Work function to be called when allocation start crosses the next
 492   // threshold in the contig space.
 493   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
 494     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
 495                       blk_start, blk_end);
 496   }
 497 
 498  public:
 499   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
 500 
 501   // Initialize the threshold to reflect the first boundary after the
 502   // bottom of the covered region.
 503   HeapWord* initialize_threshold();
 504 
 505   // Zero out the entry for _bottom (offset will be zero).
 506   void      zero_bottom_entry();
 507 
 508   // Return the next threshold, the point at which the table should be
 509   // updated.
 510   HeapWord* threshold() const { return _next_offset_threshold; }
 511 
 512   // These must be guaranteed to work properly (i.e., do nothing)
 513   // when "blk_start" ("blk" for second version) is "NULL".  In this
 514   // implementation, that's true because NULL is represented as 0, and thus
 515   // never exceeds the "_next_offset_threshold".
 516   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
 517     if (blk_end > _next_offset_threshold)
 518       alloc_block_work1(blk_start, blk_end);
 519   }
 520   void alloc_block(HeapWord* blk, size_t size) {
 521      alloc_block(blk, blk+size);
 522   }
 523 
 524   HeapWord* block_start_unsafe(const void* addr);
 525   HeapWord* block_start_unsafe_const(const void* addr) const;
 526 
 527   void set_for_starts_humongous(HeapWord* new_top);
 528 
 529   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 530 };
 531 
 532 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP