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_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 // a word's worth (row) of clean card values
62 static const intptr_t clean_card_row = (intptr_t)(-1);
63
64 // The declaration order of these const fields is important; see the
65 // constructor before changing.
66 const MemRegion _whole_heap; // the region covered by the card table
67 size_t _guard_index; // index of very last element in the card
68 // table; it is set to a guard value
69 // (last_card) and should never be modified
70 size_t _last_valid_index; // index of the last valid element
71 const size_t _page_size; // page size used when mapping _byte_map
72 size_t _byte_map_size; // in bytes
73 jbyte* _byte_map; // the card marking array
74
75 // Some barrier sets create tables whose elements correspond to parts of
76 // the heap; the CardTableModRefBS is an example. Such barrier sets will
77 // normally reserve space for such tables, and commit parts of the table
78 // "covering" parts of the heap that are committed. At most one covered
79 // region per generation is needed.
80 static const int _max_covered_regions = 2;
81
82 int _cur_covered_regions;
83
84 // The covered regions should be in address order.
85 MemRegion* _covered;
86 // The committed regions correspond one-to-one to the covered regions.
87 // They represent the card-table memory that has been committed to service
88 // the corresponding covered region. It may be that committed region for
89 // one covered region corresponds to a larger region because of page-size
90 // roundings. Thus, a committed region for one covered region may
91 // actually extend onto the card-table space for the next covered region.
92 MemRegion* _committed;
93
94 // The last card is a guard card, and we commit the page for it so
95 // we can use the card for verification purposes. We make sure we never
96 // uncommit the MemRegion for that page.
97 MemRegion _guard_region;
98
99 inline size_t compute_byte_map_size();
100
101 // Finds and return the index of the region, if any, to which the given
102 // region would be contiguous. If none exists, assign a new region and
103 // returns its index. Requires that no more than the maximum number of
104 // covered regions defined in the constructor are ever in use.
105 int find_covering_region_by_base(HeapWord* base);
106
107 // Same as above, but finds the region containing the given address
108 // instead of starting at a given base address.
109 int find_covering_region_containing(HeapWord* addr);
110
111 // Resize one of the regions covered by the remembered set.
112 virtual void resize_covered_region(MemRegion new_region);
113
114 // Returns the leftmost end of a committed region corresponding to a
115 // covered region before covered region "ind", or else "NULL" if "ind" is
116 // the first covered region.
117 HeapWord* largest_prev_committed_end(int ind) const;
118
119 // Returns the part of the region mr that doesn't intersect with
120 // any committed region other than self. Used to prevent uncommitting
121 // regions that are also committed by other regions. Also protects
122 // against uncommitting the guard region.
123 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
124
125 // Mapping from address to card marking array entry
126 jbyte* byte_for(const void* p) const {
127 assert(_whole_heap.contains(p),
128 "Attempt to access p = " PTR_FORMAT " out of bounds of "
129 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
130 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
131 jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
132 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
133 "out of bounds accessor for card marking array");
134 return result;
135 }
136
137 // The card table byte one after the card marking array
138 // entry for argument address. Typically used for higher bounds
139 // for loops iterating through the card table.
140 jbyte* byte_after(const void* p) const {
141 return byte_for(p) + 1;
142 }
143
144 // Dirty the bytes corresponding to "mr" (not all of which must be
145 // covered.)
146 void dirty_MemRegion(MemRegion mr);
147
148 // Clear (to clean_card) the bytes entirely contained within "mr" (not
149 // all of which must be covered.)
150 void clear_MemRegion(MemRegion mr);
151
152 public:
153 // Constants
154 enum SomePublicConstants {
155 card_shift = 9,
156 card_size = 1 << card_shift,
157 card_size_in_words = card_size / sizeof(HeapWord)
158 };
159
160 static int clean_card_val() { return clean_card; }
161 static int clean_card_mask_val() { return clean_card_mask; }
162 static int dirty_card_val() { return dirty_card; }
163 static int claimed_card_val() { return claimed_card; }
164 static int precleaned_card_val() { return precleaned_card; }
165 static int deferred_card_val() { return deferred_card; }
166
167 virtual void initialize();
168
169 // *** Barrier set functions.
170
171 // Initialization utilities; covered_words is the size of the covered region
172 // in, um, words.
173 inline size_t cards_required(size_t covered_words) {
174 // Add one for a guard card, used to detect errors.
175 const size_t words = align_up(covered_words, card_size_in_words);
176 return words / card_size_in_words + 1;
177 }
178
179 protected:
180 CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);
181 ~CardTableModRefBS();
182
183 protected:
184 void write_region_work(MemRegion mr) {
185 dirty_MemRegion(mr);
186 }
187
188 protected:
189 void write_ref_array_work(MemRegion mr) {
190 dirty_MemRegion(mr);
191 }
192
193 public:
194 bool is_aligned(HeapWord* addr) {
195 return is_card_aligned(addr);
196 }
197
198 // *** Card-table-barrier-specific things.
199
200 // Record a reference update. Note that these versions are precise!
201 // The scanning code has to handle the fact that the write barrier may be
202 // either precise or imprecise. We make non-virtual inline variants of
203 // these functions here for performance.
204 template <DecoratorSet decorators, typename T>
205 void write_ref_field_post(T* field, oop newVal);
206
207 // These are used by G1, when it uses the card table as a temporary data
208 // structure for card claiming.
209 bool is_card_dirty(size_t card_index) {
210 return _byte_map[card_index] == dirty_card_val();
211 }
212
213 void mark_card_dirty(size_t card_index) {
214 _byte_map[card_index] = dirty_card_val();
215 }
216
217 bool is_card_clean(size_t card_index) {
218 return _byte_map[card_index] == clean_card_val();
219 }
220
221 // Card marking array base (adjusted for heap low boundary)
222 // This would be the 0th element of _byte_map, if the heap started at 0x0.
223 // But since the heap starts at some higher address, this points to somewhere
224 // before the beginning of the actual _byte_map.
225 jbyte* byte_map_base;
226
227 // Return true if "p" is at the start of a card.
228 bool is_card_aligned(HeapWord* p) {
229 jbyte* pcard = byte_for(p);
230 return (addr_for(pcard) == p);
231 }
232
233 HeapWord* align_to_card_boundary(HeapWord* p) {
234 jbyte* pcard = byte_for(p + card_size_in_words - 1);
235 return addr_for(pcard);
236 }
237
238 // The kinds of precision a CardTableModRefBS may offer.
239 enum PrecisionStyle {
240 Precise,
241 ObjHeadPreciseArray
242 };
243
244 // Tells what style of precision this card table offers.
245 PrecisionStyle precision() {
246 return ObjHeadPreciseArray; // Only one supported for now.
247 }
248
249 // ModRefBS functions.
250 virtual void invalidate(MemRegion mr);
251 void clear(MemRegion mr);
252 void dirty(MemRegion mr);
253
254 // *** Card-table-RemSet-specific things.
255
256 static uintx ct_max_alignment_constraint();
257
258 // Apply closure "cl" to the dirty cards containing some part of
259 // MemRegion "mr".
260 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
261
262 // Return the MemRegion corresponding to the first maximal run
263 // of dirty cards lying completely within MemRegion mr.
264 // If reset is "true", then sets those card table entries to the given
265 // value.
266 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
267 int reset_val);
268
269 // Provide read-only access to the card table array.
270 const jbyte* byte_for_const(const void* p) const {
271 return byte_for(p);
272 }
273 const jbyte* byte_after_const(const void* p) const {
274 return byte_after(p);
275 }
276
277 // Mapping from card marking array entry to address of first word
278 HeapWord* addr_for(const jbyte* p) const {
279 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
280 "out of bounds access to card marking array. p: " PTR_FORMAT
281 " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
282 p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
283 size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
284 HeapWord* result = (HeapWord*) (delta << card_shift);
285 assert(_whole_heap.contains(result),
286 "Returning result = " PTR_FORMAT " out of bounds of "
287 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
288 p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
289 return result;
290 }
291
292 // Mapping from address to card marking array index.
293 size_t index_for(void* p) {
294 assert(_whole_heap.contains(p),
295 "Attempt to access p = " PTR_FORMAT " out of bounds of "
296 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
297 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
298 return byte_for(p) - _byte_map;
299 }
300
301 const jbyte* byte_for_index(const size_t card_index) const {
302 return _byte_map + card_index;
303 }
304
305 // Print a description of the memory for the barrier set
306 virtual void print_on(outputStream* st) const;
307
308 void verify();
309 void verify_guard();
310
311 // val_equals -> it will check that all cards covered by mr equal val
312 // !val_equals -> it will check that all cards covered by mr do not equal val
313 void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;
314 void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
315 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
316
317 template <DecoratorSet decorators, typename BarrierSetT = CardTableModRefBS>
318 class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {};
319 };
320
321 template<>
322 struct BarrierSet::GetName<CardTableModRefBS> {
323 static const BarrierSet::Name value = BarrierSet::CardTableModRef;
324 };
325
326 template<>
327 struct BarrierSet::GetType<BarrierSet::CardTableModRef> {
328 typedef CardTableModRefBS type;
329 };
330
331 #endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP