1 /*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #ifndef ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_INL_H_
18 #define ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_INL_H_
19
20 #include "card_table.h"
21
22 #include <android-base/logging.h>
23
24 #include "base/atomic.h"
25 #include "base/bit_utils.h"
26 #include "base/mem_map.h"
27 #include "space_bitmap.h"
28
29 namespace art {
30 namespace gc {
31 namespace accounting {
32
byte_cas(uint8_t old_value,uint8_t new_value,uint8_t * address)33 static inline bool byte_cas(uint8_t old_value, uint8_t new_value, uint8_t* address) {
34 #if defined(__i386__) || defined(__x86_64__)
35 Atomic<uint8_t>* byte_atomic = reinterpret_cast<Atomic<uint8_t>*>(address);
36 return byte_atomic->CompareAndSetWeakRelaxed(old_value, new_value);
37 #else
38 // Little endian means most significant byte is on the left.
39 const size_t shift_in_bytes = reinterpret_cast<uintptr_t>(address) % sizeof(uintptr_t);
40 // Align the address down.
41 address -= shift_in_bytes;
42 const size_t shift_in_bits = shift_in_bytes * kBitsPerByte;
43 Atomic<uintptr_t>* word_atomic = reinterpret_cast<Atomic<uintptr_t>*>(address);
44
45 // Word with the byte we are trying to cas cleared.
46 const uintptr_t cur_word = word_atomic->load(std::memory_order_relaxed) &
47 ~(static_cast<uintptr_t>(0xFF) << shift_in_bits);
48 const uintptr_t old_word = cur_word | (static_cast<uintptr_t>(old_value) << shift_in_bits);
49 const uintptr_t new_word = cur_word | (static_cast<uintptr_t>(new_value) << shift_in_bits);
50 return word_atomic->CompareAndSetWeakRelaxed(old_word, new_word);
51 #endif
52 }
53
54 template <bool kClearCard, typename Visitor>
Scan(ContinuousSpaceBitmap * bitmap,uint8_t * const scan_begin,uint8_t * const scan_end,const Visitor & visitor,const uint8_t minimum_age)55 inline size_t CardTable::Scan(ContinuousSpaceBitmap* bitmap,
56 uint8_t* const scan_begin,
57 uint8_t* const scan_end,
58 const Visitor& visitor,
59 const uint8_t minimum_age) {
60 DCHECK_GE(scan_begin, reinterpret_cast<uint8_t*>(bitmap->HeapBegin()));
61 // scan_end is the byte after the last byte we scan.
62 DCHECK_LE(scan_end, reinterpret_cast<uint8_t*>(bitmap->HeapLimit()));
63 uint8_t* const card_begin = CardFromAddr(scan_begin);
64 uint8_t* const card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
65 uint8_t* card_cur = card_begin;
66 CheckCardValid(card_cur);
67 CheckCardValid(card_end);
68 size_t cards_scanned = 0;
69
70 // Handle any unaligned cards at the start.
71 while (!IsAligned<sizeof(intptr_t)>(card_cur) && card_cur < card_end) {
72 if (*card_cur >= minimum_age) {
73 uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
74 bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
75 ++cards_scanned;
76 }
77 ++card_cur;
78 }
79
80 uint8_t* aligned_end = card_end -
81 (reinterpret_cast<uintptr_t>(card_end) & (sizeof(uintptr_t) - 1));
82
83 uintptr_t* word_end = reinterpret_cast<uintptr_t*>(aligned_end);
84 for (uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur); word_cur < word_end;
85 ++word_cur) {
86 while (LIKELY(*word_cur == 0)) {
87 ++word_cur;
88 if (UNLIKELY(word_cur >= word_end)) {
89 goto exit_for;
90 }
91 }
92
93 // Find the first dirty card.
94 uintptr_t start_word = *word_cur;
95 uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(reinterpret_cast<uint8_t*>(word_cur)));
96 // TODO: Investigate if processing continuous runs of dirty cards with a single bitmap visit is
97 // more efficient.
98 for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
99 if (static_cast<uint8_t>(start_word) >= minimum_age) {
100 auto* card = reinterpret_cast<uint8_t*>(word_cur) + i;
101 DCHECK(*card == static_cast<uint8_t>(start_word) || *card == kCardDirty)
102 << "card " << static_cast<size_t>(*card) << " intptr_t " << (start_word & 0xFF);
103 bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
104 ++cards_scanned;
105 }
106 start_word >>= 8;
107 start += kCardSize;
108 }
109 }
110 exit_for:
111
112 // Handle any unaligned cards at the end.
113 card_cur = reinterpret_cast<uint8_t*>(word_end);
114 while (card_cur < card_end) {
115 if (*card_cur >= minimum_age) {
116 uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
117 bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
118 ++cards_scanned;
119 }
120 ++card_cur;
121 }
122
123 if (kClearCard) {
124 ClearCardRange(scan_begin, scan_end);
125 }
126
127 return cards_scanned;
128 }
129
130 template <typename Visitor, typename ModifiedVisitor>
ModifyCardsAtomic(uint8_t * scan_begin,uint8_t * scan_end,const Visitor & visitor,const ModifiedVisitor & modified)131 inline void CardTable::ModifyCardsAtomic(uint8_t* scan_begin,
132 uint8_t* scan_end,
133 const Visitor& visitor,
134 const ModifiedVisitor& modified) {
135 uint8_t* card_cur = CardFromAddr(scan_begin);
136 uint8_t* card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
137 CheckCardValid(card_cur);
138 CheckCardValid(card_end);
139 DCHECK(visitor(kCardClean) == kCardClean);
140
141 // Handle any unaligned cards at the start.
142 while (!IsAligned<sizeof(intptr_t)>(card_cur) && card_cur < card_end) {
143 uint8_t expected, new_value;
144 do {
145 expected = *card_cur;
146 new_value = visitor(expected);
147 } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_cur)));
148 if (expected != new_value) {
149 modified(card_cur, expected, new_value);
150 }
151 ++card_cur;
152 }
153
154 // Handle unaligned cards at the end.
155 while (!IsAligned<sizeof(intptr_t)>(card_end) && card_end > card_cur) {
156 --card_end;
157 uint8_t expected, new_value;
158 do {
159 expected = *card_end;
160 new_value = visitor(expected);
161 } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_end)));
162 if (expected != new_value) {
163 modified(card_end, expected, new_value);
164 }
165 }
166
167 // Now we have the words, we can process words in parallel.
168 uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur);
169 uintptr_t* word_end = reinterpret_cast<uintptr_t*>(card_end);
170 // TODO: This is not big endian safe.
171 union {
172 uintptr_t expected_word;
173 uint8_t expected_bytes[sizeof(uintptr_t)];
174 };
175 union {
176 uintptr_t new_word;
177 uint8_t new_bytes[sizeof(uintptr_t)];
178 };
179
180 // TODO: Parallelize.
181 while (word_cur < word_end) {
182 while (true) {
183 expected_word = *word_cur;
184 static_assert(kCardClean == 0);
185 if (LIKELY(expected_word == 0 /* All kCardClean */ )) {
186 break;
187 }
188 for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
189 new_bytes[i] = visitor(expected_bytes[i]);
190 }
191 Atomic<uintptr_t>* atomic_word = reinterpret_cast<Atomic<uintptr_t>*>(word_cur);
192 if (LIKELY(atomic_word->CompareAndSetWeakRelaxed(expected_word, new_word))) {
193 for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
194 const uint8_t expected_byte = expected_bytes[i];
195 const uint8_t new_byte = new_bytes[i];
196 if (expected_byte != new_byte) {
197 modified(reinterpret_cast<uint8_t*>(word_cur) + i, expected_byte, new_byte);
198 }
199 }
200 break;
201 }
202 }
203 ++word_cur;
204 }
205 }
206
AddrFromCard(const uint8_t * card_addr)207 inline void* CardTable::AddrFromCard(const uint8_t *card_addr) const {
208 DCHECK(IsValidCard(card_addr))
209 << " card_addr: " << reinterpret_cast<const void*>(card_addr)
210 << " begin: " << reinterpret_cast<void*>(mem_map_.Begin() + offset_)
211 << " end: " << reinterpret_cast<void*>(mem_map_.End());
212 uintptr_t offset = card_addr - biased_begin_;
213 return reinterpret_cast<void*>(offset << kCardShift);
214 }
215
CardFromAddr(const void * addr)216 inline uint8_t* CardTable::CardFromAddr(const void *addr) const {
217 uint8_t *card_addr = biased_begin_ + (reinterpret_cast<uintptr_t>(addr) >> kCardShift);
218 // Sanity check the caller was asking for address covered by the card table
219 DCHECK(IsValidCard(card_addr)) << "addr: " << addr
220 << " card_addr: " << reinterpret_cast<void*>(card_addr);
221 return card_addr;
222 }
223
IsValidCard(const uint8_t * card_addr)224 inline bool CardTable::IsValidCard(const uint8_t* card_addr) const {
225 uint8_t* begin = mem_map_.Begin() + offset_;
226 uint8_t* end = mem_map_.End();
227 return card_addr >= begin && card_addr < end;
228 }
229
CheckCardValid(uint8_t * card)230 inline void CardTable::CheckCardValid(uint8_t* card) const {
231 DCHECK(IsValidCard(card))
232 << " card_addr: " << reinterpret_cast<const void*>(card)
233 << " begin: " << reinterpret_cast<void*>(mem_map_.Begin() + offset_)
234 << " end: " << reinterpret_cast<void*>(mem_map_.End());
235 }
236
237 } // namespace accounting
238 } // namespace gc
239 } // namespace art
240
241 #endif // ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_INL_H_
242