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(Isolate* isolate) 71 : allocation_size_(0), 72 segment_bytes_allocated_(0), 73 position_(0), 74 limit_(0), 75 segment_head_(NULL), 76 isolate_(isolate) { 77 } 78 79 80 Zone::~Zone() { 81 DeleteAll(); 82 DeleteKeptSegment(); 83 84 ASSERT(segment_bytes_allocated_ == 0); 85 } 86 87 88 void Zone::DeleteAll() { 89 #ifdef DEBUG 90 // Constant byte value used for zapping dead memory in debug mode. 91 static const unsigned char kZapDeadByte = 0xcd; 92 #endif 93 94 // Find a segment with a suitable size to keep around. 95 Segment* keep = NULL; 96 // Traverse the chained list of segments, zapping (in debug mode) 97 // and freeing every segment except the one we wish to keep. 98 for (Segment* current = segment_head_; current != NULL; ) { 99 Segment* next = current->next(); 100 if (keep == NULL && current->size() <= kMaximumKeptSegmentSize) { 101 // Unlink the segment we wish to keep from the list. 102 keep = current; 103 keep->clear_next(); 104 } else { 105 int size = current->size(); 106 #ifdef DEBUG 107 // Zap the entire current segment (including the header). 108 memset(current, kZapDeadByte, size); 109 #endif 110 DeleteSegment(current, size); 111 } 112 current = next; 113 } 114 115 // If we have found a segment we want to keep, we must recompute the 116 // variables 'position' and 'limit' to prepare for future allocate 117 // attempts. Otherwise, we must clear the position and limit to 118 // force a new segment to be allocated on demand. 119 if (keep != NULL) { 120 Address start = keep->start(); 121 position_ = RoundUp(start, kAlignment); 122 limit_ = keep->end(); 123 #ifdef DEBUG 124 // Zap the contents of the kept segment (but not the header). 125 memset(start, kZapDeadByte, keep->capacity()); 126 #endif 127 } else { 128 position_ = limit_ = 0; 129 } 130 131 // Update the head segment to be the kept segment (if any). 132 segment_head_ = keep; 133 } 134 135 136 void Zone::DeleteKeptSegment() { 137 #ifdef DEBUG 138 // Constant byte value used for zapping dead memory in debug mode. 139 static const unsigned char kZapDeadByte = 0xcd; 140 #endif 141 142 ASSERT(segment_head_ == NULL || segment_head_->next() == NULL); 143 if (segment_head_ != NULL) { 144 int size = segment_head_->size(); 145 #ifdef DEBUG 146 // Zap the entire kept segment (including the header). 147 memset(segment_head_, kZapDeadByte, size); 148 #endif 149 DeleteSegment(segment_head_, size); 150 segment_head_ = NULL; 151 } 152 153 ASSERT(segment_bytes_allocated_ == 0); 154 } 155 156 157 // Creates a new segment, sets it size, and pushes it to the front 158 // of the segment chain. Returns the new segment. 159 Segment* Zone::NewSegment(int size) { 160 Segment* result = reinterpret_cast<Segment*>(Malloced::New(size)); 161 adjust_segment_bytes_allocated(size); 162 if (result != NULL) { 163 result->Initialize(segment_head_, size); 164 segment_head_ = result; 165 } 166 return result; 167 } 168 169 170 // Deletes the given segment. Does not touch the segment chain. 171 void Zone::DeleteSegment(Segment* segment, int size) { 172 adjust_segment_bytes_allocated(-size); 173 Malloced::Delete(segment); 174 } 175 176 177 Address Zone::NewExpand(int size) { 178 // Make sure the requested size is already properly aligned and that 179 // there isn't enough room in the Zone to satisfy the request. 180 ASSERT(size == RoundDown(size, kAlignment)); 181 ASSERT(size > limit_ - position_); 182 183 // Compute the new segment size. We use a 'high water mark' 184 // strategy, where we increase the segment size every time we expand 185 // except that we employ a maximum segment size when we delete. This 186 // is to avoid excessive malloc() and free() overhead. 187 Segment* head = segment_head_; 188 int old_size = (head == NULL) ? 0 : head->size(); 189 static const int kSegmentOverhead = sizeof(Segment) + kAlignment; 190 int new_size_no_overhead = size + (old_size << 1); 191 int new_size = kSegmentOverhead + new_size_no_overhead; 192 // Guard against integer overflow. 193 if (new_size_no_overhead < size || new_size < kSegmentOverhead) { 194 V8::FatalProcessOutOfMemory("Zone"); 195 return NULL; 196 } 197 if (new_size < kMinimumSegmentSize) { 198 new_size = kMinimumSegmentSize; 199 } else if (new_size > kMaximumSegmentSize) { 200 // Limit the size of new segments to avoid growing the segment size 201 // exponentially, thus putting pressure on contiguous virtual address space. 202 // All the while making sure to allocate a segment large enough to hold the 203 // requested size. 204 new_size = Max(kSegmentOverhead + size, kMaximumSegmentSize); 205 } 206 Segment* segment = NewSegment(new_size); 207 if (segment == NULL) { 208 V8::FatalProcessOutOfMemory("Zone"); 209 return NULL; 210 } 211 212 // Recompute 'top' and 'limit' based on the new segment. 213 Address result = RoundUp(segment->start(), kAlignment); 214 position_ = result + size; 215 // Check for address overflow. 216 if (position_ < result) { 217 V8::FatalProcessOutOfMemory("Zone"); 218 return NULL; 219 } 220 limit_ = segment->end(); 221 ASSERT(position_ <= limit_); 222 return result; 223 } 224 225 226 } } // namespace v8::internal 227