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_MEMORY_CARDTABLEMODREFBS_HPP
26 #define SHARE_VM_MEMORY_CARDTABLEMODREFBS_HPP
27
28 #include "memory/modRefBarrierSet.hpp"
29 #include "oops/oop.hpp"
30 #include "oops/oop.inline2.hpp"
31
32 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
33 // enumerate ref fields that have been modified (since the last
34 // enumeration.)
35
36 // As it currently stands, this barrier is *imprecise*: when a ref field in
37 // an object "o" is modified, the card table entry for the card containing
38 // the head of "o" is dirtied, not necessarily the card containing the
39 // modified field itself. For object arrays, however, the barrier *is*
40 // precise; only the card containing the modified element is dirtied.
41 // Any MemRegionClosures used to scan dirty cards should take these
42 // considerations into account.
43
44 class Generation;
45 class OopsInGenClosure;
46 class DirtyCardToOopClosure;
47
48 class CardTableModRefBS: public ModRefBarrierSet {
49 // Some classes get to look at some private stuff.
50 friend class BytecodeInterpreter;
51 friend class VMStructs;
52 friend class CardTableRS;
53 friend class CheckForUnmarkedOops; // Needs access to raw card bytes.
54 friend class SharkBuilder;
55 #ifndef PRODUCT
56 // For debugging.
57 friend class GuaranteeNotModClosure;
58 #endif
59 protected:
60
61 enum CardValues {
62 clean_card = -1,
63 // The mask contains zeros in places for all other values.
64 clean_card_mask = clean_card - 31,
65
66 dirty_card = 0,
67 precleaned_card = 1,
68 claimed_card = 2,
69 deferred_card = 4,
70 last_card = 8,
71 CT_MR_BS_last_reserved = 16
72 };
73
74 // dirty and precleaned are equivalent wrt younger_refs_iter.
75 static bool card_is_dirty_wrt_gen_iter(jbyte cv) {
76 return cv == dirty_card || cv == precleaned_card;
77 }
78
79 // Returns "true" iff the value "cv" will cause the card containing it
80 // to be scanned in the current traversal. May be overridden by
81 // subtypes.
82 virtual bool card_will_be_scanned(jbyte cv) {
83 return CardTableModRefBS::card_is_dirty_wrt_gen_iter(cv);
84 }
85
86 // Returns "true" iff the value "cv" may have represented a dirty card at
87 // some point.
88 virtual bool card_may_have_been_dirty(jbyte cv) {
89 return card_is_dirty_wrt_gen_iter(cv);
90 }
91
92 // The declaration order of these const fields is important; see the
93 // constructor before changing.
94 const MemRegion _whole_heap; // the region covered by the card table
95 const size_t _guard_index; // index of very last element in the card
96 // table; it is set to a guard value
97 // (last_card) and should never be modified
98 const size_t _last_valid_index; // index of the last valid element
99 const size_t _page_size; // page size used when mapping _byte_map
100 const size_t _byte_map_size; // in bytes
101 jbyte* _byte_map; // the card marking array
102
103 int _cur_covered_regions;
104 // The covered regions should be in address order.
105 MemRegion* _covered;
106 // The committed regions correspond one-to-one to the covered regions.
107 // They represent the card-table memory that has been committed to service
108 // the corresponding covered region. It may be that committed region for
109 // one covered region corresponds to a larger region because of page-size
110 // roundings. Thus, a committed region for one covered region may
111 // actually extend onto the card-table space for the next covered region.
112 MemRegion* _committed;
113
114 // The last card is a guard card, and we commit the page for it so
115 // we can use the card for verification purposes. We make sure we never
116 // uncommit the MemRegion for that page.
117 MemRegion _guard_region;
118
119 protected:
120 // Initialization utilities; covered_words is the size of the covered region
121 // in, um, words.
122 inline size_t cards_required(size_t covered_words);
123 inline size_t compute_byte_map_size();
124
125 // Finds and return the index of the region, if any, to which the given
126 // region would be contiguous. If none exists, assign a new region and
127 // returns its index. Requires that no more than the maximum number of
128 // covered regions defined in the constructor are ever in use.
129 int find_covering_region_by_base(HeapWord* base);
130
131 // Same as above, but finds the region containing the given address
132 // instead of starting at a given base address.
133 int find_covering_region_containing(HeapWord* addr);
134
135 // Resize one of the regions covered by the remembered set.
136 void resize_covered_region(MemRegion new_region);
137
138 // Returns the leftmost end of a committed region corresponding to a
139 // covered region before covered region "ind", or else "NULL" if "ind" is
140 // the first covered region.
141 HeapWord* largest_prev_committed_end(int ind) const;
142
143 // Returns the part of the region mr that doesn't intersect with
144 // any committed region other than self. Used to prevent uncommitting
145 // regions that are also committed by other regions. Also protects
146 // against uncommitting the guard region.
147 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
148
149 // Mapping from address to card marking array entry
150 jbyte* byte_for(const void* p) const {
151 assert(_whole_heap.contains(p),
152 "out of bounds access to card marking array");
153 jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
154 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
155 "out of bounds accessor for card marking array");
156 return result;
157 }
158
159 // The card table byte one after the card marking array
160 // entry for argument address. Typically used for higher bounds
161 // for loops iterating through the card table.
162 jbyte* byte_after(const void* p) const {
163 return byte_for(p) + 1;
164 }
165
166 // Iterate over the portion of the card-table which covers the given
167 // region mr in the given space and apply cl to any dirty sub-regions
168 // of mr. cl and dcto_cl must either be the same closure or cl must
169 // wrap dcto_cl. Both are required - neither may be NULL. Also, dcto_cl
170 // may be modified. Note that this function will operate in a parallel
171 // mode if worker threads are available.
172 void non_clean_card_iterate(Space* sp, MemRegion mr,
173 DirtyCardToOopClosure* dcto_cl,
174 MemRegionClosure* cl,
175 bool clear);
176
177 // Utility function used to implement the other versions below.
178 void non_clean_card_iterate_work(MemRegion mr, MemRegionClosure* cl,
179 bool clear);
180
181 void par_non_clean_card_iterate_work(Space* sp, MemRegion mr,
182 DirtyCardToOopClosure* dcto_cl,
183 MemRegionClosure* cl,
184 bool clear,
185 int n_threads);
186
187 // Dirty the bytes corresponding to "mr" (not all of which must be
188 // covered.)
189 void dirty_MemRegion(MemRegion mr);
190
191 // Clear (to clean_card) the bytes entirely contained within "mr" (not
192 // all of which must be covered.)
193 void clear_MemRegion(MemRegion mr);
194
195 // *** Support for parallel card scanning.
196
197 enum SomeConstantsForParallelism {
198 StridesPerThread = 2,
199 CardsPerStrideChunk = 256
200 };
201
202 // This is an array, one element per covered region of the card table.
203 // Each entry is itself an array, with one element per chunk in the
204 // covered region. Each entry of these arrays is the lowest non-clean
205 // card of the corresponding chunk containing part of an object from the
206 // previous chunk, or else NULL.
207 typedef jbyte* CardPtr;
208 typedef CardPtr* CardArr;
209 CardArr* _lowest_non_clean;
210 size_t* _lowest_non_clean_chunk_size;
211 uintptr_t* _lowest_non_clean_base_chunk_index;
212 int* _last_LNC_resizing_collection;
213
214 // Initializes "lowest_non_clean" to point to the array for the region
215 // covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk
216 // index of the corresponding to the first element of that array.
217 // Ensures that these arrays are of sufficient size, allocating if necessary.
218 // May be called by several threads concurrently.
219 void get_LNC_array_for_space(Space* sp,
220 jbyte**& lowest_non_clean,
221 uintptr_t& lowest_non_clean_base_chunk_index,
222 size_t& lowest_non_clean_chunk_size);
223
224 // Returns the number of chunks necessary to cover "mr".
225 size_t chunks_to_cover(MemRegion mr) {
226 return (size_t)(addr_to_chunk_index(mr.last()) -
227 addr_to_chunk_index(mr.start()) + 1);
228 }
229
230 // Returns the index of the chunk in a stride which
231 // covers the given address.
232 uintptr_t addr_to_chunk_index(const void* addr) {
233 uintptr_t card = (uintptr_t) byte_for(addr);
234 return card / CardsPerStrideChunk;
235 }
236
237 // Apply cl, which must either itself apply dcto_cl or be dcto_cl,
238 // to the cards in the stride (of n_strides) within the given space.
239 void process_stride(Space* sp,
240 MemRegion used,
241 jint stride, int n_strides,
242 DirtyCardToOopClosure* dcto_cl,
243 MemRegionClosure* cl,
244 bool clear,
245 jbyte** lowest_non_clean,
246 uintptr_t lowest_non_clean_base_chunk_index,
247 size_t lowest_non_clean_chunk_size);
248
249 // Makes sure that chunk boundaries are handled appropriately, by
250 // adjusting the min_done of dcto_cl, and by using a special card-table
251 // value to indicate how min_done should be set.
252 void process_chunk_boundaries(Space* sp,
253 DirtyCardToOopClosure* dcto_cl,
254 MemRegion chunk_mr,
255 MemRegion used,
256 jbyte** lowest_non_clean,
257 uintptr_t lowest_non_clean_base_chunk_index,
258 size_t lowest_non_clean_chunk_size);
259
260 public:
261 // Constants
262 enum SomePublicConstants {
263 card_shift = 9,
264 card_size = 1 << card_shift,
265 card_size_in_words = card_size / sizeof(HeapWord)
266 };
267
268 static int clean_card_val() { return clean_card; }
269 static int clean_card_mask_val() { return clean_card_mask; }
270 static int dirty_card_val() { return dirty_card; }
271 static int claimed_card_val() { return claimed_card; }
272 static int precleaned_card_val() { return precleaned_card; }
273 static int deferred_card_val() { return deferred_card; }
274
275 // For RTTI simulation.
276 bool is_a(BarrierSet::Name bsn) {
277 return bsn == BarrierSet::CardTableModRef || ModRefBarrierSet::is_a(bsn);
278 }
279
280 CardTableModRefBS(MemRegion whole_heap, int max_covered_regions);
281
282 // *** Barrier set functions.
283
284 bool has_write_ref_pre_barrier() { return false; }
285
286 inline bool write_ref_needs_barrier(void* field, oop new_val) {
287 // Note that this assumes the perm gen is the highest generation
288 // in the address space
289 return new_val != NULL && !new_val->is_perm();
290 }
291
292 // Record a reference update. Note that these versions are precise!
293 // The scanning code has to handle the fact that the write barrier may be
294 // either precise or imprecise. We make non-virtual inline variants of
295 // these functions here for performance.
296 protected:
297 void write_ref_field_work(oop obj, size_t offset, oop newVal);
298 virtual void write_ref_field_work(void* field, oop newVal);
299 public:
300
301 bool has_write_ref_array_opt() { return true; }
302 bool has_write_region_opt() { return true; }
303
304 inline void inline_write_region(MemRegion mr) {
305 dirty_MemRegion(mr);
306 }
307 protected:
308 void write_region_work(MemRegion mr) {
309 inline_write_region(mr);
310 }
311 public:
312
313 inline void inline_write_ref_array(MemRegion mr) {
314 dirty_MemRegion(mr);
315 }
316 protected:
317 void write_ref_array_work(MemRegion mr) {
318 inline_write_ref_array(mr);
319 }
320 public:
321
322 bool is_aligned(HeapWord* addr) {
323 return is_card_aligned(addr);
324 }
325
326 // *** Card-table-barrier-specific things.
327
328 template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}
329
330 template <class T> inline void inline_write_ref_field(T* field, oop newVal) {
331 jbyte* byte = byte_for((void*)field);
332 *byte = dirty_card;
333 }
334
335 // These are used by G1, when it uses the card table as a temporary data
336 // structure for card claiming.
337 bool is_card_dirty(size_t card_index) {
338 return _byte_map[card_index] == dirty_card_val();
339 }
340
341 void mark_card_dirty(size_t card_index) {
342 _byte_map[card_index] = dirty_card_val();
343 }
344
345 bool is_card_claimed(size_t card_index) {
346 jbyte val = _byte_map[card_index];
347 return (val & (clean_card_mask_val() | claimed_card_val())) == claimed_card_val();
348 }
349
350 void set_card_claimed(size_t card_index) {
351 jbyte val = _byte_map[card_index];
352 if (val == clean_card_val()) {
353 val = (jbyte)claimed_card_val();
354 } else {
355 val |= (jbyte)claimed_card_val();
356 }
357 _byte_map[card_index] = val;
358 }
359
360 bool claim_card(size_t card_index);
361
362 bool is_card_clean(size_t card_index) {
363 return _byte_map[card_index] == clean_card_val();
364 }
365
366 bool is_card_deferred(size_t card_index) {
367 jbyte val = _byte_map[card_index];
368 return (val & (clean_card_mask_val() | deferred_card_val())) == deferred_card_val();
369 }
370
371 bool mark_card_deferred(size_t card_index);
372
373 // Card marking array base (adjusted for heap low boundary)
374 // This would be the 0th element of _byte_map, if the heap started at 0x0.
375 // But since the heap starts at some higher address, this points to somewhere
376 // before the beginning of the actual _byte_map.
377 jbyte* byte_map_base;
378
379 // Return true if "p" is at the start of a card.
380 bool is_card_aligned(HeapWord* p) {
381 jbyte* pcard = byte_for(p);
382 return (addr_for(pcard) == p);
383 }
384
385 // The kinds of precision a CardTableModRefBS may offer.
386 enum PrecisionStyle {
387 Precise,
388 ObjHeadPreciseArray
389 };
390
391 // Tells what style of precision this card table offers.
392 PrecisionStyle precision() {
393 return ObjHeadPreciseArray; // Only one supported for now.
394 }
395
396 // ModRefBS functions.
397 virtual void invalidate(MemRegion mr, bool whole_heap = false);
398 void clear(MemRegion mr);
399 void dirty(MemRegion mr);
400 void mod_oop_in_space_iterate(Space* sp, OopClosure* cl,
401 bool clear = false,
402 bool before_save_marks = false);
403
404 // *** Card-table-RemSet-specific things.
405
406 // Invoke "cl.do_MemRegion" on a set of MemRegions that collectively
407 // includes all the modified cards (expressing each card as a
408 // MemRegion). Thus, several modified cards may be lumped into one
409 // region. The regions are non-overlapping, and are visited in
410 // *decreasing* address order. (This order aids with imprecise card
411 // marking, where a dirty card may cause scanning, and summarization
412 // marking, of objects that extend onto subsequent cards.)
413 // If "clear" is true, the card is (conceptually) marked unmodified before
414 // applying the closure.
415 void mod_card_iterate(MemRegionClosure* cl, bool clear = false) {
416 non_clean_card_iterate_work(_whole_heap, cl, clear);
417 }
418
419 // Like the "mod_cards_iterate" above, except only invokes the closure
420 // for cards within the MemRegion "mr" (which is required to be
421 // card-aligned and sized.)
422 void mod_card_iterate(MemRegion mr, MemRegionClosure* cl,
423 bool clear = false) {
424 non_clean_card_iterate_work(mr, cl, clear);
425 }
426
427 static uintx ct_max_alignment_constraint();
428
429 // Apply closure "cl" to the dirty cards containing some part of
430 // MemRegion "mr".
431 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
432
433 // Return the MemRegion corresponding to the first maximal run
434 // of dirty cards lying completely within MemRegion mr.
435 // If reset is "true", then sets those card table entries to the given
436 // value.
437 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
438 int reset_val);
439
440 // Set all the dirty cards in the given region to precleaned state.
441 void preclean_dirty_cards(MemRegion mr);
442
443 // Provide read-only access to the card table array.
444 const jbyte* byte_for_const(const void* p) const {
445 return byte_for(p);
446 }
447 const jbyte* byte_after_const(const void* p) const {
448 return byte_after(p);
449 }
450
451 // Mapping from card marking array entry to address of first word
452 HeapWord* addr_for(const jbyte* p) const {
453 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
454 "out of bounds access to card marking array");
455 size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
456 HeapWord* result = (HeapWord*) (delta << card_shift);
457 assert(_whole_heap.contains(result),
458 "out of bounds accessor from card marking array");
459 return result;
460 }
461
462 // Mapping from address to card marking array index.
463 size_t index_for(void* p) {
464 assert(_whole_heap.contains(p),
465 "out of bounds access to card marking array");
466 return byte_for(p) - _byte_map;
467 }
468
469 const jbyte* byte_for_index(const size_t card_index) const {
470 return _byte_map + card_index;
471 }
472
473 void verify();
474 void verify_guard();
475
476 void verify_clean_region(MemRegion mr) PRODUCT_RETURN;
477 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
478
479 static size_t par_chunk_heapword_alignment() {
480 return CardsPerStrideChunk * card_size_in_words;
481 }
482
483 };
484
485 class CardTableRS;
486
487 // A specialization for the CardTableRS gen rem set.
488 class CardTableModRefBSForCTRS: public CardTableModRefBS {
489 CardTableRS* _rs;
490 protected:
491 bool card_will_be_scanned(jbyte cv);
492 bool card_may_have_been_dirty(jbyte cv);
493 public:
494 CardTableModRefBSForCTRS(MemRegion whole_heap,
495 int max_covered_regions) :
496 CardTableModRefBS(whole_heap, max_covered_regions) {}
497
498 void set_CTRS(CardTableRS* rs) { _rs = rs; }
499 };
500
501 #endif // SHARE_VM_MEMORY_CARDTABLEMODREFBS_HPP