1 /* 2 * Copyright (c) 2001, 2007, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 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. 8 * 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). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 // The CollectedHeap type requires subtypes to implement a method 26 // "block_start". For some subtypes, notably generational 27 // systems using card-table-based write barriers, the efficiency of this 28 // operation may be important. Implementations of the "BlockOffsetArray" 29 // class may be useful in providing such efficient implementations. 30 // 31 // While generally mirroring the structure of the BOT for GenCollectedHeap, 32 // the following types are tailored more towards G1's uses; these should, 33 // however, be merged back into a common BOT to avoid code duplication 34 // and reduce maintenance overhead. 35 // 36 // G1BlockOffsetTable (abstract) 37 // -- G1BlockOffsetArray (uses G1BlockOffsetSharedArray) 38 // -- G1BlockOffsetArrayContigSpace 39 // 40 // A main impediment to the consolidation of this code might be the 41 // effect of making some of the block_start*() calls non-const as 42 // below. Whether that might adversely affect performance optimizations 43 // that compilers might normally perform in the case of non-G1 44 // collectors needs to be carefully investigated prior to any such 45 // consolidation. 46 47 // Forward declarations 48 class ContiguousSpace; 49 class G1BlockOffsetSharedArray; 50 51 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC { 52 friend class VMStructs; 53 protected: 54 // These members describe the region covered by the table. 55 56 // The space this table is covering. 57 HeapWord* _bottom; // == reserved.start 58 HeapWord* _end; // End of currently allocated region. 59 60 public: 61 // Initialize the table to cover the given space. 62 // The contents of the initial table are undefined. 63 G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) : 64 _bottom(bottom), _end(end) 65 { 66 assert(_bottom <= _end, "arguments out of order"); 67 } 68 69 // Note that the committed size of the covered space may have changed, 70 // so the table size might also wish to change. 71 virtual void resize(size_t new_word_size) = 0; 72 73 virtual void set_bottom(HeapWord* new_bottom) { 74 assert(new_bottom <= _end, "new_bottom > _end"); 75 _bottom = new_bottom; 76 resize(pointer_delta(_end, _bottom)); 77 } 78 79 // Requires "addr" to be contained by a block, and returns the address of 80 // the start of that block. (May have side effects, namely updating of 81 // shared array entries that "point" too far backwards. This can occur, 82 // for example, when LAB allocation is used in a space covered by the 83 // table.) 84 virtual HeapWord* block_start_unsafe(const void* addr) = 0; 85 // Same as above, but does not have any of the possible side effects 86 // discussed above. 87 virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0; 88 89 // Returns the address of the start of the block containing "addr", or 90 // else "null" if it is covered by no block. (May have side effects, 91 // namely updating of shared array entries that "point" too far 92 // backwards. This can occur, for example, when lab allocation is used 93 // in a space covered by the table.) 94 inline HeapWord* block_start(const void* addr); 95 // Same as above, but does not have any of the possible side effects 96 // discussed above. 97 inline HeapWord* block_start_const(const void* addr) const; 98 }; 99 100 // This implementation of "G1BlockOffsetTable" divides the covered region 101 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry 102 // for each such subregion indicates how far back one must go to find the 103 // start of the chunk that includes the first word of the subregion. 104 // 105 // Each BlockOffsetArray is owned by a Space. However, the actual array 106 // may be shared by several BlockOffsetArrays; this is useful 107 // when a single resizable area (such as a generation) is divided up into 108 // several spaces in which contiguous allocation takes place, 109 // such as, for example, in G1 or in the train generation.) 110 111 // Here is the shared array type. 112 113 class G1BlockOffsetSharedArray: public CHeapObj { 114 friend class G1BlockOffsetArray; 115 friend class G1BlockOffsetArrayContigSpace; 116 friend class VMStructs; 117 118 private: 119 // The reserved region covered by the shared array. 120 MemRegion _reserved; 121 122 // End of the current committed region. 123 HeapWord* _end; 124 125 // Array for keeping offsets for retrieving object start fast given an 126 // address. 127 VirtualSpace _vs; 128 u_char* _offset_array; // byte array keeping backwards offsets 129 130 // Bounds checking accessors: 131 // For performance these have to devolve to array accesses in product builds. 132 u_char offset_array(size_t index) const { 133 assert(index < _vs.committed_size(), "index out of range"); 134 return _offset_array[index]; 135 } 136 137 void set_offset_array(size_t index, u_char offset) { 138 assert(index < _vs.committed_size(), "index out of range"); 139 assert(offset <= N_words, "offset too large"); 140 _offset_array[index] = offset; 141 } 142 143 void set_offset_array(size_t index, HeapWord* high, HeapWord* low) { 144 assert(index < _vs.committed_size(), "index out of range"); 145 assert(high >= low, "addresses out of order"); 146 assert(pointer_delta(high, low) <= N_words, "offset too large"); 147 _offset_array[index] = (u_char) pointer_delta(high, low); 148 } 149 150 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) { 151 assert(index_for(right - 1) < _vs.committed_size(), 152 "right address out of range"); 153 assert(left < right, "Heap addresses out of order"); 154 size_t num_cards = pointer_delta(right, left) >> LogN_words; 155 memset(&_offset_array[index_for(left)], offset, num_cards); 156 } 157 158 void set_offset_array(size_t left, size_t right, u_char offset) { 159 assert(right < _vs.committed_size(), "right address out of range"); 160 assert(left <= right, "indexes out of order"); 161 size_t num_cards = right - left + 1; 162 memset(&_offset_array[left], offset, num_cards); 163 } 164 165 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const { 166 assert(index < _vs.committed_size(), "index out of range"); 167 assert(high >= low, "addresses out of order"); 168 assert(pointer_delta(high, low) <= N_words, "offset too large"); 169 assert(_offset_array[index] == pointer_delta(high, low), 170 "Wrong offset"); 171 } 172 173 bool is_card_boundary(HeapWord* p) const; 174 175 // Return the number of slots needed for an offset array 176 // that covers mem_region_words words. 177 // We always add an extra slot because if an object 178 // ends on a card boundary we put a 0 in the next 179 // offset array slot, so we want that slot always 180 // to be reserved. 181 182 size_t compute_size(size_t mem_region_words) { 183 size_t number_of_slots = (mem_region_words / N_words) + 1; 184 return ReservedSpace::page_align_size_up(number_of_slots); 185 } 186 187 public: 188 enum SomePublicConstants { 189 LogN = 9, 190 LogN_words = LogN - LogHeapWordSize, 191 N_bytes = 1 << LogN, 192 N_words = 1 << LogN_words 193 }; 194 195 // Initialize the table to cover from "base" to (at least) 196 // "base + init_word_size". In the future, the table may be expanded 197 // (see "resize" below) up to the size of "_reserved" (which must be at 198 // least "init_word_size".) The contents of the initial table are 199 // undefined; it is the responsibility of the constituent 200 // G1BlockOffsetTable(s) to initialize cards. 201 G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size); 202 203 // Notes a change in the committed size of the region covered by the 204 // table. The "new_word_size" may not be larger than the size of the 205 // reserved region this table covers. 206 void resize(size_t new_word_size); 207 208 void set_bottom(HeapWord* new_bottom); 209 210 // Updates all the BlockOffsetArray's sharing this shared array to 211 // reflect the current "top"'s of their spaces. 212 void update_offset_arrays(); 213 214 // Return the appropriate index into "_offset_array" for "p". 215 inline size_t index_for(const void* p) const; 216 217 // Return the address indicating the start of the region corresponding to 218 // "index" in "_offset_array". 219 inline HeapWord* address_for_index(size_t index) const; 220 }; 221 222 // And here is the G1BlockOffsetTable subtype that uses the array. 223 224 class G1BlockOffsetArray: public G1BlockOffsetTable { 225 friend class G1BlockOffsetSharedArray; 226 friend class G1BlockOffsetArrayContigSpace; 227 friend class VMStructs; 228 private: 229 enum SomePrivateConstants { 230 N_words = G1BlockOffsetSharedArray::N_words, 231 LogN = G1BlockOffsetSharedArray::LogN 232 }; 233 234 // The following enums are used by do_block_helper 235 enum Action { 236 Action_single, // BOT records a single block (see single_block()) 237 Action_mark, // BOT marks the start of a block (see mark_block()) 238 Action_check // Check that BOT records block correctly 239 // (see verify_single_block()). 240 }; 241 242 // This is the array, which can be shared by several BlockOffsetArray's 243 // servicing different 244 G1BlockOffsetSharedArray* _array; 245 246 // The space that owns this subregion. 247 Space* _sp; 248 249 // If "_sp" is a contiguous space, the field below is the view of "_sp" 250 // as a contiguous space, else NULL. 251 ContiguousSpace* _csp; 252 253 // If true, array entries are initialized to 0; otherwise, they are 254 // initialized to point backwards to the beginning of the covered region. 255 bool _init_to_zero; 256 257 // The portion [_unallocated_block, _sp.end()) of the space that 258 // is a single block known not to contain any objects. 259 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag. 260 HeapWord* _unallocated_block; 261 262 // Sets the entries 263 // corresponding to the cards starting at "start" and ending at "end" 264 // to point back to the card before "start": the interval [start, end) 265 // is right-open. 266 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end); 267 // Same as above, except that the args here are a card _index_ interval 268 // that is closed: [start_index, end_index] 269 void set_remainder_to_point_to_start_incl(size_t start, size_t end); 270 271 // A helper function for BOT adjustment/verification work 272 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action); 273 274 protected: 275 276 ContiguousSpace* csp() const { return _csp; } 277 278 // Returns the address of a block whose start is at most "addr". 279 // If "has_max_index" is true, "assumes "max_index" is the last valid one 280 // in the array. 281 inline HeapWord* block_at_or_preceding(const void* addr, 282 bool has_max_index, 283 size_t max_index) const; 284 285 // "q" is a block boundary that is <= "addr"; "n" is the address of the 286 // next block (or the end of the space.) Return the address of the 287 // beginning of the block that contains "addr". Does so without side 288 // effects (see, e.g., spec of block_start.) 289 inline HeapWord* 290 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n, 291 const void* addr) const; 292 293 // "q" is a block boundary that is <= "addr"; return the address of the 294 // beginning of the block that contains "addr". May have side effects 295 // on "this", by updating imprecise entries. 296 inline HeapWord* forward_to_block_containing_addr(HeapWord* q, 297 const void* addr); 298 299 // "q" is a block boundary that is <= "addr"; "n" is the address of the 300 // next block (or the end of the space.) Return the address of the 301 // beginning of the block that contains "addr". May have side effects 302 // on "this", by updating imprecise entries. 303 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q, 304 HeapWord* n, 305 const void* addr); 306 307 // Requires that "*threshold_" be the first array entry boundary at or 308 // above "blk_start", and that "*index_" be the corresponding array 309 // index. If the block starts at or crosses "*threshold_", records 310 // "blk_start" as the appropriate block start for the array index 311 // starting at "*threshold_", and for any other indices crossed by the 312 // block. Updates "*threshold_" and "*index_" to correspond to the first 313 // index after the block end. 314 void alloc_block_work2(HeapWord** threshold_, size_t* index_, 315 HeapWord* blk_start, HeapWord* blk_end); 316 317 public: 318 // The space may not have it's bottom and top set yet, which is why the 319 // region is passed as a parameter. If "init_to_zero" is true, the 320 // elements of the array are initialized to zero. Otherwise, they are 321 // initialized to point backwards to the beginning. 322 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr, 323 bool init_to_zero); 324 325 // Note: this ought to be part of the constructor, but that would require 326 // "this" to be passed as a parameter to a member constructor for 327 // the containing concrete subtype of Space. 328 // This would be legal C++, but MS VC++ doesn't allow it. 329 void set_space(Space* sp); 330 331 // Resets the covered region to the given "mr". 332 void set_region(MemRegion mr); 333 334 // Resets the covered region to one with the same _bottom as before but 335 // the "new_word_size". 336 void resize(size_t new_word_size); 337 338 // These must be guaranteed to work properly (i.e., do nothing) 339 // when "blk_start" ("blk" for second version) is "NULL". 340 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end); 341 virtual void alloc_block(HeapWord* blk, size_t size) { 342 alloc_block(blk, blk + size); 343 } 344 345 // The following methods are useful and optimized for a 346 // general, non-contiguous space. 347 348 // The given arguments are required to be the starts of adjacent ("blk1" 349 // before "blk2") well-formed blocks covered by "this". After this call, 350 // they should be considered to form one block. 351 virtual void join_blocks(HeapWord* blk1, HeapWord* blk2); 352 353 // Given a block [blk_start, blk_start + full_blk_size), and 354 // a left_blk_size < full_blk_size, adjust the BOT to show two 355 // blocks [blk_start, blk_start + left_blk_size) and 356 // [blk_start + left_blk_size, blk_start + full_blk_size). 357 // It is assumed (and verified in the non-product VM) that the 358 // BOT was correct for the original block. 359 void split_block(HeapWord* blk_start, size_t full_blk_size, 360 size_t left_blk_size); 361 362 // Adjust the BOT to show that it has a single block in the 363 // range [blk_start, blk_start + size). All necessary BOT 364 // cards are adjusted, but _unallocated_block isn't. 365 void single_block(HeapWord* blk_start, HeapWord* blk_end); 366 void single_block(HeapWord* blk, size_t size) { 367 single_block(blk, blk + size); 368 } 369 370 // Adjust BOT to show that it has a block in the range 371 // [blk_start, blk_start + size). Only the first card 372 // of BOT is touched. It is assumed (and verified in the 373 // non-product VM) that the remaining cards of the block 374 // are correct. 375 void mark_block(HeapWord* blk_start, HeapWord* blk_end); 376 void mark_block(HeapWord* blk, size_t size) { 377 mark_block(blk, blk + size); 378 } 379 380 // Adjust _unallocated_block to indicate that a particular 381 // block has been newly allocated or freed. It is assumed (and 382 // verified in the non-product VM) that the BOT is correct for 383 // the given block. 384 inline void allocated(HeapWord* blk_start, HeapWord* blk_end) { 385 // Verify that the BOT shows [blk, blk + blk_size) to be one block. 386 verify_single_block(blk_start, blk_end); 387 if (BlockOffsetArrayUseUnallocatedBlock) { 388 _unallocated_block = MAX2(_unallocated_block, blk_end); 389 } 390 } 391 392 inline void allocated(HeapWord* blk, size_t size) { 393 allocated(blk, blk + size); 394 } 395 396 inline void freed(HeapWord* blk_start, HeapWord* blk_end); 397 398 inline void freed(HeapWord* blk, size_t size); 399 400 virtual HeapWord* block_start_unsafe(const void* addr); 401 virtual HeapWord* block_start_unsafe_const(const void* addr) const; 402 403 // Requires "addr" to be the start of a card and returns the 404 // start of the block that contains the given address. 405 HeapWord* block_start_careful(const void* addr) const; 406 407 // If true, initialize array slots with no allocated blocks to zero. 408 // Otherwise, make them point back to the front. 409 bool init_to_zero() { return _init_to_zero; } 410 411 // Verification & debugging - ensure that the offset table reflects the fact 412 // that the block [blk_start, blk_end) or [blk, blk + size) is a 413 // single block of storage. NOTE: can;t const this because of 414 // call to non-const do_block_internal() below. 415 inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) { 416 if (VerifyBlockOffsetArray) { 417 do_block_internal(blk_start, blk_end, Action_check); 418 } 419 } 420 421 inline void verify_single_block(HeapWord* blk, size_t size) { 422 verify_single_block(blk, blk + size); 423 } 424 425 // Verify that the given block is before _unallocated_block 426 inline void verify_not_unallocated(HeapWord* blk_start, 427 HeapWord* blk_end) const { 428 if (BlockOffsetArrayUseUnallocatedBlock) { 429 assert(blk_start < blk_end, "Block inconsistency?"); 430 assert(blk_end <= _unallocated_block, "_unallocated_block problem"); 431 } 432 } 433 434 inline void verify_not_unallocated(HeapWord* blk, size_t size) const { 435 verify_not_unallocated(blk, blk + size); 436 } 437 438 void check_all_cards(size_t left_card, size_t right_card) const; 439 }; 440 441 // A subtype of BlockOffsetArray that takes advantage of the fact 442 // that its underlying space is a ContiguousSpace, so that its "active" 443 // region can be more efficiently tracked (than for a non-contiguous space). 444 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray { 445 friend class VMStructs; 446 447 // allocation boundary at which offset array must be updated 448 HeapWord* _next_offset_threshold; 449 size_t _next_offset_index; // index corresponding to that boundary 450 451 // Work function to be called when allocation start crosses the next 452 // threshold in the contig space. 453 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) { 454 alloc_block_work2(&_next_offset_threshold, &_next_offset_index, 455 blk_start, blk_end); 456 } 457 458 459 public: 460 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr); 461 462 // Initialize the threshold to reflect the first boundary after the 463 // bottom of the covered region. 464 HeapWord* initialize_threshold(); 465 466 // Zero out the entry for _bottom (offset will be zero). 467 void zero_bottom_entry(); 468 469 // Return the next threshold, the point at which the table should be 470 // updated. 471 HeapWord* threshold() const { return _next_offset_threshold; } 472 473 // These must be guaranteed to work properly (i.e., do nothing) 474 // when "blk_start" ("blk" for second version) is "NULL". In this 475 // implementation, that's true because NULL is represented as 0, and thus 476 // never exceeds the "_next_offset_threshold". 477 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) { 478 if (blk_end > _next_offset_threshold) 479 alloc_block_work1(blk_start, blk_end); 480 } 481 void alloc_block(HeapWord* blk, size_t size) { 482 alloc_block(blk, blk+size); 483 } 484 485 HeapWord* block_start_unsafe(const void* addr); 486 HeapWord* block_start_unsafe_const(const void* addr) const; 487 };