1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
|
// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HEAP_BASIC_MEMORY_CHUNK_H_
#define V8_HEAP_BASIC_MEMORY_CHUNK_H_
#include <type_traits>
#include <unordered_map>
#include "src/base/atomic-utils.h"
#include "src/common/globals.h"
#include "src/flags/flags.h"
#include "src/heap/marking.h"
#include "src/heap/memory-chunk-layout.h"
#include "src/objects/heap-object.h"
#include "src/utils/allocation.h"
namespace v8 {
namespace internal {
class BaseSpace;
class BasicMemoryChunk {
public:
// Use with std data structures.
struct Hasher {
size_t operator()(const BasicMemoryChunk* const chunk) const {
return reinterpret_cast<size_t>(chunk) >> kPageSizeBits;
}
};
enum Flag {
NO_FLAGS = 0u,
IS_EXECUTABLE = 1u << 0,
POINTERS_TO_HERE_ARE_INTERESTING = 1u << 1,
POINTERS_FROM_HERE_ARE_INTERESTING = 1u << 2,
// A page in the from-space or a young large page that was not scavenged
// yet.
FROM_PAGE = 1u << 3,
// A page in the to-space or a young large page that was scavenged.
TO_PAGE = 1u << 4,
LARGE_PAGE = 1u << 5,
EVACUATION_CANDIDATE = 1u << 6,
NEVER_EVACUATE = 1u << 7,
// Large objects can have a progress bar in their page header. These object
// are scanned in increments and will be kept black while being scanned.
// Even if the mutator writes to them they will be kept black and a white
// to grey transition is performed in the value.
HAS_PROGRESS_BAR = 1u << 8,
// |PAGE_NEW_OLD_PROMOTION|: A page tagged with this flag has been promoted
// from new to old space during evacuation.
PAGE_NEW_OLD_PROMOTION = 1u << 9,
// |PAGE_NEW_NEW_PROMOTION|: A page tagged with this flag has been moved
// within the new space during evacuation.
PAGE_NEW_NEW_PROMOTION = 1u << 10,
// This flag is intended to be used for testing. Works only when both
// FLAG_stress_compaction and FLAG_manual_evacuation_candidates_selection
// are set. It forces the page to become an evacuation candidate at next
// candidates selection cycle.
FORCE_EVACUATION_CANDIDATE_FOR_TESTING = 1u << 11,
// This flag is intended to be used for testing.
NEVER_ALLOCATE_ON_PAGE = 1u << 12,
// The memory chunk is already logically freed, however the actual freeing
// still has to be performed.
PRE_FREED = 1u << 13,
// |POOLED|: When actually freeing this chunk, only uncommit and do not
// give up the reservation as we still reuse the chunk at some point.
POOLED = 1u << 14,
// |COMPACTION_WAS_ABORTED|: Indicates that the compaction in this page
// has been aborted and needs special handling by the sweeper.
COMPACTION_WAS_ABORTED = 1u << 15,
// |COMPACTION_WAS_ABORTED_FOR_TESTING|: During stress testing evacuation
// on pages is sometimes aborted. The flag is used to avoid repeatedly
// triggering on the same page.
COMPACTION_WAS_ABORTED_FOR_TESTING = 1u << 16,
// |SWEEP_TO_ITERATE|: The page requires sweeping using external markbits
// to iterate the page.
SWEEP_TO_ITERATE = 1u << 17,
// |INCREMENTAL_MARKING|: Indicates whether incremental marking is currently
// enabled.
INCREMENTAL_MARKING = 1u << 18,
NEW_SPACE_BELOW_AGE_MARK = 1u << 19,
// The memory chunk freeing bookkeeping has been performed but the chunk has
// not yet been freed.
UNREGISTERED = 1u << 20,
// The memory chunk belongs to the read-only heap and does not participate
// in garbage collection. This is used instead of owner for identity
// checking since read-only chunks have no owner once they are detached.
READ_ONLY_HEAP = 1u << 21,
// The memory chunk is pinned in memory and can't be moved. This is likely
// because there exists a potential pointer to somewhere in the chunk which
// can't be updated.
PINNED = 1u << 22,
};
static const intptr_t kAlignment =
(static_cast<uintptr_t>(1) << kPageSizeBits);
static const intptr_t kAlignmentMask = kAlignment - 1;
BasicMemoryChunk(size_t size, Address area_start, Address area_end);
static Address BaseAddress(Address a) { return a & ~kAlignmentMask; }
Address address() const { return reinterpret_cast<Address>(this); }
// Returns the offset of a given address to this page.
inline size_t Offset(Address a) { return static_cast<size_t>(a - address()); }
// Some callers rely on the fact that this can operate on both
// tagged and aligned object addresses.
inline uint32_t AddressToMarkbitIndex(Address addr) const {
return static_cast<uint32_t>(addr - this->address()) >> kTaggedSizeLog2;
}
inline Address MarkbitIndexToAddress(uint32_t index) const {
return this->address() + (index << kTaggedSizeLog2);
}
size_t size() const { return size_; }
void set_size(size_t size) { size_ = size; }
Address area_start() const { return area_start_; }
Address area_end() const { return area_end_; }
void set_area_end(Address area_end) { area_end_ = area_end; }
size_t area_size() const {
return static_cast<size_t>(area_end() - area_start());
}
Heap* heap() const {
DCHECK_NOT_NULL(heap_);
return heap_;
}
// Gets the chunk's owner or null if the space has been detached.
BaseSpace* owner() const { return owner_; }
void set_owner(BaseSpace* space) { owner_ = space; }
template <AccessMode access_mode = AccessMode::NON_ATOMIC>
void SetFlag(Flag flag) {
if (access_mode == AccessMode::NON_ATOMIC) {
flags_ |= flag;
} else {
base::AsAtomicWord::SetBits<uintptr_t>(&flags_, flag, flag);
}
}
template <AccessMode access_mode = AccessMode::NON_ATOMIC>
bool IsFlagSet(Flag flag) const {
return (GetFlags<access_mode>() & flag) != 0;
}
void ClearFlag(Flag flag) { flags_ &= ~flag; }
// Set or clear multiple flags at a time. The flags in the mask are set to
// the value in "flags", the rest retain the current value in |flags_|.
void SetFlags(uintptr_t flags, uintptr_t mask) {
flags_ = (flags_ & ~mask) | (flags & mask);
}
// Return all current flags.
template <AccessMode access_mode = AccessMode::NON_ATOMIC>
uintptr_t GetFlags() const {
if (access_mode == AccessMode::NON_ATOMIC) {
return flags_;
} else {
return base::AsAtomicWord::Relaxed_Load(&flags_);
}
}
using Flags = uintptr_t;
static const Flags kPointersToHereAreInterestingMask =
POINTERS_TO_HERE_ARE_INTERESTING;
static const Flags kPointersFromHereAreInterestingMask =
POINTERS_FROM_HERE_ARE_INTERESTING;
static const Flags kEvacuationCandidateMask = EVACUATION_CANDIDATE;
static const Flags kIsInYoungGenerationMask = FROM_PAGE | TO_PAGE;
static const Flags kIsLargePageMask = LARGE_PAGE;
static const Flags kSkipEvacuationSlotsRecordingMask =
kEvacuationCandidateMask | kIsInYoungGenerationMask;
private:
bool InReadOnlySpaceRaw() const { return IsFlagSet(READ_ONLY_HEAP); }
public:
bool InReadOnlySpace() const {
#ifdef THREAD_SANITIZER
// This is needed because TSAN does not process the memory fence
// emitted after page initialization.
SynchronizedHeapLoad();
#endif
return IsFlagSet(READ_ONLY_HEAP);
}
bool NeverEvacuate() { return IsFlagSet(NEVER_EVACUATE); }
void MarkNeverEvacuate() { SetFlag(NEVER_EVACUATE); }
bool CanAllocate() {
return !IsEvacuationCandidate() && !IsFlagSet(NEVER_ALLOCATE_ON_PAGE);
}
template <AccessMode access_mode = AccessMode::NON_ATOMIC>
bool IsEvacuationCandidate() {
DCHECK(!(IsFlagSet<access_mode>(NEVER_EVACUATE) &&
IsFlagSet<access_mode>(EVACUATION_CANDIDATE)));
return IsFlagSet<access_mode>(EVACUATION_CANDIDATE);
}
template <AccessMode access_mode = AccessMode::NON_ATOMIC>
bool ShouldSkipEvacuationSlotRecording() {
uintptr_t flags = GetFlags<access_mode>();
return ((flags & kSkipEvacuationSlotsRecordingMask) != 0) &&
((flags & COMPACTION_WAS_ABORTED) == 0);
}
Executability executable() {
return IsFlagSet(IS_EXECUTABLE) ? EXECUTABLE : NOT_EXECUTABLE;
}
bool IsFromPage() const { return IsFlagSet(FROM_PAGE); }
bool IsToPage() const { return IsFlagSet(TO_PAGE); }
bool IsLargePage() const { return IsFlagSet(LARGE_PAGE); }
bool InYoungGeneration() const {
return (GetFlags() & kIsInYoungGenerationMask) != 0;
}
bool InNewSpace() const { return InYoungGeneration() && !IsLargePage(); }
bool InNewLargeObjectSpace() const {
return InYoungGeneration() && IsLargePage();
}
bool InOldSpace() const;
V8_EXPORT_PRIVATE bool InLargeObjectSpace() const;
bool IsWritable() const {
// If this is a read-only space chunk but heap_ is non-null, it has not yet
// been sealed and can be written to.
return !InReadOnlySpace() || heap_ != nullptr;
}
bool IsPinned() const { return IsFlagSet(PINNED); }
bool Contains(Address addr) const {
return addr >= area_start() && addr < area_end();
}
// Checks whether |addr| can be a limit of addresses in this page. It's a
// limit if it's in the page, or if it's just after the last byte of the page.
bool ContainsLimit(Address addr) const {
return addr >= area_start() && addr <= area_end();
}
static BasicMemoryChunk* Initialize(Heap* heap, Address base, size_t size,
Address area_start, Address area_end,
BaseSpace* owner,
VirtualMemory reservation);
size_t wasted_memory() const { return wasted_memory_; }
void add_wasted_memory(size_t waste) { wasted_memory_ += waste; }
size_t allocated_bytes() const { return allocated_bytes_; }
static const intptr_t kSizeOffset = MemoryChunkLayout::kSizeOffset;
static const intptr_t kFlagsOffset = MemoryChunkLayout::kFlagsOffset;
static const intptr_t kHeapOffset = MemoryChunkLayout::kHeapOffset;
static const intptr_t kAreaStartOffset = MemoryChunkLayout::kAreaStartOffset;
static const intptr_t kAreaEndOffset = MemoryChunkLayout::kAreaEndOffset;
static const intptr_t kMarkingBitmapOffset =
MemoryChunkLayout::kMarkingBitmapOffset;
static const size_t kHeaderSize =
MemoryChunkLayout::kBasicMemoryChunkHeaderSize;
// Only works if the pointer is in the first kPageSize of the MemoryChunk.
static BasicMemoryChunk* FromAddress(Address a) {
return reinterpret_cast<BasicMemoryChunk*>(BaseAddress(a));
}
// Only works if the object is in the first kPageSize of the MemoryChunk.
static BasicMemoryChunk* FromHeapObject(HeapObject o) {
return reinterpret_cast<BasicMemoryChunk*>(BaseAddress(o.ptr()));
}
template <AccessMode mode>
ConcurrentBitmap<mode>* marking_bitmap() const {
return static_cast<ConcurrentBitmap<mode>*>(
Bitmap::FromAddress(address() + kMarkingBitmapOffset));
}
Address HighWaterMark() { return address() + high_water_mark_; }
static inline void UpdateHighWaterMark(Address mark) {
if (mark == kNullAddress) return;
// Need to subtract one from the mark because when a chunk is full the
// top points to the next address after the chunk, which effectively belongs
// to another chunk. See the comment to Page::FromAllocationAreaAddress.
BasicMemoryChunk* chunk = BasicMemoryChunk::FromAddress(mark - 1);
intptr_t new_mark = static_cast<intptr_t>(mark - chunk->address());
intptr_t old_mark = chunk->high_water_mark_.load(std::memory_order_relaxed);
while ((new_mark > old_mark) &&
!chunk->high_water_mark_.compare_exchange_weak(
old_mark, new_mark, std::memory_order_acq_rel)) {
}
}
VirtualMemory* reserved_memory() { return &reservation_; }
void ResetAllocationStatistics() {
allocated_bytes_ = area_size();
wasted_memory_ = 0;
}
void IncreaseAllocatedBytes(size_t bytes) {
DCHECK_LE(bytes, area_size());
allocated_bytes_ += bytes;
}
void DecreaseAllocatedBytes(size_t bytes) {
DCHECK_LE(bytes, area_size());
DCHECK_GE(allocated_bytes(), bytes);
allocated_bytes_ -= bytes;
}
#ifdef THREAD_SANITIZER
// Perform a dummy acquire load to tell TSAN that there is no data race in
// mark-bit initialization. See MemoryChunk::Initialize for the corresponding
// release store.
void SynchronizedHeapLoad() const;
#endif
protected:
// Overall size of the chunk, including the header and guards.
size_t size_;
uintptr_t flags_ = NO_FLAGS;
// TODO(v8:7464): Find a way to remove this.
// This goes against the spirit for the BasicMemoryChunk, but until C++14/17
// is the default it needs to live here because MemoryChunk is not standard
// layout under C++11.
Heap* heap_;
// Start and end of allocatable memory on this chunk.
Address area_start_;
Address area_end_;
// Byte allocated on the page, which includes all objects on the page and the
// linear allocation area.
size_t allocated_bytes_;
// Freed memory that was not added to the free list.
size_t wasted_memory_;
// Assuming the initial allocation on a page is sequential, count highest
// number of bytes ever allocated on the page.
std::atomic<intptr_t> high_water_mark_;
// The space owning this memory chunk.
std::atomic<BaseSpace*> owner_;
// If the chunk needs to remember its memory reservation, it is stored here.
VirtualMemory reservation_;
friend class BasicMemoryChunkValidator;
friend class ConcurrentMarkingState;
friend class MajorMarkingState;
friend class MajorAtomicMarkingState;
friend class MajorNonAtomicMarkingState;
friend class MemoryAllocator;
friend class MinorMarkingState;
friend class MinorNonAtomicMarkingState;
friend class PagedSpace;
};
STATIC_ASSERT(std::is_standard_layout<BasicMemoryChunk>::value);
} // namespace internal
} // namespace v8
#endif // V8_HEAP_BASIC_MEMORY_CHUNK_H_
|