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.
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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.
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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).
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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 // The mask contains zeros in places for all other values.
107 clean_card_mask = clean_card - 31,
108
109 dirty_card = 0,
110 precleaned_card = 1,
111 claimed_card = 2,
112 deferred_card = 4,
113 last_card = 8,
114 CT_MR_BS_last_reserved = 16
115 };
116
117 // a word's worth (row) of clean card values
118 static const intptr_t clean_card_row = (intptr_t)(-1);
119
120 public:
121 CardTable(MemRegion whole_heap, bool conc_scan);
122 virtual ~CardTable();
123 virtual void initialize();
124
125 // The kinds of precision a CardTable may offer.
126 enum PrecisionStyle {
127 Precise,
128 ObjHeadPreciseArray
129 };
130
131 // Tells what style of precision this card table offers.
132 PrecisionStyle precision() {
133 return ObjHeadPreciseArray; // Only one supported for now.
134 }
135
136 // *** Barrier set functions.
137
138 // Initialization utilities; covered_words is the size of the covered region
139 // in, um, words.
140 inline size_t cards_required(size_t covered_words) {
141 // Add one for a guard card, used to detect errors.
142 const size_t words = align_up(covered_words, card_size_in_words);
143 return words / card_size_in_words + 1;
144 }
145
146 // Dirty the bytes corresponding to "mr" (not all of which must be
147 // covered.)
148 void dirty_MemRegion(MemRegion mr);
149
150 // Clear (to clean_card) the bytes entirely contained within "mr" (not
151 // all of which must be covered.)
152 void clear_MemRegion(MemRegion mr);
153
154 // Return true if "p" is at the start of a card.
155 bool is_card_aligned(HeapWord* p) {
156 CardValue* pcard = byte_for(p);
157 return (addr_for(pcard) == p);
158 }
159
160 // Mapping from address to card marking array entry
161 CardValue* byte_for(const void* p) const {
162 assert(_whole_heap.contains(p),
163 "Attempt to access p = " PTR_FORMAT " out of bounds of "
164 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
165 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
166 CardValue* result = &_byte_map_base[uintptr_t(p) >> card_shift];
167 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
168 "out of bounds accessor for card marking array");
169 return result;
170 }
171
172 // The card table byte one after the card marking array
173 // entry for argument address. Typically used for higher bounds
174 // for loops iterating through the card table.
175 CardValue* byte_after(const void* p) const {
176 return byte_for(p) + 1;
177 }
178
179 virtual void invalidate(MemRegion mr);
180 void clear(MemRegion mr);
181 void dirty(MemRegion mr);
182
183 // Provide read-only access to the card table array.
184 const CardValue* byte_for_const(const void* p) const {
185 return byte_for(p);
186 }
187 const CardValue* byte_after_const(const void* p) const {
188 return byte_after(p);
189 }
190
191 // Mapping from card marking array entry to address of first word
192 HeapWord* addr_for(const CardValue* p) const {
193 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
194 "out of bounds access to card marking array. p: " PTR_FORMAT
195 " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
196 p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
197 size_t delta = pointer_delta(p, _byte_map_base, sizeof(CardValue));
198 HeapWord* result = (HeapWord*) (delta << card_shift);
199 assert(_whole_heap.contains(result),
200 "Returning result = " PTR_FORMAT " out of bounds of "
201 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
202 p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
203 return result;
204 }
205
206 // Mapping from address to card marking array index.
207 size_t index_for(void* p) {
208 assert(_whole_heap.contains(p),
209 "Attempt to access p = " PTR_FORMAT " out of bounds of "
210 " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
211 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
212 return byte_for(p) - _byte_map;
213 }
214
215 CardValue* byte_for_index(const size_t card_index) const {
216 return _byte_map + card_index;
217 }
218
219 // Resize one of the regions covered by the remembered set.
220 virtual void resize_covered_region(MemRegion new_region);
221
222 // *** Card-table-RemSet-specific things.
223
224 static uintx ct_max_alignment_constraint();
225
226 // Apply closure "cl" to the dirty cards containing some part of
227 // MemRegion "mr".
228 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
229
230 // Return the MemRegion corresponding to the first maximal run
231 // of dirty cards lying completely within MemRegion mr.
232 // If reset is "true", then sets those card table entries to the given
233 // value.
234 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
235 int reset_val);
236
237 // Constants
238 enum SomePublicConstants {
239 card_shift = 9,
240 card_size = 1 << card_shift,
241 card_size_in_words = card_size / sizeof(HeapWord)
242 };
243
244 static CardValue clean_card_val() { return clean_card; }
245 static CardValue clean_card_mask_val() { return clean_card_mask; }
246 static CardValue dirty_card_val() { return dirty_card; }
247 static CardValue claimed_card_val() { return claimed_card; }
248 static CardValue precleaned_card_val() { return precleaned_card; }
249 static CardValue deferred_card_val() { return deferred_card; }
250 static intptr_t clean_card_row_val() { return clean_card_row; }
251
252 // Card marking array base (adjusted for heap low boundary)
253 // This would be the 0th element of _byte_map, if the heap started at 0x0.
254 // But since the heap starts at some higher address, this points to somewhere
255 // before the beginning of the actual _byte_map.
256 CardValue* byte_map_base() const { return _byte_map_base; }
257 bool scanned_concurrently() const { return _scanned_concurrently; }
258
259 virtual bool is_in_young(oop obj) const = 0;
260
261 // Print a description of the memory for the card table
262 virtual void print_on(outputStream* st) const;
263
264 void verify();
265 void verify_guard();
266
267 // val_equals -> it will check that all cards covered by mr equal val
268 // !val_equals -> it will check that all cards covered by mr do not equal val
269 void verify_region(MemRegion mr, CardValue val, bool val_equals) PRODUCT_RETURN;
270 void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
271 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
272 };
273
274 #endif // SHARE_GC_SHARED_CARDTABLE_HPP