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 "oops/oop.hpp"
30 #include "utilities/align.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 // Closures used to scan dirty cards should take these
42 // considerations into account.
43
44 class CardTableModRefBS: public ModRefBarrierSet {
45 // Some classes get to look at some private stuff.
46 friend class VMStructs;
47 protected:
48
49 enum CardValues {
50 clean_card = -1,
51 // The mask contains zeros in places for all other values.
52 clean_card_mask = clean_card - 31,
53
54 dirty_card = 0,
55 precleaned_card = 1,
56 claimed_card = 2,
57 deferred_card = 4,
58 last_card = 8,
59 CT_MR_BS_last_reserved = 16
60 };
61
62 // a word's worth (row) of clean card values
63 static const intptr_t clean_card_row = (intptr_t)(-1);
64
65 // The declaration order of these const fields is important; see the
66 // constructor before changing.
67 const MemRegion _whole_heap; // the region covered by the card table
68 size_t _guard_index; // index of very last element in the card
69 // table; it is set to a guard value
70 // (last_card) and should never be modified
71 size_t _last_valid_index; // index of the last valid element
72 const size_t _page_size; // page size used when mapping _byte_map
73 size_t _byte_map_size; // in bytes
74 jbyte* _byte_map; // the card marking array
75
76 int _cur_covered_regions;
77 // The covered regions should be in address order.
78 MemRegion* _covered;
79 // The committed regions correspond one-to-one to the covered regions.
80 // They represent the card-table memory that has been committed to service
81 // the corresponding covered region. It may be that committed region for
82 // one covered region corresponds to a larger region because of page-size
83 // roundings. Thus, a committed region for one covered region may
84 // actually extend onto the card-table space for the next covered region.
85 MemRegion* _committed;
86
87 // The last card is a guard card, and we commit the page for it so
88 // we can use the card for verification purposes. We make sure we never
89 // uncommit the MemRegion for that page.
90 MemRegion _guard_region;
91
92 protected:
93 inline size_t compute_byte_map_size();
94
95 // Finds and return the index of the region, if any, to which the given
96 // region would be contiguous. If none exists, assign a new region and
97 // returns its index. Requires that no more than the maximum number of
98 // covered regions defined in the constructor are ever in use.
99 int find_covering_region_by_base(HeapWord* base);
100
101 // Same as above, but finds the region containing the given address
102 // instead of starting at a given base address.
103 int find_covering_region_containing(HeapWord* addr);
104
105 // Resize one of the regions covered by the remembered set.
106 virtual void resize_covered_region(MemRegion new_region);
107
108 // Returns the leftmost end of a committed region corresponding to a
109 // covered region before covered region "ind", or else "NULL" if "ind" is
110 // the first covered region.
111 HeapWord* largest_prev_committed_end(int ind) const;
112
113 // Returns the part of the region mr that doesn't intersect with
114 // any committed region other than self. Used to prevent uncommitting
115 // regions that are also committed by other regions. Also protects
116 // against uncommitting the guard region.
117 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
118
119 // Mapping from address to card marking array entry
120 jbyte* byte_for(const void* p) const {
121 assert(_whole_heap.contains(p),
122 "Attempt to access p = " PTR_FORMAT " out of bounds of "
123 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
124 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
125 jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
126 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
127 "out of bounds accessor for card marking array");
128 return result;
129 }
130
131 // The card table byte one after the card marking array
132 // entry for argument address. Typically used for higher bounds
133 // for loops iterating through the card table.
134 jbyte* byte_after(const void* p) const {
135 return byte_for(p) + 1;
136 }
137
138 protected:
139 // Dirty the bytes corresponding to "mr" (not all of which must be
140 // covered.)
141 void dirty_MemRegion(MemRegion mr);
142
143 // Clear (to clean_card) the bytes entirely contained within "mr" (not
144 // all of which must be covered.)
145 void clear_MemRegion(MemRegion mr);
146
147 public:
148 // Constants
149 enum SomePublicConstants {
150 card_shift = 9,
151 card_size = 1 << card_shift,
152 card_size_in_words = card_size / sizeof(HeapWord)
153 };
154
155 static int clean_card_val() { return clean_card; }
156 static int clean_card_mask_val() { return clean_card_mask; }
157 static int dirty_card_val() { return dirty_card; }
158 static int claimed_card_val() { return claimed_card; }
159 static int precleaned_card_val() { return precleaned_card; }
160 static int deferred_card_val() { return deferred_card; }
161
162 virtual void initialize();
163
164 // *** Barrier set functions.
165
166 bool has_write_ref_pre_barrier() { return false; }
167
168 // Initialization utilities; covered_words is the size of the covered region
169 // in, um, words.
170 inline size_t cards_required(size_t covered_words) {
171 // Add one for a guard card, used to detect errors.
172 const size_t words = align_up(covered_words, card_size_in_words);
173 return words / card_size_in_words + 1;
174 }
175
176 protected:
177
178 CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);
179 ~CardTableModRefBS();
180
181 // Record a reference update. Note that these versions are precise!
182 // The scanning code has to handle the fact that the write barrier may be
183 // either precise or imprecise. We make non-virtual inline variants of
184 // these functions here for performance.
185
186 void write_ref_field_work(oop obj, size_t offset, oop newVal);
187 virtual void write_ref_field_work(void* field, oop newVal, bool release);
188 public:
189
190 bool has_write_ref_array_opt() { return true; }
191 bool has_write_region_opt() { return true; }
192
193 inline void inline_write_region(MemRegion mr) {
194 dirty_MemRegion(mr);
195 }
196 protected:
197 void write_region_work(MemRegion mr) {
198 inline_write_region(mr);
199 }
200 public:
201
202 inline void inline_write_ref_array(MemRegion mr) {
203 dirty_MemRegion(mr);
204 }
205 protected:
206 void write_ref_array_work(MemRegion mr) {
207 inline_write_ref_array(mr);
208 }
209 public:
210
211 bool is_aligned(HeapWord* addr) {
212 return is_card_aligned(addr);
213 }
214
215 // *** Card-table-barrier-specific things.
216
217 template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}
218
219 template <class T> inline void inline_write_ref_field(T* field, oop newVal, bool release);
220
221 // These are used by G1, when it uses the card table as a temporary data
222 // structure for card claiming.
223 bool is_card_dirty(size_t card_index) {
224 return _byte_map[card_index] == dirty_card_val();
225 }
226
227 void mark_card_dirty(size_t card_index) {
228 _byte_map[card_index] = dirty_card_val();
229 }
230
231 bool is_card_clean(size_t card_index) {
232 return _byte_map[card_index] == clean_card_val();
233 }
234
235 // Card marking array base (adjusted for heap low boundary)
236 // This would be the 0th element of _byte_map, if the heap started at 0x0.
237 // But since the heap starts at some higher address, this points to somewhere
238 // before the beginning of the actual _byte_map.
239 jbyte* byte_map_base;
240
241 // Return true if "p" is at the start of a card.
242 bool is_card_aligned(HeapWord* p) {
243 jbyte* pcard = byte_for(p);
244 return (addr_for(pcard) == p);
245 }
246
247 HeapWord* align_to_card_boundary(HeapWord* p) {
248 jbyte* pcard = byte_for(p + card_size_in_words - 1);
249 return addr_for(pcard);
250 }
251
252 // The kinds of precision a CardTableModRefBS may offer.
253 enum PrecisionStyle {
254 Precise,
255 ObjHeadPreciseArray
256 };
257
258 // Tells what style of precision this card table offers.
259 PrecisionStyle precision() {
260 return ObjHeadPreciseArray; // Only one supported for now.
261 }
262
263 // ModRefBS functions.
264 virtual void invalidate(MemRegion mr);
265 void clear(MemRegion mr);
266 void dirty(MemRegion mr);
267
268 // *** Card-table-RemSet-specific things.
269
270 static uintx ct_max_alignment_constraint();
271
272 // Apply closure "cl" to the dirty cards containing some part of
273 // MemRegion "mr".
274 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
275
276 // Return the MemRegion corresponding to the first maximal run
277 // of dirty cards lying completely within MemRegion mr.
278 // If reset is "true", then sets those card table entries to the given
279 // value.
280 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
281 int reset_val);
282
283 // Provide read-only access to the card table array.
284 const jbyte* byte_for_const(const void* p) const {
285 return byte_for(p);
286 }
287 const jbyte* byte_after_const(const void* p) const {
288 return byte_after(p);
289 }
290
291 // Mapping from card marking array entry to address of first word
292 HeapWord* addr_for(const jbyte* p) const {
293 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
294 "out of bounds access to card marking array. p: " PTR_FORMAT
295 " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
296 p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
297 size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
298 HeapWord* result = (HeapWord*) (delta << card_shift);
299 assert(_whole_heap.contains(result),
300 "Returning result = " PTR_FORMAT " out of bounds of "
301 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
302 p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
303 return result;
304 }
305
306 // Mapping from address to card marking array index.
307 size_t index_for(void* p) {
308 assert(_whole_heap.contains(p),
309 "Attempt to access p = " PTR_FORMAT " out of bounds of "
310 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
311 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
312 return byte_for(p) - _byte_map;
313 }
314
315 const jbyte* byte_for_index(const size_t card_index) const {
316 return _byte_map + card_index;
317 }
318
319 // Print a description of the memory for the barrier set
320 virtual void print_on(outputStream* st) const;
321
322 void verify();
323 void verify_guard();
324
325 // val_equals -> it will check that all cards covered by mr equal val
326 // !val_equals -> it will check that all cards covered by mr do not equal val
327 void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;
328 void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
329 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
330 };
331
332 template<>
333 struct BarrierSet::GetName<CardTableModRefBS> {
334 static const BarrierSet::Name value = BarrierSet::CardTableModRef;
335 };
336
337
338 #endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP