forked from chromium/chromium
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathdiscardable_shared_memory.cc
442 lines (368 loc) · 14.9 KB
/
discardable_shared_memory.cc
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
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/memory/discardable_shared_memory.h"
#include <stdint.h>
#include <algorithm>
#include "base/atomicops.h"
#include "base/bits.h"
#include "base/logging.h"
#include "base/numerics/safe_math.h"
#include "base/process/process_metrics.h"
#include "build/build_config.h"
#if defined(OS_POSIX) && !defined(OS_NACL)
// For madvise() which is available on all POSIX compatible systems.
#include <sys/mman.h>
#endif
#if defined(OS_ANDROID)
#include "third_party/ashmem/ashmem.h"
#endif
#if defined(OS_WIN)
#include "base/win/windows_version.h"
#endif
namespace base {
namespace {
// Use a machine-sized pointer as atomic type. It will use the Atomic32 or
// Atomic64 routines, depending on the architecture.
typedef intptr_t AtomicType;
typedef uintptr_t UAtomicType;
// Template specialization for timestamp serialization/deserialization. This
// is used to serialize timestamps using Unix time on systems where AtomicType
// does not have enough precision to contain a timestamp in the standard
// serialized format.
template <int>
Time TimeFromWireFormat(int64_t value);
template <int>
int64_t TimeToWireFormat(Time time);
// Serialize to Unix time when using 4-byte wire format.
// Note: 19 January 2038, this will cease to work.
template <>
Time ALLOW_UNUSED_TYPE TimeFromWireFormat<4>(int64_t value) {
return value ? Time::UnixEpoch() + TimeDelta::FromSeconds(value) : Time();
}
template <>
int64_t ALLOW_UNUSED_TYPE TimeToWireFormat<4>(Time time) {
return time > Time::UnixEpoch() ? (time - Time::UnixEpoch()).InSeconds() : 0;
}
// Standard serialization format when using 8-byte wire format.
template <>
Time ALLOW_UNUSED_TYPE TimeFromWireFormat<8>(int64_t value) {
return Time::FromInternalValue(value);
}
template <>
int64_t ALLOW_UNUSED_TYPE TimeToWireFormat<8>(Time time) {
return time.ToInternalValue();
}
struct SharedState {
enum LockState { UNLOCKED = 0, LOCKED = 1 };
explicit SharedState(AtomicType ivalue) { value.i = ivalue; }
SharedState(LockState lock_state, Time timestamp) {
int64_t wire_timestamp = TimeToWireFormat<sizeof(AtomicType)>(timestamp);
DCHECK_GE(wire_timestamp, 0);
DCHECK_EQ(lock_state & ~1, 0);
value.u = (static_cast<UAtomicType>(wire_timestamp) << 1) | lock_state;
}
LockState GetLockState() const { return static_cast<LockState>(value.u & 1); }
Time GetTimestamp() const {
return TimeFromWireFormat<sizeof(AtomicType)>(value.u >> 1);
}
// Bit 1: Lock state. Bit is set when locked.
// Bit 2..sizeof(AtomicType)*8: Usage timestamp. NULL time when locked or
// purged.
union {
AtomicType i;
UAtomicType u;
} value;
};
// Shared state is stored at offset 0 in shared memory segments.
SharedState* SharedStateFromSharedMemory(const SharedMemory& shared_memory) {
DCHECK(shared_memory.memory());
return static_cast<SharedState*>(shared_memory.memory());
}
// Round up |size| to a multiple of page size.
size_t AlignToPageSize(size_t size) {
return bits::Align(size, base::GetPageSize());
}
// LockPages/UnlockPages are platform-native discardable page management
// helper functions. Both expect |offset| to be specified relative to the
// base address at which |memory| is mapped, and that |offset| and |length|
// are page-aligned by the caller.
// Returns SUCCESS on platforms which do not support discardable pages.
DiscardableSharedMemory::LockResult LockPages(const SharedMemory& memory,
size_t offset,
size_t length) {
#if defined(OS_ANDROID)
SharedMemoryHandle handle = memory.handle();
if (handle.IsValid()) {
int pin_result = ashmem_pin_region(handle.GetHandle(), offset, length);
if (pin_result == ASHMEM_WAS_PURGED)
return DiscardableSharedMemory::PURGED;
if (pin_result < 0)
return DiscardableSharedMemory::FAILED;
}
#endif
return DiscardableSharedMemory::SUCCESS;
}
// UnlockPages() is a no-op on platforms not supporting discardable pages.
void UnlockPages(const SharedMemory& memory, size_t offset, size_t length) {
#if defined(OS_ANDROID)
SharedMemoryHandle handle = memory.handle();
if (handle.IsValid()) {
int unpin_result = ashmem_unpin_region(handle.GetHandle(), offset, length);
DCHECK_EQ(0, unpin_result);
}
#endif
}
} // namespace
DiscardableSharedMemory::DiscardableSharedMemory()
: mapped_size_(0), locked_page_count_(0) {
}
DiscardableSharedMemory::DiscardableSharedMemory(
SharedMemoryHandle shared_memory_handle)
: shared_memory_(shared_memory_handle, false),
mapped_size_(0),
locked_page_count_(0) {
}
DiscardableSharedMemory::~DiscardableSharedMemory() {
}
bool DiscardableSharedMemory::CreateAndMap(size_t size) {
CheckedNumeric<size_t> checked_size = size;
checked_size += AlignToPageSize(sizeof(SharedState));
if (!checked_size.IsValid())
return false;
if (!shared_memory_.CreateAndMapAnonymous(checked_size.ValueOrDie()))
return false;
mapped_size_ =
shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
#if DCHECK_IS_ON()
for (size_t page = 0; page < locked_page_count_; ++page)
locked_pages_.insert(page);
#endif
DCHECK(last_known_usage_.is_null());
SharedState new_state(SharedState::LOCKED, Time());
subtle::Release_Store(&SharedStateFromSharedMemory(shared_memory_)->value.i,
new_state.value.i);
return true;
}
bool DiscardableSharedMemory::Map(size_t size) {
if (!shared_memory_.Map(AlignToPageSize(sizeof(SharedState)) + size))
return false;
mapped_size_ =
shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
#if DCHECK_IS_ON()
for (size_t page = 0; page < locked_page_count_; ++page)
locked_pages_.insert(page);
#endif
return true;
}
bool DiscardableSharedMemory::Unmap() {
if (!shared_memory_.Unmap())
return false;
locked_page_count_ = 0;
#if DCHECK_IS_ON()
locked_pages_.clear();
#endif
mapped_size_ = 0;
return true;
}
DiscardableSharedMemory::LockResult DiscardableSharedMemory::Lock(
size_t offset, size_t length) {
DCHECK_EQ(AlignToPageSize(offset), offset);
DCHECK_EQ(AlignToPageSize(length), length);
// Calls to this function must be synchronized properly.
DFAKE_SCOPED_LOCK(thread_collision_warner_);
DCHECK(shared_memory_.memory());
// We need to successfully acquire the platform independent lock before
// individual pages can be locked.
if (!locked_page_count_) {
// Return false when instance has been purged or not initialized properly
// by checking if |last_known_usage_| is NULL.
if (last_known_usage_.is_null())
return FAILED;
SharedState old_state(SharedState::UNLOCKED, last_known_usage_);
SharedState new_state(SharedState::LOCKED, Time());
SharedState result(subtle::Acquire_CompareAndSwap(
&SharedStateFromSharedMemory(shared_memory_)->value.i,
old_state.value.i,
new_state.value.i));
if (result.value.u != old_state.value.u) {
// Update |last_known_usage_| in case the above CAS failed because of
// an incorrect timestamp.
last_known_usage_ = result.GetTimestamp();
return FAILED;
}
}
// Zero for length means "everything onward".
if (!length)
length = AlignToPageSize(mapped_size_) - offset;
size_t start = offset / base::GetPageSize();
size_t end = start + length / base::GetPageSize();
DCHECK_LE(start, end);
DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
// Add pages to |locked_page_count_|.
// Note: Locking a page that is already locked is an error.
locked_page_count_ += end - start;
#if DCHECK_IS_ON()
// Detect incorrect usage by keeping track of exactly what pages are locked.
for (auto page = start; page < end; ++page) {
auto result = locked_pages_.insert(page);
DCHECK(result.second);
}
DCHECK_EQ(locked_pages_.size(), locked_page_count_);
#endif
// Always behave as if memory was purged when trying to lock a 0 byte segment.
if (!length)
return PURGED;
// Ensure that the platform won't discard the required pages.
return LockPages(shared_memory_,
AlignToPageSize(sizeof(SharedState)) + offset, length);
}
void DiscardableSharedMemory::Unlock(size_t offset, size_t length) {
DCHECK_EQ(AlignToPageSize(offset), offset);
DCHECK_EQ(AlignToPageSize(length), length);
// Calls to this function must be synchronized properly.
DFAKE_SCOPED_LOCK(thread_collision_warner_);
// Passing zero for |length| means "everything onward". Note that |length| may
// still be zero after this calculation, e.g. if |mapped_size_| is zero.
if (!length)
length = AlignToPageSize(mapped_size_) - offset;
DCHECK(shared_memory_.memory());
// Allow the pages to be discarded by the platform, if supported.
UnlockPages(shared_memory_, AlignToPageSize(sizeof(SharedState)) + offset,
length);
size_t start = offset / base::GetPageSize();
size_t end = start + length / base::GetPageSize();
DCHECK_LE(start, end);
DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
// Remove pages from |locked_page_count_|.
// Note: Unlocking a page that is not locked is an error.
DCHECK_GE(locked_page_count_, end - start);
locked_page_count_ -= end - start;
#if DCHECK_IS_ON()
// Detect incorrect usage by keeping track of exactly what pages are locked.
for (auto page = start; page < end; ++page) {
auto erased_count = locked_pages_.erase(page);
DCHECK_EQ(1u, erased_count);
}
DCHECK_EQ(locked_pages_.size(), locked_page_count_);
#endif
// Early out and avoid releasing the platform independent lock if some pages
// are still locked.
if (locked_page_count_)
return;
Time current_time = Now();
DCHECK(!current_time.is_null());
SharedState old_state(SharedState::LOCKED, Time());
SharedState new_state(SharedState::UNLOCKED, current_time);
// Note: timestamp cannot be NULL as that is a unique value used when
// locked or purged.
DCHECK(!new_state.GetTimestamp().is_null());
// Timestamp precision should at least be accurate to the second.
DCHECK_EQ((new_state.GetTimestamp() - Time::UnixEpoch()).InSeconds(),
(current_time - Time::UnixEpoch()).InSeconds());
SharedState result(subtle::Release_CompareAndSwap(
&SharedStateFromSharedMemory(shared_memory_)->value.i,
old_state.value.i,
new_state.value.i));
DCHECK_EQ(old_state.value.u, result.value.u);
last_known_usage_ = current_time;
}
void* DiscardableSharedMemory::memory() const {
return reinterpret_cast<uint8_t*>(shared_memory_.memory()) +
AlignToPageSize(sizeof(SharedState));
}
bool DiscardableSharedMemory::Purge(Time current_time) {
// Calls to this function must be synchronized properly.
DFAKE_SCOPED_LOCK(thread_collision_warner_);
DCHECK(shared_memory_.memory());
SharedState old_state(SharedState::UNLOCKED, last_known_usage_);
SharedState new_state(SharedState::UNLOCKED, Time());
SharedState result(subtle::Acquire_CompareAndSwap(
&SharedStateFromSharedMemory(shared_memory_)->value.i,
old_state.value.i,
new_state.value.i));
// Update |last_known_usage_| to |current_time| if the memory is locked. This
// allows the caller to determine if purging failed because last known usage
// was incorrect or memory was locked. In the second case, the caller should
// most likely wait for some amount of time before attempting to purge the
// the memory again.
if (result.value.u != old_state.value.u) {
last_known_usage_ = result.GetLockState() == SharedState::LOCKED
? current_time
: result.GetTimestamp();
return false;
}
// The next section will release as much resource as can be done
// from the purging process, until the client process notices the
// purge and releases its own references.
// Note: this memory will not be accessed again. The segment will be
// freed asynchronously at a later time, so just do the best
// immediately.
#if defined(OS_POSIX) && !defined(OS_NACL)
// Linux and Android provide MADV_REMOVE which is preferred as it has a
// behavior that can be verified in tests. Other POSIX flavors (MacOSX, BSDs),
// provide MADV_FREE which has the same result but memory is purged lazily.
#if defined(OS_LINUX) || defined(OS_ANDROID)
#define MADV_PURGE_ARGUMENT MADV_REMOVE
#elif defined(OS_MACOSX)
// MADV_FREE_REUSABLE is similar to MADV_FREE, but also marks the pages with the
// reusable bit, which allows both Activity Monitor and memory-infra to
// correctly track the pages.
#define MADV_PURGE_ARGUMENT MADV_FREE_REUSABLE
#else
#define MADV_PURGE_ARGUMENT MADV_FREE
#endif
// Advise the kernel to remove resources associated with purged pages.
// Subsequent accesses of memory pages will succeed, but might result in
// zero-fill-on-demand pages.
if (madvise(reinterpret_cast<char*>(shared_memory_.memory()) +
AlignToPageSize(sizeof(SharedState)),
AlignToPageSize(mapped_size_), MADV_PURGE_ARGUMENT)) {
DPLOG(ERROR) << "madvise() failed";
}
#elif defined(OS_WIN)
if (base::win::GetVersion() >= base::win::VERSION_WIN8_1) {
// Discard the purged pages, which releases the physical storage (resident
// memory, compressed or swapped), but leaves them reserved & committed.
// This does not free commit for use by other applications, but allows the
// system to avoid compressing/swapping these pages to free physical memory.
static const auto discard_virtual_memory =
reinterpret_cast<decltype(&::DiscardVirtualMemory)>(GetProcAddress(
GetModuleHandle(L"kernel32.dll"), "DiscardVirtualMemory"));
if (discard_virtual_memory) {
DWORD discard_result = discard_virtual_memory(
reinterpret_cast<char*>(shared_memory_.memory()) +
AlignToPageSize(sizeof(SharedState)),
AlignToPageSize(mapped_size_));
if (discard_result != ERROR_SUCCESS) {
DLOG(FATAL) << "DiscardVirtualMemory() failed in Purge(): "
<< logging::SystemErrorCodeToString(discard_result);
}
}
}
#endif
last_known_usage_ = Time();
return true;
}
bool DiscardableSharedMemory::IsMemoryResident() const {
DCHECK(shared_memory_.memory());
SharedState result(subtle::NoBarrier_Load(
&SharedStateFromSharedMemory(shared_memory_)->value.i));
return result.GetLockState() == SharedState::LOCKED ||
!result.GetTimestamp().is_null();
}
bool DiscardableSharedMemory::IsMemoryLocked() const {
DCHECK(shared_memory_.memory());
SharedState result(subtle::NoBarrier_Load(
&SharedStateFromSharedMemory(shared_memory_)->value.i));
return result.GetLockState() == SharedState::LOCKED;
}
void DiscardableSharedMemory::Close() {
shared_memory_.Close();
}
Time DiscardableSharedMemory::Now() const {
return Time::Now();
}
} // namespace base