1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 G1BlockOffsetSharedArray;
56 class G1OffsetTableContigSpace;
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 G1OffsetTableContigSpace* _gsp;
285
286 // If true, array entries are initialized to 0; otherwise, they are
287 // initialized to point backwards to the beginning of the covered region.
288 bool _init_to_zero;
289
290 // The portion [_unallocated_block, _sp.end()) of the space that
291 // is a single block known not to contain any objects.
292 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
293 HeapWord* _unallocated_block;
294
295 // Sets the entries
296 // corresponding to the cards starting at "start" and ending at "end"
297 // to point back to the card before "start": the interval [start, end)
298 // is right-open.
299 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
300 // Same as above, except that the args here are a card _index_ interval
301 // that is closed: [start_index, end_index]
302 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
303
304 // A helper function for BOT adjustment/verification work
305 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
306
307 protected:
308
309 G1OffsetTableContigSpace* gsp() const { return _gsp; }
310
311 inline size_t block_size(const HeapWord* p) const;
312
313 // Returns the address of a block whose start is at most "addr".
314 // If "has_max_index" is true, "assumes "max_index" is the last valid one
315 // in the array.
316 inline HeapWord* block_at_or_preceding(const void* addr,
317 bool has_max_index,
318 size_t max_index) const;
319
320 // "q" is a block boundary that is <= "addr"; "n" is the address of the
321 // next block (or the end of the space.) Return the address of the
322 // beginning of the block that contains "addr". Does so without side
323 // effects (see, e.g., spec of block_start.)
324 inline HeapWord*
325 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
326 const void* addr) const;
327
328 // "q" is a block boundary that is <= "addr"; return the address of the
329 // beginning of the block that contains "addr". May have side effects
330 // on "this", by updating imprecise entries.
331 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
332 const void* addr);
333
334 // "q" is a block boundary that is <= "addr"; "n" is the address of the
335 // next block (or the end of the space.) Return the address of the
336 // beginning of the block that contains "addr". May have side effects
337 // on "this", by updating imprecise entries.
338 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
339 HeapWord* n,
340 const void* addr);
341
342 // Requires that "*threshold_" be the first array entry boundary at or
343 // above "blk_start", and that "*index_" be the corresponding array
344 // index. If the block starts at or crosses "*threshold_", records
345 // "blk_start" as the appropriate block start for the array index
346 // starting at "*threshold_", and for any other indices crossed by the
347 // block. Updates "*threshold_" and "*index_" to correspond to the first
348 // index after the block end.
349 void alloc_block_work2(HeapWord** threshold_, size_t* index_,
350 HeapWord* blk_start, HeapWord* blk_end);
351
352 public:
353 // The space may not have it's bottom and top set yet, which is why the
354 // region is passed as a parameter. If "init_to_zero" is true, the
355 // elements of the array are initialized to zero. Otherwise, they are
356 // initialized to point backwards to the beginning.
357 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
358 bool init_to_zero);
359
360 // Note: this ought to be part of the constructor, but that would require
361 // "this" to be passed as a parameter to a member constructor for
362 // the containing concrete subtype of Space.
363 // This would be legal C++, but MS VC++ doesn't allow it.
364 void set_space(G1OffsetTableContigSpace* sp);
365
366 // Resets the covered region to the given "mr".
367 void set_region(MemRegion mr);
368
369 // Resets the covered region to one with the same _bottom as before but
370 // the "new_word_size".
371 void resize(size_t new_word_size);
372
373 // These must be guaranteed to work properly (i.e., do nothing)
374 // when "blk_start" ("blk" for second version) is "NULL".
375 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
376 virtual void alloc_block(HeapWord* blk, size_t size) {
377 alloc_block(blk, blk + size);
378 }
379
380 // The following methods are useful and optimized for a
381 // general, non-contiguous space.
382
383 // Given a block [blk_start, blk_start + full_blk_size), and
384 // a left_blk_size < full_blk_size, adjust the BOT to show two
385 // blocks [blk_start, blk_start + left_blk_size) and
386 // [blk_start + left_blk_size, blk_start + full_blk_size).
387 // It is assumed (and verified in the non-product VM) that the
388 // BOT was correct for the original block.
389 void split_block(HeapWord* blk_start, size_t full_blk_size,
390 size_t left_blk_size);
391
392 // Adjust the BOT to show that it has a single block in the
393 // range [blk_start, blk_start + size). All necessary BOT
394 // cards are adjusted, but _unallocated_block isn't.
395 void single_block(HeapWord* blk_start, HeapWord* blk_end);
396 void single_block(HeapWord* blk, size_t size) {
397 single_block(blk, blk + size);
398 }
399
400 // Adjust BOT to show that it has a block in the range
401 // [blk_start, blk_start + size). Only the first card
402 // of BOT is touched. It is assumed (and verified in the
403 // non-product VM) that the remaining cards of the block
404 // are correct.
405 void mark_block(HeapWord* blk_start, HeapWord* blk_end);
406 void mark_block(HeapWord* blk, size_t size) {
407 mark_block(blk, blk + size);
408 }
409
410 // Adjust _unallocated_block to indicate that a particular
411 // block has been newly allocated or freed. It is assumed (and
412 // verified in the non-product VM) that the BOT is correct for
413 // the given block.
414 inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
415 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
416 verify_single_block(blk_start, blk_end);
417 if (BlockOffsetArrayUseUnallocatedBlock) {
418 _unallocated_block = MAX2(_unallocated_block, blk_end);
419 }
420 }
421
422 inline void allocated(HeapWord* blk, size_t size) {
423 allocated(blk, blk + size);
424 }
425
426 inline void freed(HeapWord* blk_start, HeapWord* blk_end);
427
428 inline void freed(HeapWord* blk, size_t size);
429
430 virtual HeapWord* block_start_unsafe(const void* addr);
431 virtual HeapWord* block_start_unsafe_const(const void* addr) const;
432
433 // Requires "addr" to be the start of a card and returns the
434 // start of the block that contains the given address.
435 HeapWord* block_start_careful(const void* addr) const;
436
437 // If true, initialize array slots with no allocated blocks to zero.
438 // Otherwise, make them point back to the front.
439 bool init_to_zero() { return _init_to_zero; }
440
441 // Verification & debugging - ensure that the offset table reflects the fact
442 // that the block [blk_start, blk_end) or [blk, blk + size) is a
443 // single block of storage. NOTE: can;t const this because of
444 // call to non-const do_block_internal() below.
445 inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
446 if (VerifyBlockOffsetArray) {
447 do_block_internal(blk_start, blk_end, Action_check);
448 }
449 }
450
451 inline void verify_single_block(HeapWord* blk, size_t size) {
452 verify_single_block(blk, blk + size);
453 }
454
455 // Used by region verification. Checks that the contents of the
456 // BOT reflect that there's a single object that spans the address
457 // range [obj_start, obj_start + word_size); returns true if this is
458 // the case, returns false if it's not.
459 bool verify_for_object(HeapWord* obj_start, size_t word_size) const;
460
461 // Verify that the given block is before _unallocated_block
462 inline void verify_not_unallocated(HeapWord* blk_start,
463 HeapWord* blk_end) const {
464 if (BlockOffsetArrayUseUnallocatedBlock) {
465 assert(blk_start < blk_end, "Block inconsistency?");
466 assert(blk_end <= _unallocated_block, "_unallocated_block problem");
467 }
468 }
469
470 inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
471 verify_not_unallocated(blk, blk + size);
472 }
473
474 void check_all_cards(size_t left_card, size_t right_card) const;
475
476 virtual void print_on(outputStream* out) PRODUCT_RETURN;
477 };
478
479 // A subtype of BlockOffsetArray that takes advantage of the fact
480 // that its underlying space is a ContiguousSpace, so that its "active"
481 // region can be more efficiently tracked (than for a non-contiguous space).
482 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
483 friend class VMStructs;
484
485 // allocation boundary at which offset array must be updated
486 HeapWord* _next_offset_threshold;
487 size_t _next_offset_index; // index corresponding to that boundary
488
489 // Work function to be called when allocation start crosses the next
490 // threshold in the contig space.
491 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
492 alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
493 blk_start, blk_end);
494 }
495
496 public:
497 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
498
499 // Initialize the threshold to reflect the first boundary after the
500 // bottom of the covered region.
501 HeapWord* initialize_threshold();
502
503 // Zero out the entry for _bottom (offset will be zero).
504 void zero_bottom_entry();
505
506 // Return the next threshold, the point at which the table should be
507 // updated.
508 HeapWord* threshold() const { return _next_offset_threshold; }
509
510 // These must be guaranteed to work properly (i.e., do nothing)
511 // when "blk_start" ("blk" for second version) is "NULL". In this
512 // implementation, that's true because NULL is represented as 0, and thus
513 // never exceeds the "_next_offset_threshold".
514 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
515 if (blk_end > _next_offset_threshold)
516 alloc_block_work1(blk_start, blk_end);
517 }
518 void alloc_block(HeapWord* blk, size_t size) {
519 alloc_block(blk, blk+size);
520 }
521
522 HeapWord* block_start_unsafe(const void* addr);
523 HeapWord* block_start_unsafe_const(const void* addr) const;
524
525 void set_for_starts_humongous(HeapWord* new_top);
526
527 virtual void print_on(outputStream* out) PRODUCT_RETURN;
528 };
529
530 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP