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      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,
     54                               uint8_t* const scan_begin,
     55                               uint8_t* const scan_end,
     56                               const Visitor& visitor,
     57                               const uint8_t minimum_age) {
     58   DCHECK_GE(scan_begin, reinterpret_cast<uint8_t*>(bitmap->HeapBegin()));
     59   // scan_end is the byte after the last byte we scan.
     60   DCHECK_LE(scan_end, reinterpret_cast<uint8_t*>(bitmap->HeapLimit()));
     61   uint8_t* const card_begin = CardFromAddr(scan_begin);
     62   uint8_t* const card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
     63   uint8_t* card_cur = card_begin;
     64   CheckCardValid(card_cur);
     65   CheckCardValid(card_end);
     66   size_t cards_scanned = 0;
     67 
     68   // Handle any unaligned cards at the start.
     69   while (!IsAligned<sizeof(intptr_t)>(card_cur) && card_cur < card_end) {
     70     if (*card_cur >= minimum_age) {
     71       uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
     72       bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
     73       ++cards_scanned;
     74     }
     75     ++card_cur;
     76   }
     77 
     78   uint8_t* aligned_end = card_end -
     79       (reinterpret_cast<uintptr_t>(card_end) & (sizeof(uintptr_t) - 1));
     80 
     81   uintptr_t* word_end = reinterpret_cast<uintptr_t*>(aligned_end);
     82   for (uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur); word_cur < word_end;
     83       ++word_cur) {
     84     while (LIKELY(*word_cur == 0)) {
     85       ++word_cur;
     86       if (UNLIKELY(word_cur >= word_end)) {
     87         goto exit_for;
     88       }
     89     }
     90 
     91     // Find the first dirty card.
     92     uintptr_t start_word = *word_cur;
     93     uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(reinterpret_cast<uint8_t*>(word_cur)));
     94     // TODO: Investigate if processing continuous runs of dirty cards with a single bitmap visit is
     95     // more efficient.
     96     for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
     97       if (static_cast<uint8_t>(start_word) >= minimum_age) {
     98         auto* card = reinterpret_cast<uint8_t*>(word_cur) + i;
     99         DCHECK(*card == static_cast<uint8_t>(start_word) || *card == kCardDirty)
    100             << "card " << static_cast<size_t>(*card) << " intptr_t " << (start_word & 0xFF);
    101         bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
    102         ++cards_scanned;
    103       }
    104       start_word >>= 8;
    105       start += kCardSize;
    106     }
    107   }
    108   exit_for:
    109 
    110   // Handle any unaligned cards at the end.
    111   card_cur = reinterpret_cast<uint8_t*>(word_end);
    112   while (card_cur < card_end) {
    113     if (*card_cur >= minimum_age) {
    114       uintptr_t start = reinterpret_cast<uintptr_t>(AddrFromCard(card_cur));
    115       bitmap->VisitMarkedRange(start, start + kCardSize, visitor);
    116       ++cards_scanned;
    117     }
    118     ++card_cur;
    119   }
    120 
    121   if (kClearCard) {
    122     ClearCardRange(scan_begin, scan_end);
    123   }
    124 
    125   return cards_scanned;
    126 }
    127 
    128 /*
    129  * Visitor is expected to take in a card and return the new value. When a value is modified, the
    130  * modify visitor is called.
    131  * visitor: The visitor which modifies the cards. Returns the new value for a card given an old
    132  * value.
    133  * modified: Whenever the visitor modifies a card, this visitor is called on the card. Enables
    134  * us to know which cards got cleared.
    135  */
    136 template <typename Visitor, typename ModifiedVisitor>
    137 inline void CardTable::ModifyCardsAtomic(uint8_t* scan_begin,
    138                                          uint8_t* scan_end,
    139                                          const Visitor& visitor,
    140                                          const ModifiedVisitor& modified) {
    141   uint8_t* card_cur = CardFromAddr(scan_begin);
    142   uint8_t* card_end = CardFromAddr(AlignUp(scan_end, kCardSize));
    143   CheckCardValid(card_cur);
    144   CheckCardValid(card_end);
    145 
    146   // Handle any unaligned cards at the start.
    147   while (!IsAligned<sizeof(intptr_t)>(card_cur) && card_cur < card_end) {
    148     uint8_t expected, new_value;
    149     do {
    150       expected = *card_cur;
    151       new_value = visitor(expected);
    152     } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_cur)));
    153     if (expected != new_value) {
    154       modified(card_cur, expected, new_value);
    155     }
    156     ++card_cur;
    157   }
    158 
    159   // Handle unaligned cards at the end.
    160   while (!IsAligned<sizeof(intptr_t)>(card_end) && card_end > card_cur) {
    161     --card_end;
    162     uint8_t expected, new_value;
    163     do {
    164       expected = *card_end;
    165       new_value = visitor(expected);
    166     } while (expected != new_value && UNLIKELY(!byte_cas(expected, new_value, card_end)));
    167     if (expected != new_value) {
    168       modified(card_end, expected, new_value);
    169     }
    170   }
    171 
    172   // Now we have the words, we can process words in parallel.
    173   uintptr_t* word_cur = reinterpret_cast<uintptr_t*>(card_cur);
    174   uintptr_t* word_end = reinterpret_cast<uintptr_t*>(card_end);
    175   // TODO: This is not big endian safe.
    176   union {
    177     uintptr_t expected_word;
    178     uint8_t expected_bytes[sizeof(uintptr_t)];
    179   };
    180   union {
    181     uintptr_t new_word;
    182     uint8_t new_bytes[sizeof(uintptr_t)];
    183   };
    184 
    185   // TODO: Parallelize.
    186   while (word_cur < word_end) {
    187     while (true) {
    188       expected_word = *word_cur;
    189       if (LIKELY(expected_word == 0)) {
    190         break;
    191       }
    192       for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
    193         new_bytes[i] = visitor(expected_bytes[i]);
    194       }
    195       Atomic<uintptr_t>* atomic_word = reinterpret_cast<Atomic<uintptr_t>*>(word_cur);
    196       if (LIKELY(atomic_word->CompareExchangeWeakRelaxed(expected_word, new_word))) {
    197         for (size_t i = 0; i < sizeof(uintptr_t); ++i) {
    198           const uint8_t expected_byte = expected_bytes[i];
    199           const uint8_t new_byte = new_bytes[i];
    200           if (expected_byte != new_byte) {
    201             modified(reinterpret_cast<uint8_t*>(word_cur) + i, expected_byte, new_byte);
    202           }
    203         }
    204         break;
    205       }
    206     }
    207     ++word_cur;
    208   }
    209 }
    210 
    211 inline void* CardTable::AddrFromCard(const uint8_t *card_addr) const {
    212   DCHECK(IsValidCard(card_addr))
    213     << " card_addr: " << reinterpret_cast<const void*>(card_addr)
    214     << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
    215     << " end: " << reinterpret_cast<void*>(mem_map_->End());
    216   uintptr_t offset = card_addr - biased_begin_;
    217   return reinterpret_cast<void*>(offset << kCardShift);
    218 }
    219 
    220 inline uint8_t* CardTable::CardFromAddr(const void *addr) const {
    221   uint8_t *card_addr = biased_begin_ + (reinterpret_cast<uintptr_t>(addr) >> kCardShift);
    222   // Sanity check the caller was asking for address covered by the card table
    223   DCHECK(IsValidCard(card_addr)) << "addr: " << addr
    224       << " card_addr: " << reinterpret_cast<void*>(card_addr);
    225   return card_addr;
    226 }
    227 
    228 inline bool CardTable::IsValidCard(const uint8_t* card_addr) const {
    229   uint8_t* begin = mem_map_->Begin() + offset_;
    230   uint8_t* end = mem_map_->End();
    231   return card_addr >= begin && card_addr < end;
    232 }
    233 
    234 inline void CardTable::CheckCardValid(uint8_t* card) const {
    235   DCHECK(IsValidCard(card))
    236       << " card_addr: " << reinterpret_cast<const void*>(card)
    237       << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
    238       << " end: " << reinterpret_cast<void*>(mem_map_->End());
    239 }
    240 
    241 }  // namespace accounting
    242 }  // namespace gc
    243 }  // namespace art
    244 
    245 #endif  // ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_INL_H_
    246