Home | History | Annotate | Download | only in accounting 
      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/bit_utils.h"
     22 #include "base/logging.h"
     23 #include "card_table.h"
     24 #include "mem_map.h"
     25 #include "space_bitmap.h"
     26 
     27 namespace art {
     28 namespace gc {
     29 namespace accounting {
     30 
     31 static inline bool byte_cas(uint8_t old_value, uint8_t new_value, uint8_t* address) {
     32 #if defined(__i386__) || defined(__x86_64__)
     33   Atomic<uint8_t>* byte_atomic = reinterpret_cast<Atomic<uint8_t>*>(address);
     34   return byte_atomic->CompareExchangeWeakRelaxed(old_value, new_value);
     35 #else
     36   // Little endian means most significant byte is on the left.
     37   const size_t shift_in_bytes = reinterpret_cast<uintptr_t>(address) % sizeof(uintptr_t);
     38   // Align the address down.
     39   address -= shift_in_bytes;
     40   const size_t shift_in_bits = shift_in_bytes * kBitsPerByte;
     41   Atomic<uintptr_t>* word_atomic = reinterpret_cast<Atomic<uintptr_t>*>(address);
     42 
     43   // Word with the byte we are trying to cas cleared.
     44   const uintptr_t cur_word = word_atomic->LoadRelaxed() &
     45       ~(static_cast<uintptr_t>(0xFF) << shift_in_bits);
     46   const uintptr_t old_word = cur_word | (static_cast<uintptr_t>(old_value) << shift_in_bits);
     47   const uintptr_t new_word = cur_word | (static_cast<uintptr_t>(new_value) << shift_in_bits);
     48   return word_atomic->CompareExchangeWeakRelaxed(old_word, new_word);
     49 #endif
     50 }
     51 
     52 template <bool kClearCard, typename Visitor>
     53 inline size_t CardTable::Scan(ContinuousSpaceBitmap* bitmap, uint8_t* scan_begin, uint8_t* scan_end,
     54                               const Visitor& visitor, const uint8_t minimum_age) const {
     55   DCHECK_GE(scan_begin, reinterpret_cast<uint8_t*>(bitmap->HeapBegin()));
     56   // scan_end is the byte after the last byte we scan.
     57   DCHECK_LE(scan_end, reinterpret_cast<uint8_t*>(bitmap->HeapLimit()));
     58   uint8_t* card_cur = CardFromAddr(scan_begin);
     59   uint8_t* card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
     60   CheckCardValid(card_cur);
     61   CheckCardValid(card_end);
     62   size_t cards_scanned = 0;
     63 
     64   // Handle any unaligned cards at the start.
     65   while (!IsAligned<sizeof(intptr_t)>(card_cur) && card_cur < card_end) {
     66     if (*card_cur >= minimum_age) {
     67       uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
     68       bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
     69       ++cards_scanned;
     70       if (kClearCard) {
     71         *card_cur = 0;
     72       }
     73     }
     74     ++card_cur;
     75   }
     76 
     77   uint8_t* aligned_end = card_end -
     78       (reinterpret_cast<uintptr_t>(card_end) & (sizeof(uintptr_t) - 1));
     79 
     80   uintptr_t* word_end = reinterpret_cast<uintptr_t*>(aligned_end);
     81   for (uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur); word_cur < word_end;
     82       ++word_cur) {
     83     while (LIKELY(*word_cur == 0)) {
     84       ++word_cur;
     85       if (UNLIKELY(word_cur >= word_end)) {
     86         goto exit_for;
     87       }
     88     }
     89 
     90     // Find the first dirty card.
     91     uintptr_t start_word = *word_cur;
     92     uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(reinterpret_cast<uint8_t*>(word_cur)));
     93     // TODO: Investigate if processing continuous runs of dirty cards with a single bitmap visit is
     94     // more efficient.
     95     for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
     96       if (static_cast<uint8_t>(start_word) >= minimum_age) {
     97         auto* card = reinterpret_cast<uint8_t*>(word_cur) + i;
     98         DCHECK(*card == static_cast<uint8_t>(start_word) || *card == kCardDirty)
     99             << "card " << static_cast<size_t>(*card) << " intptr_t " << (start_word & 0xFF);
    100         bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
    101         ++cards_scanned;
    102         if (kClearCard) {
    103           *card = 0;
    104         }
    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       if (kClearCard) {
    120         *card_cur = 0;
    121       }
    122     }
    123     ++card_cur;
    124   }
    125 
    126   return cards_scanned;
    127 }
    128 
    129 /*
    130  * Visitor is expected to take in a card and return the new value. When a value is modified, the
    131  * modify visitor is called.
    132  * visitor: The visitor which modifies the cards. Returns the new value for a card given an old
    133  * value.
    134  * modified: Whenever the visitor modifies a card, this visitor is called on the card. Enables
    135  * us to know which cards got cleared.
    136  */
    137 template <typename Visitor, typename ModifiedVisitor>
    138 inline void CardTable::ModifyCardsAtomic(uint8_t* scan_begin, uint8_t* scan_end, const Visitor& visitor,
    139                                          const ModifiedVisitor& modified) {
    140   uint8_t* card_cur = CardFromAddr(scan_begin);
    141   uint8_t* card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
    142   CheckCardValid(card_cur);
    143   CheckCardValid(card_end);
    144 
    145   // Handle any unaligned cards at the start.
    146   while (!IsAligned<sizeof(intptr_t)>(card_cur) && card_cur < card_end) {
    147     uint8_t expected, new_value;
    148     do {
    149       expected = *card_cur;
    150       new_value = visitor(expected);
    151     } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_cur)));
    152     if (expected != new_value) {
    153       modified(card_cur, expected, new_value);
    154     }
    155     ++card_cur;
    156   }
    157 
    158   // Handle unaligned cards at the end.
    159   while (!IsAligned<sizeof(intptr_t)>(card_end) && card_end > card_cur) {
    160     --card_end;
    161     uint8_t expected, new_value;
    162     do {
    163       expected = *card_end;
    164       new_value = visitor(expected);
    165     } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_end)));
    166     if (expected != new_value) {
    167       modified(card_end, expected, new_value);
    168     }
    169   }
    170 
    171   // Now we have the words, we can process words in parallel.
    172   uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur);
    173   uintptr_t* word_end = reinterpret_cast<uintptr_t*>(card_end);
    174   // TODO: This is not big endian safe.
    175   union {
    176     uintptr_t expected_word;
    177     uint8_t expected_bytes[sizeof(uintptr_t)];
    178   };
    179   union {
    180     uintptr_t new_word;
    181     uint8_t new_bytes[sizeof(uintptr_t)];
    182   };
    183 
    184   // TODO: Parallelize.
    185   while (word_cur < word_end) {
    186     while (true) {
    187       expected_word = *word_cur;
    188       if (LIKELY(expected_word == 0)) {
    189         break;
    190       }
    191       for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
    192         new_bytes[i] = visitor(expected_bytes[i]);
    193       }
    194       Atomic<uintptr_t>* atomic_word = reinterpret_cast<Atomic<uintptr_t>*>(word_cur);
    195       if (LIKELY(atomic_word->CompareExchangeWeakRelaxed(expected_word, new_word))) {
    196         for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
    197           const uint8_t expected_byte = expected_bytes[i];
    198           const uint8_t new_byte = new_bytes[i];
    199           if (expected_byte != new_byte) {
    200             modified(reinterpret_cast<uint8_t*>(word_cur) + i, expected_byte, new_byte);
    201           }
    202         }
    203         break;
    204       }
    205     }
    206     ++word_cur;
    207   }
    208 }
    209 
    210 inline void* CardTable::AddrFromCard(const uint8_t *card_addr) const {
    211   DCHECK(IsValidCard(card_addr))
    212     << " card_addr: " << reinterpret_cast<const void*>(card_addr)
    213     << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
    214     << " end: " << reinterpret_cast<void*>(mem_map_->End());
    215   uintptr_t offset = card_addr - biased_begin_;
    216   return reinterpret_cast<void*>(offset << kCardShift);
    217 }
    218 
    219 inline uint8_t* CardTable::CardFromAddr(const void *addr) const {
    220   uint8_t *card_addr = biased_begin_ + (reinterpret_cast<uintptr_t>(addr) >> kCardShift);
    221   // Sanity check the caller was asking for address covered by the card table
    222   DCHECK(IsValidCard(card_addr)) << "addr: " << addr
    223       << " card_addr: " << reinterpret_cast<void*>(card_addr);
    224   return card_addr;
    225 }
    226 
    227 inline bool CardTable::IsValidCard(const uint8_t* card_addr) const {
    228   uint8_t* begin = mem_map_->Begin() + offset_;
    229   uint8_t* end = mem_map_->End();
    230   return card_addr >= begin && card_addr < end;
    231 }
    232 
    233 inline void CardTable::CheckCardValid(uint8_t* card) const {
    234   DCHECK(IsValidCard(card))
    235       << " card_addr: " << reinterpret_cast<const void*>(card)
    236       << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
    237       << " end: " << reinterpret_cast<void*>(mem_map_->End());
    238 }
    239 
    240 }  // namespace accounting
    241 }  // namespace gc
    242 }  // namespace art
    243 
    244 #endif  // ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_INL_H_
    245