1 /*
2 * Copyright (c) 2000, 2009, 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
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
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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).
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23 */
24
25 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
26 // enumerate ref fields that have been modified (since the last
27 // enumeration.)
28
29 // As it currently stands, this barrier is *imprecise*: when a ref field in
30 // an object "o" is modified, the card table entry for the card containing
31 // the head of "o" is dirtied, not necessarily the card containing the
32 // modified field itself. For object arrays, however, the barrier *is*
33 // precise; only the card containing the modified element is dirtied.
34 // Any MemRegionClosures used to scan dirty cards should take these
35 // considerations into account.
36
37 class Generation;
38 class OopsInGenClosure;
39 class DirtyCardToOopClosure;
40
41 class CardTableModRefBS: public ModRefBarrierSet {
42 // Some classes get to look at some private stuff.
43 friend class BytecodeInterpreter;
44 friend class VMStructs;
45 friend class CardTableRS;
46 friend class CheckForUnmarkedOops; // Needs access to raw card bytes.
47 #ifndef PRODUCT
48 // For debugging.
49 friend class GuaranteeNotModClosure;
50 #endif
51 protected:
52
53 enum CardValues {
54 clean_card = -1,
55 // The mask contains zeros in places for all other values.
56 clean_card_mask = clean_card - 31,
57
58 dirty_card = 0,
59 precleaned_card = 1,
60 claimed_card = 2,
61 deferred_card = 4,
62 last_card = 8,
63 CT_MR_BS_last_reserved = 16
64 };
65
66 // dirty and precleaned are equivalent wrt younger_refs_iter.
67 static bool card_is_dirty_wrt_gen_iter(jbyte cv) {
68 return cv == dirty_card || cv == precleaned_card;
69 }
70
71 // Returns "true" iff the value "cv" will cause the card containing it
72 // to be scanned in the current traversal. May be overridden by
73 // subtypes.
74 virtual bool card_will_be_scanned(jbyte cv) {
75 return CardTableModRefBS::card_is_dirty_wrt_gen_iter(cv);
76 }
77
78 // Returns "true" iff the value "cv" may have represented a dirty card at
79 // some point.
80 virtual bool card_may_have_been_dirty(jbyte cv) {
81 return card_is_dirty_wrt_gen_iter(cv);
82 }
83
84 // The declaration order of these const fields is important; see the
85 // constructor before changing.
86 const MemRegion _whole_heap; // the region covered by the card table
87 const size_t _guard_index; // index of very last element in the card
88 // table; it is set to a guard value
89 // (last_card) and should never be modified
90 const size_t _last_valid_index; // index of the last valid element
91 const size_t _page_size; // page size used when mapping _byte_map
92 const size_t _byte_map_size; // in bytes
93 jbyte* _byte_map; // the card marking array
94
95 int _cur_covered_regions;
96 // The covered regions should be in address order.
97 MemRegion* _covered;
98 // The committed regions correspond one-to-one to the covered regions.
99 // They represent the card-table memory that has been committed to service
100 // the corresponding covered region. It may be that committed region for
101 // one covered region corresponds to a larger region because of page-size
102 // roundings. Thus, a committed region for one covered region may
103 // actually extend onto the card-table space for the next covered region.
104 MemRegion* _committed;
105
106 // The last card is a guard card, and we commit the page for it so
107 // we can use the card for verification purposes. We make sure we never
108 // uncommit the MemRegion for that page.
109 MemRegion _guard_region;
110
111 protected:
112 // Initialization utilities; covered_words is the size of the covered region
113 // in, um, words.
114 inline size_t cards_required(size_t covered_words);
115 inline size_t compute_byte_map_size();
116
117 // Finds and return the index of the region, if any, to which the given
118 // region would be contiguous. If none exists, assign a new region and
119 // returns its index. Requires that no more than the maximum number of
120 // covered regions defined in the constructor are ever in use.
121 int find_covering_region_by_base(HeapWord* base);
122
123 // Same as above, but finds the region containing the given address
124 // instead of starting at a given base address.
125 int find_covering_region_containing(HeapWord* addr);
126
127 // Resize one of the regions covered by the remembered set.
128 void resize_covered_region(MemRegion new_region);
129
130 // Returns the leftmost end of a committed region corresponding to a
131 // covered region before covered region "ind", or else "NULL" if "ind" is
132 // the first covered region.
133 HeapWord* largest_prev_committed_end(int ind) const;
134
135 // Returns the part of the region mr that doesn't intersect with
136 // any committed region other than self. Used to prevent uncommitting
137 // regions that are also committed by other regions. Also protects
138 // against uncommitting the guard region.
139 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
140
141 // Mapping from address to card marking array entry
142 jbyte* byte_for(const void* p) const {
143 assert(_whole_heap.contains(p),
144 "out of bounds access to card marking array");
145 jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
146 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
147 "out of bounds accessor for card marking array");
148 return result;
149 }
150
151 // The card table byte one after the card marking array
152 // entry for argument address. Typically used for higher bounds
153 // for loops iterating through the card table.
154 jbyte* byte_after(const void* p) const {
155 return byte_for(p) + 1;
156 }
157
158 // Iterate over the portion of the card-table which covers the given
159 // region mr in the given space and apply cl to any dirty sub-regions
160 // of mr. cl and dcto_cl must either be the same closure or cl must
161 // wrap dcto_cl. Both are required - neither may be NULL. Also, dcto_cl
162 // may be modified. Note that this function will operate in a parallel
163 // mode if worker threads are available.
164 void non_clean_card_iterate(Space* sp, MemRegion mr,
165 DirtyCardToOopClosure* dcto_cl,
166 MemRegionClosure* cl,
167 bool clear);
168
169 // Utility function used to implement the other versions below.
170 void non_clean_card_iterate_work(MemRegion mr, MemRegionClosure* cl,
171 bool clear);
172
173 void par_non_clean_card_iterate_work(Space* sp, MemRegion mr,
174 DirtyCardToOopClosure* dcto_cl,
175 MemRegionClosure* cl,
176 bool clear,
177 int n_threads);
178
179 // Dirty the bytes corresponding to "mr" (not all of which must be
180 // covered.)
181 void dirty_MemRegion(MemRegion mr);
182
183 // Clear (to clean_card) the bytes entirely contained within "mr" (not
184 // all of which must be covered.)
185 void clear_MemRegion(MemRegion mr);
186
187 // *** Support for parallel card scanning.
188
189 enum SomeConstantsForParallelism {
190 StridesPerThread = 2,
191 CardsPerStrideChunk = 256
192 };
193
194 // This is an array, one element per covered region of the card table.
195 // Each entry is itself an array, with one element per chunk in the
196 // covered region. Each entry of these arrays is the lowest non-clean
197 // card of the corresponding chunk containing part of an object from the
198 // previous chunk, or else NULL.
199 typedef jbyte* CardPtr;
200 typedef CardPtr* CardArr;
201 CardArr* _lowest_non_clean;
202 size_t* _lowest_non_clean_chunk_size;
203 uintptr_t* _lowest_non_clean_base_chunk_index;
204 int* _last_LNC_resizing_collection;
205
206 // Initializes "lowest_non_clean" to point to the array for the region
207 // covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk
208 // index of the corresponding to the first element of that array.
209 // Ensures that these arrays are of sufficient size, allocating if necessary.
210 // May be called by several threads concurrently.
211 void get_LNC_array_for_space(Space* sp,
212 jbyte**& lowest_non_clean,
213 uintptr_t& lowest_non_clean_base_chunk_index,
214 size_t& lowest_non_clean_chunk_size);
215
216 // Returns the number of chunks necessary to cover "mr".
217 size_t chunks_to_cover(MemRegion mr) {
218 return (size_t)(addr_to_chunk_index(mr.last()) -
219 addr_to_chunk_index(mr.start()) + 1);
220 }
221
222 // Returns the index of the chunk in a stride which
223 // covers the given address.
224 uintptr_t addr_to_chunk_index(const void* addr) {
225 uintptr_t card = (uintptr_t) byte_for(addr);
226 return card / CardsPerStrideChunk;
227 }
228
229 // Apply cl, which must either itself apply dcto_cl or be dcto_cl,
230 // to the cards in the stride (of n_strides) within the given space.
231 void process_stride(Space* sp,
232 MemRegion used,
233 jint stride, int n_strides,
234 DirtyCardToOopClosure* dcto_cl,
235 MemRegionClosure* cl,
236 bool clear,
237 jbyte** lowest_non_clean,
238 uintptr_t lowest_non_clean_base_chunk_index,
239 size_t lowest_non_clean_chunk_size);
240
241 // Makes sure that chunk boundaries are handled appropriately, by
242 // adjusting the min_done of dcto_cl, and by using a special card-table
243 // value to indicate how min_done should be set.
244 void process_chunk_boundaries(Space* sp,
245 DirtyCardToOopClosure* dcto_cl,
246 MemRegion chunk_mr,
247 MemRegion used,
248 jbyte** lowest_non_clean,
249 uintptr_t lowest_non_clean_base_chunk_index,
250 size_t lowest_non_clean_chunk_size);
251
252 public:
253 // Constants
254 enum SomePublicConstants {
255 card_shift = 9,
256 card_size = 1 << card_shift,
257 card_size_in_words = card_size / sizeof(HeapWord)
258 };
259
260 static int clean_card_val() { return clean_card; }
261 static int clean_card_mask_val() { return clean_card_mask; }
262 static int dirty_card_val() { return dirty_card; }
263 static int claimed_card_val() { return claimed_card; }
264 static int precleaned_card_val() { return precleaned_card; }
265 static int deferred_card_val() { return deferred_card; }
266
267 // For RTTI simulation.
268 bool is_a(BarrierSet::Name bsn) {
269 return bsn == BarrierSet::CardTableModRef || ModRefBarrierSet::is_a(bsn);
270 }
271
272 CardTableModRefBS(MemRegion whole_heap, int max_covered_regions);
273
274 // *** Barrier set functions.
275
276 bool has_write_ref_pre_barrier() { return false; }
277
278 inline bool write_ref_needs_barrier(void* field, oop new_val) {
279 // Note that this assumes the perm gen is the highest generation
280 // in the address space
281 return new_val != NULL && !new_val->is_perm();
282 }
283
284 // Record a reference update. Note that these versions are precise!
285 // The scanning code has to handle the fact that the write barrier may be
286 // either precise or imprecise. We make non-virtual inline variants of
287 // these functions here for performance.
288 protected:
289 void write_ref_field_work(oop obj, size_t offset, oop newVal);
290 virtual void write_ref_field_work(void* field, oop newVal);
291 public:
292
293 bool has_write_ref_array_opt() { return true; }
294 bool has_write_region_opt() { return true; }
295
296 inline void inline_write_region(MemRegion mr) {
297 dirty_MemRegion(mr);
298 }
299 protected:
300 void write_region_work(MemRegion mr) {
301 inline_write_region(mr);
302 }
303 public:
304
305 inline void inline_write_ref_array(MemRegion mr) {
306 dirty_MemRegion(mr);
307 }
308 protected:
309 void write_ref_array_work(MemRegion mr) {
310 inline_write_ref_array(mr);
311 }
312 public:
313
314 bool is_aligned(HeapWord* addr) {
315 return is_card_aligned(addr);
316 }
317
318 // *** Card-table-barrier-specific things.
319
320 template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}
321
322 template <class T> inline void inline_write_ref_field(T* field, oop newVal) {
323 jbyte* byte = byte_for((void*)field);
324 *byte = dirty_card;
325 }
326
327 // These are used by G1, when it uses the card table as a temporary data
328 // structure for card claiming.
329 bool is_card_dirty(size_t card_index) {
330 return _byte_map[card_index] == dirty_card_val();
331 }
332
333 void mark_card_dirty(size_t card_index) {
334 _byte_map[card_index] = dirty_card_val();
335 }
336
337 bool is_card_claimed(size_t card_index) {
338 jbyte val = _byte_map[card_index];
339 return (val & (clean_card_mask_val() | claimed_card_val())) == claimed_card_val();
340 }
341
342 void set_card_claimed(size_t card_index) {
343 jbyte val = _byte_map[card_index];
344 if (val == clean_card_val()) {
345 val = (jbyte)claimed_card_val();
346 } else {
347 val |= (jbyte)claimed_card_val();
348 }
349 _byte_map[card_index] = val;
350 }
351
352 bool claim_card(size_t card_index);
353
354 bool is_card_clean(size_t card_index) {
355 return _byte_map[card_index] == clean_card_val();
356 }
357
358 bool is_card_deferred(size_t card_index) {
359 jbyte val = _byte_map[card_index];
360 return (val & (clean_card_mask_val() | deferred_card_val())) == deferred_card_val();
361 }
362
363 bool mark_card_deferred(size_t card_index);
364
365 // Card marking array base (adjusted for heap low boundary)
366 // This would be the 0th element of _byte_map, if the heap started at 0x0.
367 // But since the heap starts at some higher address, this points to somewhere
368 // before the beginning of the actual _byte_map.
369 jbyte* byte_map_base;
370
371 // Return true if "p" is at the start of a card.
372 bool is_card_aligned(HeapWord* p) {
373 jbyte* pcard = byte_for(p);
374 return (addr_for(pcard) == p);
375 }
376
377 // The kinds of precision a CardTableModRefBS may offer.
378 enum PrecisionStyle {
379 Precise,
380 ObjHeadPreciseArray
381 };
382
383 // Tells what style of precision this card table offers.
384 PrecisionStyle precision() {
385 return ObjHeadPreciseArray; // Only one supported for now.
386 }
387
388 // ModRefBS functions.
389 virtual void invalidate(MemRegion mr, bool whole_heap = false);
390 void clear(MemRegion mr);
391 void dirty(MemRegion mr);
392 void mod_oop_in_space_iterate(Space* sp, OopClosure* cl,
393 bool clear = false,
394 bool before_save_marks = false);
395
396 // *** Card-table-RemSet-specific things.
397
398 // Invoke "cl.do_MemRegion" on a set of MemRegions that collectively
399 // includes all the modified cards (expressing each card as a
400 // MemRegion). Thus, several modified cards may be lumped into one
401 // region. The regions are non-overlapping, and are visited in
402 // *decreasing* address order. (This order aids with imprecise card
403 // marking, where a dirty card may cause scanning, and summarization
404 // marking, of objects that extend onto subsequent cards.)
405 // If "clear" is true, the card is (conceptually) marked unmodified before
406 // applying the closure.
407 void mod_card_iterate(MemRegionClosure* cl, bool clear = false) {
408 non_clean_card_iterate_work(_whole_heap, cl, clear);
409 }
410
411 // Like the "mod_cards_iterate" above, except only invokes the closure
412 // for cards within the MemRegion "mr" (which is required to be
413 // card-aligned and sized.)
414 void mod_card_iterate(MemRegion mr, MemRegionClosure* cl,
415 bool clear = false) {
416 non_clean_card_iterate_work(mr, cl, clear);
417 }
418
419 static uintx ct_max_alignment_constraint();
420
421 // Apply closure "cl" to the dirty cards containing some part of
422 // MemRegion "mr".
423 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
424
425 // Return the MemRegion corresponding to the first maximal run
426 // of dirty cards lying completely within MemRegion mr.
427 // If reset is "true", then sets those card table entries to the given
428 // value.
429 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
430 int reset_val);
431
432 // Set all the dirty cards in the given region to precleaned state.
433 void preclean_dirty_cards(MemRegion mr);
434
435 // Provide read-only access to the card table array.
436 const jbyte* byte_for_const(const void* p) const {
437 return byte_for(p);
438 }
439 const jbyte* byte_after_const(const void* p) const {
440 return byte_after(p);
441 }
442
443 // Mapping from card marking array entry to address of first word
444 HeapWord* addr_for(const jbyte* p) const {
445 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
446 "out of bounds access to card marking array");
447 size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
448 HeapWord* result = (HeapWord*) (delta << card_shift);
449 assert(_whole_heap.contains(result),
450 "out of bounds accessor from card marking array");
451 return result;
452 }
453
454 // Mapping from address to card marking array index.
455 size_t index_for(void* p) {
456 assert(_whole_heap.contains(p),
457 "out of bounds access to card marking array");
458 return byte_for(p) - _byte_map;
459 }
460
461 const jbyte* byte_for_index(const size_t card_index) const {
462 return _byte_map + card_index;
463 }
464
465 void verify();
466 void verify_guard();
467
468 void verify_clean_region(MemRegion mr) PRODUCT_RETURN;
469 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
470
471 static size_t par_chunk_heapword_alignment() {
472 return CardsPerStrideChunk * card_size_in_words;
473 }
474
475 };
476
477 class CardTableRS;
478
479 // A specialization for the CardTableRS gen rem set.
480 class CardTableModRefBSForCTRS: public CardTableModRefBS {
481 CardTableRS* _rs;
482 protected:
483 bool card_will_be_scanned(jbyte cv);
484 bool card_may_have_been_dirty(jbyte cv);
485 public:
486 CardTableModRefBSForCTRS(MemRegion whole_heap,
487 int max_covered_regions) :
488 CardTableModRefBS(whole_heap, max_covered_regions) {}
489
490 void set_CTRS(CardTableRS* rs) { _rs = rs; }
491 };