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:
Initialize(Segment * next,int size)45 void Initialize(Segment* next, int size) {
46 next_ = next;
47 size_ = size;
48 }
49
next() const50 Segment* next() const { return next_; }
clear_next()51 void clear_next() { next_ = NULL; }
52
size() const53 int size() const { return size_; }
capacity() const54 int capacity() const { return size_ - sizeof(Segment); }
55
start() const56 Address start() const { return address(sizeof(Segment)); }
end() const57 Address end() const { return address(size_); }
58
59 private:
60 // Computes the address of the nth byte in this segment.
address(int n) const61 Address address(int n) const {
62 return Address(this) + n;
63 }
64
65 Segment* next_;
66 int size_;
67 };
68
69
Zone()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
~ZoneScope()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.
NewSegment(int size)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.
DeleteSegment(Segment * segment,int size)101 void Zone::DeleteSegment(Segment* segment, int size) {
102 adjust_segment_bytes_allocated(-size);
103 Malloced::Delete(segment);
104 }
105
106
DeleteAll()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
DeleteKeptSegment()159 void Zone::DeleteKeptSegment() {
160 if (segment_head_ != NULL) {
161 DeleteSegment(segment_head_, segment_head_->size());
162 segment_head_ = NULL;
163 }
164 }
165
166
NewExpand(int size)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