1 // Copyright 2011 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 "v8.h"
29
30 #include "zone-inl.h"
31 #include "splay-tree-inl.h"
32
33 namespace v8 {
34 namespace internal {
35
36
Zone()37 Zone::Zone()
38 : zone_excess_limit_(256 * MB),
39 segment_bytes_allocated_(0),
40 position_(0),
41 limit_(0),
42 scope_nesting_(0),
43 segment_head_(NULL) {
44 }
45 unsigned Zone::allocation_size_ = 0;
46
47
~ZoneScope()48 ZoneScope::~ZoneScope() {
49 ASSERT_EQ(Isolate::Current(), isolate_);
50 if (ShouldDeleteOnExit()) isolate_->zone()->DeleteAll();
51 isolate_->zone()->scope_nesting_--;
52 }
53
54
55 // Segments represent chunks of memory: They have starting address
56 // (encoded in the this pointer) and a size in bytes. Segments are
57 // chained together forming a LIFO structure with the newest segment
58 // available as segment_head_. Segments are allocated using malloc()
59 // and de-allocated using free().
60
61 class Segment {
62 public:
next() const63 Segment* next() const { return next_; }
clear_next()64 void clear_next() { next_ = NULL; }
65
size() const66 int size() const { return size_; }
capacity() const67 int capacity() const { return size_ - sizeof(Segment); }
68
start() const69 Address start() const { return address(sizeof(Segment)); }
end() const70 Address end() const { return address(size_); }
71
72 private:
73 // Computes the address of the nth byte in this segment.
address(int n) const74 Address address(int n) const {
75 return Address(this) + n;
76 }
77
78 Segment* next_;
79 int size_;
80
81 friend class Zone;
82 };
83
84
85 // Creates a new segment, sets it size, and pushes it to the front
86 // of the segment chain. Returns the new segment.
NewSegment(int size)87 Segment* Zone::NewSegment(int size) {
88 Segment* result = reinterpret_cast<Segment*>(Malloced::New(size));
89 adjust_segment_bytes_allocated(size);
90 if (result != NULL) {
91 result->next_ = segment_head_;
92 result->size_ = size;
93 segment_head_ = result;
94 }
95 return result;
96 }
97
98
99 // Deletes the given segment. Does not touch the segment chain.
DeleteSegment(Segment * segment,int size)100 void Zone::DeleteSegment(Segment* segment, int size) {
101 adjust_segment_bytes_allocated(-size);
102 Malloced::Delete(segment);
103 }
104
105
DeleteAll()106 void Zone::DeleteAll() {
107 #ifdef DEBUG
108 // Constant byte value used for zapping dead memory in debug mode.
109 static const unsigned char kZapDeadByte = 0xcd;
110 #endif
111
112 // Find a segment with a suitable size to keep around.
113 Segment* keep = segment_head_;
114 while (keep != NULL && keep->size() > kMaximumKeptSegmentSize) {
115 keep = keep->next();
116 }
117
118 // Traverse the chained list of segments, zapping (in debug mode)
119 // and freeing every segment except the one we wish to keep.
120 Segment* current = segment_head_;
121 while (current != NULL) {
122 Segment* next = current->next();
123 if (current == keep) {
124 // Unlink the segment we wish to keep from the list.
125 current->clear_next();
126 } else {
127 int size = current->size();
128 #ifdef DEBUG
129 // Zap the entire current segment (including the header).
130 memset(current, kZapDeadByte, size);
131 #endif
132 DeleteSegment(current, size);
133 }
134 current = next;
135 }
136
137 // If we have found a segment we want to keep, we must recompute the
138 // variables 'position' and 'limit' to prepare for future allocate
139 // attempts. Otherwise, we must clear the position and limit to
140 // force a new segment to be allocated on demand.
141 if (keep != NULL) {
142 Address start = keep->start();
143 position_ = RoundUp(start, kAlignment);
144 limit_ = keep->end();
145 #ifdef DEBUG
146 // Zap the contents of the kept segment (but not the header).
147 memset(start, kZapDeadByte, keep->capacity());
148 #endif
149 } else {
150 position_ = limit_ = 0;
151 }
152
153 // Update the head segment to be the kept segment (if any).
154 segment_head_ = keep;
155 }
156
157
NewExpand(int size)158 Address Zone::NewExpand(int size) {
159 // Make sure the requested size is already properly aligned and that
160 // there isn't enough room in the Zone to satisfy the request.
161 ASSERT(size == RoundDown(size, kAlignment));
162 ASSERT(position_ + size > limit_);
163
164 // Compute the new segment size. We use a 'high water mark'
165 // strategy, where we increase the segment size every time we expand
166 // except that we employ a maximum segment size when we delete. This
167 // is to avoid excessive malloc() and free() overhead.
168 Segment* head = segment_head_;
169 int old_size = (head == NULL) ? 0 : head->size();
170 static const int kSegmentOverhead = sizeof(Segment) + kAlignment;
171 int new_size = kSegmentOverhead + size + (old_size << 1);
172 if (new_size < kMinimumSegmentSize) {
173 new_size = kMinimumSegmentSize;
174 } else if (new_size > kMaximumSegmentSize) {
175 // Limit the size of new segments to avoid growing the segment size
176 // exponentially, thus putting pressure on contiguous virtual address space.
177 // All the while making sure to allocate a segment large enough to hold the
178 // requested size.
179 new_size = Max(kSegmentOverhead + size, kMaximumSegmentSize);
180 }
181 Segment* segment = NewSegment(new_size);
182 if (segment == NULL) {
183 V8::FatalProcessOutOfMemory("Zone");
184 return NULL;
185 }
186
187 // Recompute 'top' and 'limit' based on the new segment.
188 Address result = RoundUp(segment->start(), kAlignment);
189 position_ = result + size;
190 limit_ = segment->end();
191 ASSERT(position_ <= limit_);
192 return result;
193 }
194
195
196 } } // namespace v8::internal
197