1 // Copyright 2012 the V8 project authors. All rights reserved. 2 // Redistribution and use in source and binary forms, with or without 3 // modification, are permitted provided that the following conditions are 4 // met: 5 // 6 // * Redistributions of source code must retain the above copyright 7 // notice, this list of conditions and the following disclaimer. 8 // * Redistributions in binary form must reproduce the above 9 // copyright notice, this list of conditions and the following 10 // disclaimer in the documentation and/or other materials provided 11 // with the distribution. 12 // * Neither the name of Google Inc. nor the names of its 13 // contributors may be used to endorse or promote products derived 14 // from this software without specific prior written permission. 15 // 16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 28 #include <string.h> 29 30 #include "v8.h" 31 #include "zone-inl.h" 32 33 namespace v8 { 34 namespace internal { 35 36 37 // Segments represent chunks of memory: They have starting address 38 // (encoded in the this pointer) and a size in bytes. Segments are 39 // chained together forming a LIFO structure with the newest segment 40 // available as segment_head_. Segments are allocated using malloc() 41 // and de-allocated using free(). 42 43 class Segment { 44 public: 45 void Initialize(Segment* next, int size) { 46 next_ = next; 47 size_ = size; 48 } 49 50 Segment* next() const { return next_; } 51 void clear_next() { next_ = NULL; } 52 53 int size() const { return size_; } 54 int capacity() const { return size_ - sizeof(Segment); } 55 56 Address start() const { return address(sizeof(Segment)); } 57 Address end() const { return address(size_); } 58 59 private: 60 // Computes the address of the nth byte in this segment. 61 Address address(int n) const { 62 return Address(this) + n; 63 } 64 65 Segment* next_; 66 int size_; 67 }; 68 69 70 Zone::Zone() 71 : zone_excess_limit_(256 * MB), 72 segment_bytes_allocated_(0), 73 position_(0), 74 limit_(0), 75 scope_nesting_(0), 76 segment_head_(NULL) { 77 } 78 unsigned Zone::allocation_size_ = 0; 79 80 ZoneScope::~ZoneScope() { 81 ASSERT_EQ(Isolate::Current(), isolate_); 82 if (ShouldDeleteOnExit()) isolate_->zone()->DeleteAll(); 83 isolate_->zone()->scope_nesting_--; 84 } 85 86 87 // Creates a new segment, sets it size, and pushes it to the front 88 // of the segment chain. Returns the new segment. 89 Segment* Zone::NewSegment(int size) { 90 Segment* result = reinterpret_cast<Segment*>(Malloced::New(size)); 91 adjust_segment_bytes_allocated(size); 92 if (result != NULL) { 93 result->Initialize(segment_head_, size); 94 segment_head_ = result; 95 } 96 return result; 97 } 98 99 100 // Deletes the given segment. Does not touch the segment chain. 101 void Zone::DeleteSegment(Segment* segment, int size) { 102 adjust_segment_bytes_allocated(-size); 103 Malloced::Delete(segment); 104 } 105 106 107 void Zone::DeleteAll() { 108 #ifdef DEBUG 109 // Constant byte value used for zapping dead memory in debug mode. 110 static const unsigned char kZapDeadByte = 0xcd; 111 #endif 112 113 // Find a segment with a suitable size to keep around. 114 Segment* keep = segment_head_; 115 while (keep != NULL && keep->size() > kMaximumKeptSegmentSize) { 116 keep = keep->next(); 117 } 118 119 // Traverse the chained list of segments, zapping (in debug mode) 120 // and freeing every segment except the one we wish to keep. 121 Segment* current = segment_head_; 122 while (current != NULL) { 123 Segment* next = current->next(); 124 if (current == keep) { 125 // Unlink the segment we wish to keep from the list. 126 current->clear_next(); 127 } else { 128 int size = current->size(); 129 #ifdef DEBUG 130 // Zap the entire current segment (including the header). 131 memset(current, kZapDeadByte, size); 132 #endif 133 DeleteSegment(current, size); 134 } 135 current = next; 136 } 137 138 // If we have found a segment we want to keep, we must recompute the 139 // variables 'position' and 'limit' to prepare for future allocate 140 // attempts. Otherwise, we must clear the position and limit to 141 // force a new segment to be allocated on demand. 142 if (keep != NULL) { 143 Address start = keep->start(); 144 position_ = RoundUp(start, kAlignment); 145 limit_ = keep->end(); 146 #ifdef DEBUG 147 // Zap the contents of the kept segment (but not the header). 148 memset(start, kZapDeadByte, keep->capacity()); 149 #endif 150 } else { 151 position_ = limit_ = 0; 152 } 153 154 // Update the head segment to be the kept segment (if any). 155 segment_head_ = keep; 156 } 157 158 159 void Zone::DeleteKeptSegment() { 160 if (segment_head_ != NULL) { 161 DeleteSegment(segment_head_, segment_head_->size()); 162 segment_head_ = NULL; 163 } 164 } 165 166 167 Address Zone::NewExpand(int size) { 168 // Make sure the requested size is already properly aligned and that 169 // there isn't enough room in the Zone to satisfy the request. 170 ASSERT(size == RoundDown(size, kAlignment)); 171 ASSERT(size > limit_ - position_); 172 173 // Compute the new segment size. We use a 'high water mark' 174 // strategy, where we increase the segment size every time we expand 175 // except that we employ a maximum segment size when we delete. This 176 // is to avoid excessive malloc() and free() overhead. 177 Segment* head = segment_head_; 178 int old_size = (head == NULL) ? 0 : head->size(); 179 static const int kSegmentOverhead = sizeof(Segment) + kAlignment; 180 int new_size_no_overhead = size + (old_size << 1); 181 int new_size = kSegmentOverhead + new_size_no_overhead; 182 // Guard against integer overflow. 183 if (new_size_no_overhead < size || new_size < kSegmentOverhead) { 184 V8::FatalProcessOutOfMemory("Zone"); 185 return NULL; 186 } 187 if (new_size < kMinimumSegmentSize) { 188 new_size = kMinimumSegmentSize; 189 } else if (new_size > kMaximumSegmentSize) { 190 // Limit the size of new segments to avoid growing the segment size 191 // exponentially, thus putting pressure on contiguous virtual address space. 192 // All the while making sure to allocate a segment large enough to hold the 193 // requested size. 194 new_size = Max(kSegmentOverhead + size, kMaximumSegmentSize); 195 } 196 Segment* segment = NewSegment(new_size); 197 if (segment == NULL) { 198 V8::FatalProcessOutOfMemory("Zone"); 199 return NULL; 200 } 201 202 // Recompute 'top' and 'limit' based on the new segment. 203 Address result = RoundUp(segment->start(), kAlignment); 204 position_ = result + size; 205 // Check for address overflow. 206 if (position_ < result) { 207 V8::FatalProcessOutOfMemory("Zone"); 208 return NULL; 209 } 210 limit_ = segment->end(); 211 ASSERT(position_ <= limit_); 212 return result; 213 } 214 215 216 } } // namespace v8::internal 217