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.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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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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 };