1 /*
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24
25 #ifndef SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP
26 #define SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP
27
28 #include "gc/shared/modRefBarrierSet.hpp"
29 #include "utilities/align.hpp"
30
31 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
32 // enumerate ref fields that have been modified (since the last
33 // enumeration.)
34
35 // As it currently stands, this barrier is *imprecise*: when a ref field in
36 // an object "o" is modified, the card table entry for the card containing
37 // the head of "o" is dirtied, not necessarily the card containing the
38 // modified field itself. For object arrays, however, the barrier *is*
39 // precise; only the card containing the modified element is dirtied.
40 // Closures used to scan dirty cards should take these
41 // considerations into account.
42
43 class CardTableModRefBS: public ModRefBarrierSet {
44 // Some classes get to look at some private stuff.
45 friend class VMStructs;
46 protected:
47
48 enum CardValues {
49 clean_card = -1,
50 // The mask contains zeros in places for all other values.
51 clean_card_mask = clean_card - 31,
52
53 dirty_card = 0,
54 precleaned_card = 1,
55 claimed_card = 2,
56 deferred_card = 4,
57 last_card = 8,
58 CT_MR_BS_last_reserved = 16
59 };
60
61 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2
62 // or INCLUDE_JVMCI is being used
63 bool _defer_initial_card_mark;
64
65 // a word's worth (row) of clean card values
66 static const intptr_t clean_card_row = (intptr_t)(-1);
67
68 // The declaration order of these const fields is important; see the
69 // constructor before changing.
70 const MemRegion _whole_heap; // the region covered by the card table
71 size_t _guard_index; // index of very last element in the card
72 // table; it is set to a guard value
73 // (last_card) and should never be modified
74 size_t _last_valid_index; // index of the last valid element
75 const size_t _page_size; // page size used when mapping _byte_map
76 size_t _byte_map_size; // in bytes
77 jbyte* _byte_map; // the card marking array
78
79 // Some barrier sets create tables whose elements correspond to parts of
80 // the heap; the CardTableModRefBS is an example. Such barrier sets will
81 // normally reserve space for such tables, and commit parts of the table
82 // "covering" parts of the heap that are committed. At most one covered
83 // region per generation is needed.
84 static const int _max_covered_regions = 2;
85
86 int _cur_covered_regions;
87
88 // The covered regions should be in address order.
89 MemRegion* _covered;
90 // The committed regions correspond one-to-one to the covered regions.
91 // They represent the card-table memory that has been committed to service
92 // the corresponding covered region. It may be that committed region for
93 // one covered region corresponds to a larger region because of page-size
94 // roundings. Thus, a committed region for one covered region may
95 // actually extend onto the card-table space for the next covered region.
96 MemRegion* _committed;
97
98 // The last card is a guard card, and we commit the page for it so
99 // we can use the card for verification purposes. We make sure we never
100 // uncommit the MemRegion for that page.
101 MemRegion _guard_region;
102
103 inline size_t compute_byte_map_size();
104
105 // Finds and return the index of the region, if any, to which the given
106 // region would be contiguous. If none exists, assign a new region and
107 // returns its index. Requires that no more than the maximum number of
108 // covered regions defined in the constructor are ever in use.
109 int find_covering_region_by_base(HeapWord* base);
110
111 // Same as above, but finds the region containing the given address
112 // instead of starting at a given base address.
113 int find_covering_region_containing(HeapWord* addr);
114
115 // Resize one of the regions covered by the remembered set.
116 virtual void resize_covered_region(MemRegion new_region);
117
118 // Returns the leftmost end of a committed region corresponding to a
119 // covered region before covered region "ind", or else "NULL" if "ind" is
120 // the first covered region.
121 HeapWord* largest_prev_committed_end(int ind) const;
122
123 // Returns the part of the region mr that doesn't intersect with
124 // any committed region other than self. Used to prevent uncommitting
125 // regions that are also committed by other regions. Also protects
126 // against uncommitting the guard region.
127 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
128
129 // Mapping from address to card marking array entry
130 jbyte* byte_for(const void* p) const {
131 assert(_whole_heap.contains(p),
132 "Attempt to access p = " PTR_FORMAT " out of bounds of "
133 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
134 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
135 jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
136 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
137 "out of bounds accessor for card marking array");
138 return result;
139 }
140
141 // The card table byte one after the card marking array
142 // entry for argument address. Typically used for higher bounds
143 // for loops iterating through the card table.
144 jbyte* byte_after(const void* p) const {
145 return byte_for(p) + 1;
146 }
147
148 // Dirty the bytes corresponding to "mr" (not all of which must be
149 // covered.)
150 void dirty_MemRegion(MemRegion mr);
151
152 // Clear (to clean_card) the bytes entirely contained within "mr" (not
153 // all of which must be covered.)
154 void clear_MemRegion(MemRegion mr);
155
156 public:
157 // Constants
158 enum SomePublicConstants {
159 card_shift = 9,
160 card_size = 1 << card_shift,
161 card_size_in_words = card_size / sizeof(HeapWord)
162 };
163
164 static int clean_card_val() { return clean_card; }
165 static int clean_card_mask_val() { return clean_card_mask; }
166 static int dirty_card_val() { return dirty_card; }
167 static int claimed_card_val() { return claimed_card; }
168 static int precleaned_card_val() { return precleaned_card; }
169 static int deferred_card_val() { return deferred_card; }
170
171 virtual void initialize();
172
173 // *** Barrier set functions.
174
175 // Initialization utilities; covered_words is the size of the covered region
176 // in, um, words.
177 inline size_t cards_required(size_t covered_words) {
178 // Add one for a guard card, used to detect errors.
179 const size_t words = align_up(covered_words, card_size_in_words);
180 return words / card_size_in_words + 1;
181 }
182
183 protected:
184 CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);
185 ~CardTableModRefBS();
186
187 public:
188 void write_region(MemRegion mr) {
189 dirty_MemRegion(mr);
190 }
191
192 protected:
193 void write_ref_array_work(MemRegion mr) {
194 dirty_MemRegion(mr);
195 }
196
197 public:
198 bool is_aligned(HeapWord* addr) {
199 return is_card_aligned(addr);
200 }
201
202 // *** Card-table-barrier-specific things.
203
204 // Record a reference update. Note that these versions are precise!
205 // The scanning code has to handle the fact that the write barrier may be
206 // either precise or imprecise. We make non-virtual inline variants of
207 // these functions here for performance.
208 template <DecoratorSet decorators, typename T>
209 void write_ref_field_post(T* field, oop newVal);
210
211 // These are used by G1, when it uses the card table as a temporary data
212 // structure for card claiming.
213 bool is_card_dirty(size_t card_index) {
214 return _byte_map[card_index] == dirty_card_val();
215 }
216
217 void mark_card_dirty(size_t card_index) {
218 _byte_map[card_index] = dirty_card_val();
219 }
220
221 bool is_card_clean(size_t card_index) {
222 return _byte_map[card_index] == clean_card_val();
223 }
224
225 // Card marking array base (adjusted for heap low boundary)
226 // This would be the 0th element of _byte_map, if the heap started at 0x0.
227 // But since the heap starts at some higher address, this points to somewhere
228 // before the beginning of the actual _byte_map.
229 jbyte* byte_map_base;
230
231 // Return true if "p" is at the start of a card.
232 bool is_card_aligned(HeapWord* p) {
233 jbyte* pcard = byte_for(p);
234 return (addr_for(pcard) == p);
235 }
236
237 HeapWord* align_to_card_boundary(HeapWord* p) {
238 jbyte* pcard = byte_for(p + card_size_in_words - 1);
239 return addr_for(pcard);
240 }
241
242 // The kinds of precision a CardTableModRefBS may offer.
243 enum PrecisionStyle {
244 Precise,
245 ObjHeadPreciseArray
246 };
247
248 // Tells what style of precision this card table offers.
249 PrecisionStyle precision() {
250 return ObjHeadPreciseArray; // Only one supported for now.
251 }
252
253 // ModRefBS functions.
254 virtual void invalidate(MemRegion mr);
255 void clear(MemRegion mr);
256 void dirty(MemRegion mr);
257
258 // *** Card-table-RemSet-specific things.
259
260 static uintx ct_max_alignment_constraint();
261
262 // Apply closure "cl" to the dirty cards containing some part of
263 // MemRegion "mr".
264 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
265
266 // Return the MemRegion corresponding to the first maximal run
267 // of dirty cards lying completely within MemRegion mr.
268 // If reset is "true", then sets those card table entries to the given
269 // value.
270 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
271 int reset_val);
272
273 // Provide read-only access to the card table array.
274 const jbyte* byte_for_const(const void* p) const {
275 return byte_for(p);
276 }
277 const jbyte* byte_after_const(const void* p) const {
278 return byte_after(p);
279 }
280
281 // Mapping from card marking array entry to address of first word
282 HeapWord* addr_for(const jbyte* p) const {
283 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
284 "out of bounds access to card marking array. p: " PTR_FORMAT
285 " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
286 p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
287 size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
288 HeapWord* result = (HeapWord*) (delta << card_shift);
289 assert(_whole_heap.contains(result),
290 "Returning result = " PTR_FORMAT " out of bounds of "
291 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
292 p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
293 return result;
294 }
295
296 // Mapping from address to card marking array index.
297 size_t index_for(void* p) {
298 assert(_whole_heap.contains(p),
299 "Attempt to access p = " PTR_FORMAT " out of bounds of "
300 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
301 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
302 return byte_for(p) - _byte_map;
303 }
304
305 const jbyte* byte_for_index(const size_t card_index) const {
306 return _byte_map + card_index;
307 }
308
309 // Print a description of the memory for the barrier set
310 virtual void print_on(outputStream* st) const;
311
312 void verify();
313 void verify_guard();
314
315 // val_equals -> it will check that all cards covered by mr equal val
316 // !val_equals -> it will check that all cards covered by mr do not equal val
317 void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;
318 void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
319 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
320
321 // ReduceInitialCardMarks
322 void initialize_deferred_card_mark_barriers();
323
324 // If the CollectedHeap was asked to defer a store barrier above,
325 // this informs it to flush such a deferred store barrier to the
326 // remembered set.
327 void flush_deferred_card_mark_barrier(JavaThread* thread);
328
329 // Can a compiler initialize a new object without store barriers?
330 // This permission only extends from the creation of a new object
331 // via a TLAB up to the first subsequent safepoint. If such permission
332 // is granted for this heap type, the compiler promises to call
333 // defer_store_barrier() below on any slow path allocation of
334 // a new object for which such initializing store barriers will
335 // have been elided. G1, like CMS, allows this, but should be
336 // ready to provide a compensating write barrier as necessary
337 // if that storage came out of a non-young region. The efficiency
338 // of this implementation depends crucially on being able to
339 // answer very efficiently in constant time whether a piece of
340 // storage in the heap comes from a young region or not.
341 // See ReduceInitialCardMarks.
342 virtual bool can_elide_tlab_store_barriers() const {
343 return true;
344 }
345
346 // If a compiler is eliding store barriers for TLAB-allocated objects,
347 // we will be informed of a slow-path allocation by a call
348 // to on_slowpath_allocation_exit() below. Such a call precedes the
349 // initialization of the object itself, and no post-store-barriers will
350 // be issued. Some heap types require that the barrier strictly follows
351 // the initializing stores. (This is currently implemented by deferring the
352 // barrier until the next slow-path allocation or gc-related safepoint.)
353 // This interface answers whether a particular barrier type needs the card
354 // mark to be thus strictly sequenced after the stores.
355 virtual bool card_mark_must_follow_store() const = 0;
356
357 virtual bool is_in_young(oop obj) const = 0;
358
359 virtual void on_slowpath_allocation_exit(JavaThread* thread, oop new_obj);
360 virtual void flush_deferred_barriers(JavaThread* thread);
361
362 virtual void make_parsable(JavaThread* thread) { flush_deferred_card_mark_barrier(thread); }
363
364 template <DecoratorSet decorators, typename BarrierSetT = CardTableModRefBS>
365 class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {};
366 };
367
368 template<>
369 struct BarrierSet::GetName<CardTableModRefBS> {
370 static const BarrierSet::Name value = BarrierSet::CardTableModRef;
371 };
372
373 template<>
374 struct BarrierSet::GetType<BarrierSet::CardTableModRef> {
375 typedef CardTableModRefBS type;
376 };
377
378 #endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP