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 "atomic.h"
21 #include "base/logging.h"
22 #include "card_table.h"
23 #include "space_bitmap.h"
24 #include "utils.h"
25 
26 namespace art {
27 namespace gc {
28 namespace accounting {
29 
byte_cas(byte old_value,byte new_value,byte * address)30 static inline bool byte_cas(byte old_value, byte new_value, byte* address) {
31 #if defined(__i386__) || defined(__x86_64__)
32   Atomic<byte>* byte_atomic = reinterpret_cast<Atomic<byte>*>(address);
33   return byte_atomic->CompareExchangeWeakRelaxed(old_value, new_value);
34 #else
35   // Little endian means most significant byte is on the left.
36   const size_t shift_in_bytes = reinterpret_cast<uintptr_t>(address) % sizeof(uintptr_t);
37   // Align the address down.
38   address -= shift_in_bytes;
39   const size_t shift_in_bits = shift_in_bytes * kBitsPerByte;
40   Atomic<uintptr_t>* word_atomic = reinterpret_cast<Atomic<uintptr_t>*>(address);
41 
42   // Word with the byte we are trying to cas cleared.
43   const uintptr_t cur_word = word_atomic->LoadRelaxed() &
44       ~(static_cast<uintptr_t>(0xFF) << shift_in_bits);
45   const uintptr_t old_word = cur_word | (static_cast<uintptr_t>(old_value) << shift_in_bits);
46   const uintptr_t new_word = cur_word | (static_cast<uintptr_t>(new_value) << shift_in_bits);
47   return word_atomic->CompareExchangeWeakRelaxed(old_word, new_word);
48 #endif
49 }
50 
51 template <typename Visitor>
Scan(ContinuousSpaceBitmap * bitmap,byte * scan_begin,byte * scan_end,const Visitor & visitor,const byte minimum_age)52 inline size_t CardTable::Scan(ContinuousSpaceBitmap* bitmap, byte* scan_begin, byte* scan_end,
53                               const Visitor& visitor, const byte minimum_age) const {
54   DCHECK_GE(scan_begin, reinterpret_cast<byte*>(bitmap->HeapBegin()));
55   // scan_end is the byte after the last byte we scan.
56   DCHECK_LE(scan_end, reinterpret_cast<byte*>(bitmap->HeapLimit()));
57   byte* card_cur = CardFromAddr(scan_begin);
58   byte* card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
59   CheckCardValid(card_cur);
60   CheckCardValid(card_end);
61   size_t cards_scanned = 0;
62 
63   // Handle any unaligned cards at the start.
64   while (!IsAligned<sizeof(word)>(card_cur) && card_cur < card_end) {
65     if (*card_cur >= minimum_age) {
66       uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
67       bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
68       ++cards_scanned;
69     }
70     ++card_cur;
71   }
72 
73   byte* aligned_end = card_end -
74       (reinterpret_cast<uintptr_t>(card_end) & (sizeof(uintptr_t) - 1));
75 
76   uintptr_t* word_end = reinterpret_cast<uintptr_t*>(aligned_end);
77   for (uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur); word_cur < word_end;
78       ++word_cur) {
79     while (LIKELY(*word_cur == 0)) {
80       ++word_cur;
81       if (UNLIKELY(word_cur >= word_end)) {
82         goto exit_for;
83       }
84     }
85 
86     // Find the first dirty card.
87     uintptr_t start_word = *word_cur;
88     uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(reinterpret_cast<byte*>(word_cur)));
89     // TODO: Investigate if processing continuous runs of dirty cards with a single bitmap visit is
90     // more efficient.
91     for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
92       if (static_cast<byte>(start_word) >= minimum_age) {
93         auto* card = reinterpret_cast<byte*>(word_cur) + i;
94         DCHECK(*card == static_cast<byte>(start_word) || *card == kCardDirty)
95             << "card " << static_cast<size_t>(*card) << " word " << (start_word & 0xFF);
96         bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
97         ++cards_scanned;
98       }
99       start_word >>= 8;
100       start += kCardSize;
101     }
102   }
103   exit_for:
104 
105   // Handle any unaligned cards at the end.
106   card_cur = reinterpret_cast<byte*>(word_end);
107   while (card_cur < card_end) {
108     if (*card_cur >= minimum_age) {
109       uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
110       bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
111       ++cards_scanned;
112     }
113     ++card_cur;
114   }
115 
116   return cards_scanned;
117 }
118 
119 /*
120  * Visitor is expected to take in a card and return the new value. When a value is modified, the
121  * modify visitor is called.
122  * visitor: The visitor which modifies the cards. Returns the new value for a card given an old
123  * value.
124  * modified: Whenever the visitor modifies a card, this visitor is called on the card. Enables
125  * us to know which cards got cleared.
126  */
127 template <typename Visitor, typename ModifiedVisitor>
ModifyCardsAtomic(byte * scan_begin,byte * scan_end,const Visitor & visitor,const ModifiedVisitor & modified)128 inline void CardTable::ModifyCardsAtomic(byte* scan_begin, byte* scan_end, const Visitor& visitor,
129                                          const ModifiedVisitor& modified) {
130   byte* card_cur = CardFromAddr(scan_begin);
131   byte* card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
132   CheckCardValid(card_cur);
133   CheckCardValid(card_end);
134 
135   // Handle any unaligned cards at the start.
136   while (!IsAligned<sizeof(word)>(card_cur) && card_cur < card_end) {
137     byte expected, new_value;
138     do {
139       expected = *card_cur;
140       new_value = visitor(expected);
141     } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_cur)));
142     if (expected != new_value) {
143       modified(card_cur, expected, new_value);
144     }
145     ++card_cur;
146   }
147 
148   // Handle unaligned cards at the end.
149   while (!IsAligned<sizeof(word)>(card_end) && card_end > card_cur) {
150     --card_end;
151     byte expected, new_value;
152     do {
153       expected = *card_end;
154       new_value = visitor(expected);
155     } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_end)));
156     if (expected != new_value) {
157       modified(card_end, expected, new_value);
158     }
159   }
160 
161   // Now we have the words, we can process words in parallel.
162   uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur);
163   uintptr_t* word_end = reinterpret_cast<uintptr_t*>(card_end);
164   // TODO: This is not big endian safe.
165   union {
166     uintptr_t expected_word;
167     uint8_t expected_bytes[sizeof(uintptr_t)];
168   };
169   union {
170     uintptr_t new_word;
171     uint8_t new_bytes[sizeof(uintptr_t)];
172   };
173 
174   // TODO: Parallelize.
175   while (word_cur < word_end) {
176     while (true) {
177       expected_word = *word_cur;
178       if (LIKELY(expected_word == 0)) {
179         break;
180       }
181       for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
182         new_bytes[i] = visitor(expected_bytes[i]);
183       }
184       Atomic<uintptr_t>* atomic_word = reinterpret_cast<Atomic<uintptr_t>*>(word_cur);
185       if (LIKELY(atomic_word->CompareExchangeWeakRelaxed(expected_word, new_word))) {
186         for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
187           const byte expected_byte = expected_bytes[i];
188           const byte new_byte = new_bytes[i];
189           if (expected_byte != new_byte) {
190             modified(reinterpret_cast<byte*>(word_cur) + i, expected_byte, new_byte);
191           }
192         }
193         break;
194       }
195     }
196     ++word_cur;
197   }
198 }
199 
AddrFromCard(const byte * card_addr)200 inline void* CardTable::AddrFromCard(const byte *card_addr) const {
201   DCHECK(IsValidCard(card_addr))
202     << " card_addr: " << reinterpret_cast<const void*>(card_addr)
203     << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
204     << " end: " << reinterpret_cast<void*>(mem_map_->End());
205   uintptr_t offset = card_addr - biased_begin_;
206   return reinterpret_cast<void*>(offset << kCardShift);
207 }
208 
CardFromAddr(const void * addr)209 inline byte* CardTable::CardFromAddr(const void *addr) const {
210   byte *card_addr = biased_begin_ + (reinterpret_cast<uintptr_t>(addr) >> kCardShift);
211   // Sanity check the caller was asking for address covered by the card table
212   DCHECK(IsValidCard(card_addr)) << "addr: " << addr
213       << " card_addr: " << reinterpret_cast<void*>(card_addr);
214   return card_addr;
215 }
216 
CheckCardValid(byte * card)217 inline void CardTable::CheckCardValid(byte* card) const {
218   DCHECK(IsValidCard(card))
219       << " card_addr: " << reinterpret_cast<const void*>(card)
220       << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
221       << " end: " << reinterpret_cast<void*>(mem_map_->End());
222 }
223 
224 }  // namespace accounting
225 }  // namespace gc
226 }  // namespace art
227 
228 #endif  // ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_INL_H_
229