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   // Check that the caller was asking for an 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