1 /*
2 * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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).
14 *
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23 */
24
25 #ifndef SHARE_GC_SHARED_CARDTABLE_HPP
26 #define SHARE_GC_SHARED_CARDTABLE_HPP
27
28 #include "memory/allocation.hpp"
29 #include "memory/memRegion.hpp"
30 #include "oops/oopsHierarchy.hpp"
31 #include "utilities/align.hpp"
32
33 class CardTable: public CHeapObj<mtGC> {
34 friend class VMStructs;
35 public:
36 typedef uint8_t CardValue;
37
38 // All code generators assume that the size of a card table entry is one byte.
39 // They need to be updated to reflect any change to this.
40 // This code can typically be found by searching for the byte_map_base() method.
41 STATIC_ASSERT(sizeof(CardValue) == 1);
42
43 protected:
44 // The declaration order of these const fields is important; see the
45 // constructor before changing.
46 const bool _scanned_concurrently;
47 const MemRegion _whole_heap; // the region covered by the card table
48 size_t _guard_index; // index of very last element in the card
49 // table; it is set to a guard value
50 // (last_card) and should never be modified
51 size_t _last_valid_index; // index of the last valid element
52 const size_t _page_size; // page size used when mapping _byte_map
53 size_t _byte_map_size; // in bytes
54 CardValue* _byte_map; // the card marking array
55 CardValue* _byte_map_base;
56
57 int _cur_covered_regions;
58
59 // The covered regions should be in address order.
60 MemRegion* _covered;
61 // The committed regions correspond one-to-one to the covered regions.
62 // They represent the card-table memory that has been committed to service
63 // the corresponding covered region. It may be that committed region for
64 // one covered region corresponds to a larger region because of page-size
65 // roundings. Thus, a committed region for one covered region may
66 // actually extend onto the card-table space for the next covered region.
67 MemRegion* _committed;
68
69 // The last card is a guard card, and we commit the page for it so
70 // we can use the card for verification purposes. We make sure we never
71 // uncommit the MemRegion for that page.
72 MemRegion _guard_region;
73
74 inline size_t compute_byte_map_size();
75
76 // Finds and return the index of the region, if any, to which the given
77 // region would be contiguous. If none exists, assign a new region and
78 // returns its index. Requires that no more than the maximum number of
79 // covered regions defined in the constructor are ever in use.
80 int find_covering_region_by_base(HeapWord* base);
81
82 // Same as above, but finds the region containing the given address
83 // instead of starting at a given base address.
84 int find_covering_region_containing(HeapWord* addr);
85
86 // Returns the leftmost end of a committed region corresponding to a
87 // covered region before covered region "ind", or else "NULL" if "ind" is
88 // the first covered region.
89 HeapWord* largest_prev_committed_end(int ind) const;
90
91 // Returns the part of the region mr that doesn't intersect with
92 // any committed region other than self. Used to prevent uncommitting
93 // regions that are also committed by other regions. Also protects
94 // against uncommitting the guard region.
95 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
96
97 // Some barrier sets create tables whose elements correspond to parts of
98 // the heap; the CardTableBarrierSet is an example. Such barrier sets will
99 // normally reserve space for such tables, and commit parts of the table
100 // "covering" parts of the heap that are committed. At most one covered
101 // region per generation is needed.
102 static const int _max_covered_regions = 2;
103
104 enum CardValues {
105 clean_card = (CardValue)-1,
106
107 dirty_card = 0,
108 precleaned_card = 1,
109 last_card = 2,
110 CT_MR_BS_last_reserved = 4
111 };
112
113 // a word's worth (row) of clean card values
114 static const intptr_t clean_card_row = (intptr_t)(-1);
115
116 public:
117 CardTable(MemRegion whole_heap, bool conc_scan);
118 virtual ~CardTable();
119 virtual void initialize();
120
121 // The kinds of precision a CardTable may offer.
122 enum PrecisionStyle {
123 Precise,
124 ObjHeadPreciseArray
125 };
126
127 // Tells what style of precision this card table offers.
128 PrecisionStyle precision() {
129 return ObjHeadPreciseArray; // Only one supported for now.
130 }
131
132 // *** Barrier set functions.
133
134 // Initialization utilities; covered_words is the size of the covered region
135 // in, um, words.
136 inline size_t cards_required(size_t covered_words) {
137 // Add one for a guard card, used to detect errors.
138 const size_t words = align_up(covered_words, card_size_in_words);
139 return words / card_size_in_words + 1;
140 }
141
142 // Dirty the bytes corresponding to "mr" (not all of which must be
143 // covered.)
144 void dirty_MemRegion(MemRegion mr);
145
146 // Clear (to clean_card) the bytes entirely contained within "mr" (not
147 // all of which must be covered.)
148 void clear_MemRegion(MemRegion mr);
149
150 // Return true if "p" is at the start of a card.
151 bool is_card_aligned(HeapWord* p) {
152 CardValue* pcard = byte_for(p);
153 return (addr_for(pcard) == p);
154 }
155
156 // Mapping from address to card marking array entry
157 CardValue* byte_for(const void* p) const {
158 assert(_whole_heap.contains(p),
159 "Attempt to access p = " PTR_FORMAT " out of bounds of "
160 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
161 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
162 CardValue* result = &_byte_map_base[uintptr_t(p) >> card_shift];
163 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
164 "out of bounds accessor for card marking array");
165 return result;
166 }
167
168 // The card table byte one after the card marking array
169 // entry for argument address. Typically used for higher bounds
170 // for loops iterating through the card table.
171 CardValue* byte_after(const void* p) const {
172 return byte_for(p) + 1;
173 }
174
175 virtual void invalidate(MemRegion mr);
176 void clear(MemRegion mr);
177 void dirty(MemRegion mr);
178
179 // Provide read-only access to the card table array.
180 const CardValue* byte_for_const(const void* p) const {
181 return byte_for(p);
182 }
183 const CardValue* byte_after_const(const void* p) const {
184 return byte_after(p);
185 }
186
187 // Mapping from card marking array entry to address of first word
188 HeapWord* addr_for(const CardValue* p) const {
189 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
190 "out of bounds access to card marking array. p: " PTR_FORMAT
191 " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
192 p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
193 size_t delta = pointer_delta(p, _byte_map_base, sizeof(CardValue));
194 HeapWord* result = (HeapWord*) (delta << card_shift);
195 assert(_whole_heap.contains(result),
196 "Returning result = " PTR_FORMAT " out of bounds of "
197 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
198 p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
199 return result;
200 }
201
202 // Mapping from address to card marking array index.
203 size_t index_for(void* p) {
204 assert(_whole_heap.contains(p),
205 "Attempt to access p = " PTR_FORMAT " out of bounds of "
206 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
207 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
208 return byte_for(p) - _byte_map;
209 }
210
211 CardValue* byte_for_index(const size_t card_index) const {
212 return _byte_map + card_index;
213 }
214
215 // Resize one of the regions covered by the remembered set.
216 virtual void resize_covered_region(MemRegion new_region);
217
218 // *** Card-table-RemSet-specific things.
219
220 static uintx ct_max_alignment_constraint();
221
222 // Apply closure "cl" to the dirty cards containing some part of
223 // MemRegion "mr".
224 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
225
226 // Return the MemRegion corresponding to the first maximal run
227 // of dirty cards lying completely within MemRegion mr.
228 // If reset is "true", then sets those card table entries to the given
229 // value.
230 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
231 int reset_val);
232
233 // Constants
234 enum SomePublicConstants {
235 card_shift = 9,
236 card_size = 1 << card_shift,
237 card_size_in_words = card_size / sizeof(HeapWord)
238 };
239
240 static CardValue clean_card_val() { return clean_card; }
241 static CardValue dirty_card_val() { return dirty_card; }
242 static CardValue precleaned_card_val() { return precleaned_card; }
243 static intptr_t clean_card_row_val() { return clean_card_row; }
244
245 // Card marking array base (adjusted for heap low boundary)
246 // This would be the 0th element of _byte_map, if the heap started at 0x0.
247 // But since the heap starts at some higher address, this points to somewhere
248 // before the beginning of the actual _byte_map.
249 CardValue* byte_map_base() const { return _byte_map_base; }
250 bool scanned_concurrently() const { return _scanned_concurrently; }
251 size_t byte_map_top_offset() const { return uintptr_t(_whole_heap.end()); }
252 size_t byte_map_bottom_offset() const { return uintptr_t(_whole_heap.start()); }
253
254 virtual bool is_in_young(oop obj) const = 0;
255
256 // Print a description of the memory for the card table
257 virtual void print_on(outputStream* st) const;
258
259 void verify();
260 void verify_guard();
261
262 // val_equals -> it will check that all cards covered by mr equal val
263 // !val_equals -> it will check that all cards covered by mr do not equal val
264 void verify_region(MemRegion mr, CardValue val, bool val_equals) PRODUCT_RETURN;
265 void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
266 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
267 };
268
269 #endif // SHARE_GC_SHARED_CARDTABLE_HPP