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 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(HeapWord* left, HeapWord* right, u_char offset);
161
162 void set_offset_array(size_t index, u_char offset) {
163 check_index(index, "index out of range");
164 check_offset(offset, "offset too large");
165 _offset_array[index] = offset;
166 }
167
168 void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
169 check_index(index, "index out of range");
170 assert(high >= low, "addresses out of order");
171 check_offset(pointer_delta(high, low), "offset too large");
172 _offset_array[index] = (u_char) pointer_delta(high, low);
173 }
174
175 void set_offset_array(size_t left, size_t right, u_char offset) {
176 check_index(right, "right index out of range");
177 assert(left <= right, "indexes out of order");
178 size_t num_cards = right - left + 1;
179 if (UseMemSetInBOT) {
180 memset(&_offset_array[left], offset, num_cards);
181 } else {
182 size_t i = left;
183 const size_t end = i + num_cards;
184 for (; i < end; i++) {
185 _offset_array[i] = offset;
186 }
187 }
188 }
189
190 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
191 check_index(index, "index out of range");
192 assert(high >= low, "addresses out of order");
193 check_offset(pointer_delta(high, low), "offset too large");
194 assert(_offset_array[index] == pointer_delta(high, low), "Wrong offset");
195 }
196
197 bool is_card_boundary(HeapWord* p) const;
198
199 // Return the number of slots needed for an offset array
200 // that covers mem_region_words words.
201 // We always add an extra slot because if an object
202 // ends on a card boundary we put a 0 in the next
203 // offset array slot, so we want that slot always
204 // to be reserved.
205
206 size_t compute_size(size_t mem_region_words) {
207 size_t number_of_slots = (mem_region_words / N_words) + 1;
208 return ReservedSpace::page_align_size_up(number_of_slots);
209 }
210
211 public:
212 enum SomePublicConstants {
213 LogN = 9,
214 LogN_words = LogN - LogHeapWordSize,
215 N_bytes = 1 << LogN,
216 N_words = 1 << LogN_words
217 };
218
219 // Initialize the table to cover from "base" to (at least)
220 // "base + init_word_size". In the future, the table may be expanded
221 // (see "resize" below) up to the size of "_reserved" (which must be at
222 // least "init_word_size".) The contents of the initial table are
223 // undefined; it is the responsibility of the constituent
224 // G1BlockOffsetTable(s) to initialize cards.
225 G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
226
227 // Notes a change in the committed size of the region covered by the
228 // table. The "new_word_size" may not be larger than the size of the
229 // reserved region this table covers.
230 void resize(size_t new_word_size);
231
232 void set_bottom(HeapWord* new_bottom);
233
234 // Updates all the BlockOffsetArray's sharing this shared array to
235 // reflect the current "top"'s of their spaces.
236 void update_offset_arrays();
237
238 // Return the appropriate index into "_offset_array" for "p".
239 inline size_t index_for(const void* p) const;
240
241 // Return the address indicating the start of the region corresponding to
242 // "index" in "_offset_array".
243 inline HeapWord* address_for_index(size_t index) const;
244 };
245
246 // And here is the G1BlockOffsetTable subtype that uses the array.
247
248 class G1BlockOffsetArray: public G1BlockOffsetTable {
249 friend class G1BlockOffsetSharedArray;
250 friend class G1BlockOffsetArrayContigSpace;
251 friend class VMStructs;
252 private:
253 enum SomePrivateConstants {
254 N_words = G1BlockOffsetSharedArray::N_words,
255 LogN = G1BlockOffsetSharedArray::LogN
256 };
257
258 // The following enums are used by do_block_helper
259 enum Action {
260 Action_single, // BOT records a single block (see single_block())
261 Action_mark, // BOT marks the start of a block (see mark_block())
262 Action_check // Check that BOT records block correctly
263 // (see verify_single_block()).
264 };
265
266 // This is the array, which can be shared by several BlockOffsetArray's
267 // servicing different
268 G1BlockOffsetSharedArray* _array;
269
270 // The space that owns this subregion.
271 G1OffsetTableContigSpace* _gsp;
272
273 // If true, array entries are initialized to 0; otherwise, they are
274 // initialized to point backwards to the beginning of the covered region.
275 bool _init_to_zero;
276
277 // The portion [_unallocated_block, _sp.end()) of the space that
278 // is a single block known not to contain any objects.
279 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
280 HeapWord* _unallocated_block;
281
282 // Sets the entries
283 // corresponding to the cards starting at "start" and ending at "end"
284 // to point back to the card before "start": the interval [start, end)
285 // is right-open.
286 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
287 // Same as above, except that the args here are a card _index_ interval
288 // that is closed: [start_index, end_index]
289 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
290
291 // A helper function for BOT adjustment/verification work
292 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
293
294 protected:
295
296 G1OffsetTableContigSpace* gsp() const { return _gsp; }
297
298 inline size_t block_size(const HeapWord* p) const;
299
300 // Returns the address of a block whose start is at most "addr".
301 // If "has_max_index" is true, "assumes "max_index" is the last valid one
302 // in the array.
303 inline HeapWord* block_at_or_preceding(const void* addr,
304 bool has_max_index,
305 size_t max_index) const;
306
307 // "q" is a block boundary that is <= "addr"; "n" is the address of the
308 // next block (or the end of the space.) Return the address of the
309 // beginning of the block that contains "addr". Does so without side
310 // effects (see, e.g., spec of block_start.)
311 inline HeapWord*
312 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
313 const void* addr) const;
314
315 // "q" is a block boundary that is <= "addr"; return the address of the
316 // beginning of the block that contains "addr". May have side effects
317 // on "this", by updating imprecise entries.
318 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
319 const void* addr);
320
321 // "q" is a block boundary that is <= "addr"; "n" is the address of the
322 // next block (or the end of the space.) Return the address of the
323 // beginning of the block that contains "addr". May have side effects
324 // on "this", by updating imprecise entries.
325 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
326 HeapWord* n,
327 const void* addr);
328
329 // Requires that "*threshold_" be the first array entry boundary at or
330 // above "blk_start", and that "*index_" be the corresponding array
331 // index. If the block starts at or crosses "*threshold_", records
332 // "blk_start" as the appropriate block start for the array index
333 // starting at "*threshold_", and for any other indices crossed by the
334 // block. Updates "*threshold_" and "*index_" to correspond to the first
335 // index after the block end.
336 void alloc_block_work2(HeapWord** threshold_, size_t* index_,
337 HeapWord* blk_start, HeapWord* blk_end);
338
339 public:
340 // The space may not have it's bottom and top set yet, which is why the
341 // region is passed as a parameter. If "init_to_zero" is true, the
342 // elements of the array are initialized to zero. Otherwise, they are
343 // initialized to point backwards to the beginning.
344 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
345 bool init_to_zero);
346
347 // Note: this ought to be part of the constructor, but that would require
348 // "this" to be passed as a parameter to a member constructor for
349 // the containing concrete subtype of Space.
350 // This would be legal C++, but MS VC++ doesn't allow it.
351 void set_space(G1OffsetTableContigSpace* sp);
352
353 // Resets the covered region to the given "mr".
354 void set_region(MemRegion mr);
355
356 // Resets the covered region to one with the same _bottom as before but
357 // the "new_word_size".
358 void resize(size_t new_word_size);
359
360 // These must be guaranteed to work properly (i.e., do nothing)
361 // when "blk_start" ("blk" for second version) is "NULL".
362 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
363 virtual void alloc_block(HeapWord* blk, size_t size) {
364 alloc_block(blk, blk + size);
365 }
366
367 // The following methods are useful and optimized for a
368 // general, non-contiguous space.
369
370 // Given a block [blk_start, blk_start + full_blk_size), and
371 // a left_blk_size < full_blk_size, adjust the BOT to show two
372 // blocks [blk_start, blk_start + left_blk_size) and
373 // [blk_start + left_blk_size, blk_start + full_blk_size).
374 // It is assumed (and verified in the non-product VM) that the
375 // BOT was correct for the original block.
376 void split_block(HeapWord* blk_start, size_t full_blk_size,
377 size_t left_blk_size);
378
379 // Adjust the BOT to show that it has a single block in the
380 // range [blk_start, blk_start + size). All necessary BOT
381 // cards are adjusted, but _unallocated_block isn't.
382 void single_block(HeapWord* blk_start, HeapWord* blk_end);
383 void single_block(HeapWord* blk, size_t size) {
384 single_block(blk, blk + size);
385 }
386
387 // Adjust BOT to show that it has a block in the range
388 // [blk_start, blk_start + size). Only the first card
389 // of BOT is touched. It is assumed (and verified in the
390 // non-product VM) that the remaining cards of the block
391 // are correct.
392 void mark_block(HeapWord* blk_start, HeapWord* blk_end);
393 void mark_block(HeapWord* blk, size_t size) {
394 mark_block(blk, blk + size);
395 }
396
397 // Adjust _unallocated_block to indicate that a particular
398 // block has been newly allocated or freed. It is assumed (and
399 // verified in the non-product VM) that the BOT is correct for
400 // the given block.
401 inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
402 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
403 verify_single_block(blk_start, blk_end);
404 if (BlockOffsetArrayUseUnallocatedBlock) {
405 _unallocated_block = MAX2(_unallocated_block, blk_end);
406 }
407 }
408
409 inline void allocated(HeapWord* blk, size_t size) {
410 allocated(blk, blk + size);
411 }
412
413 inline void freed(HeapWord* blk_start, HeapWord* blk_end);
414
415 inline void freed(HeapWord* blk, size_t size);
416
417 virtual HeapWord* block_start_unsafe(const void* addr);
418 virtual HeapWord* block_start_unsafe_const(const void* addr) const;
419
420 // Requires "addr" to be the start of a card and returns the
421 // start of the block that contains the given address.
422 HeapWord* block_start_careful(const void* addr) const;
423
424 // If true, initialize array slots with no allocated blocks to zero.
425 // Otherwise, make them point back to the front.
426 bool init_to_zero() { return _init_to_zero; }
427
428 // Verification & debugging - ensure that the offset table reflects the fact
429 // that the block [blk_start, blk_end) or [blk, blk + size) is a
430 // single block of storage. NOTE: can;t const this because of
431 // call to non-const do_block_internal() below.
432 inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
433 if (VerifyBlockOffsetArray) {
434 do_block_internal(blk_start, blk_end, Action_check);
435 }
436 }
437
438 inline void verify_single_block(HeapWord* blk, size_t size) {
439 verify_single_block(blk, blk + size);
440 }
441
442 // Used by region verification. Checks that the contents of the
443 // BOT reflect that there's a single object that spans the address
444 // range [obj_start, obj_start + word_size); returns true if this is
445 // the case, returns false if it's not.
446 bool verify_for_object(HeapWord* obj_start, size_t word_size) const;
447
448 // Verify that the given block is before _unallocated_block
449 inline void verify_not_unallocated(HeapWord* blk_start,
450 HeapWord* blk_end) const {
451 if (BlockOffsetArrayUseUnallocatedBlock) {
452 assert(blk_start < blk_end, "Block inconsistency?");
453 assert(blk_end <= _unallocated_block, "_unallocated_block problem");
454 }
455 }
456
457 inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
458 verify_not_unallocated(blk, blk + size);
459 }
460
461 void check_all_cards(size_t left_card, size_t right_card) const;
462
463 virtual void print_on(outputStream* out) PRODUCT_RETURN;
464 };
465
466 // A subtype of BlockOffsetArray that takes advantage of the fact
467 // that its underlying space is a ContiguousSpace, so that its "active"
468 // region can be more efficiently tracked (than for a non-contiguous space).
469 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
470 friend class VMStructs;
471
472 // allocation boundary at which offset array must be updated
473 HeapWord* _next_offset_threshold;
474 size_t _next_offset_index; // index corresponding to that boundary
475
476 // Work function to be called when allocation start crosses the next
477 // threshold in the contig space.
478 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
479 alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
480 blk_start, blk_end);
481 }
482
483 public:
484 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
485
486 // Initialize the threshold to reflect the first boundary after the
487 // bottom of the covered region.
488 HeapWord* initialize_threshold();
489
490 // Zero out the entry for _bottom (offset will be zero).
491 void zero_bottom_entry();
492
493 // Return the next threshold, the point at which the table should be
494 // updated.
495 HeapWord* threshold() const { return _next_offset_threshold; }
496
497 // These must be guaranteed to work properly (i.e., do nothing)
498 // when "blk_start" ("blk" for second version) is "NULL". In this
499 // implementation, that's true because NULL is represented as 0, and thus
500 // never exceeds the "_next_offset_threshold".
501 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
502 if (blk_end > _next_offset_threshold)
503 alloc_block_work1(blk_start, blk_end);
504 }
505 void alloc_block(HeapWord* blk, size_t size) {
506 alloc_block(blk, blk+size);
507 }
508
509 HeapWord* block_start_unsafe(const void* addr);
510 HeapWord* block_start_unsafe_const(const void* addr) const;
511
512 void set_for_starts_humongous(HeapWord* new_top);
513
514 virtual void print_on(outputStream* out) PRODUCT_RETURN;
515 };
516
517 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP