File: central_freelist.cc

package info (click to toggle)
google-perftools 2.7-1
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, buster, sid
  • size: 7,284 kB
  • sloc: cpp: 27,869; ansic: 9,534; sh: 4,799; perl: 4,116; makefile: 1,101; asm: 128
file content (387 lines) | stat: -rw-r--r-- 12,647 bytes parent folder | download | duplicates (3)
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
// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Sanjay Ghemawat <opensource@google.com>

#include "config.h"
#include <algorithm>
#include "central_freelist.h"
#include "internal_logging.h"  // for ASSERT, MESSAGE
#include "linked_list.h"       // for SLL_Next, SLL_Push, etc
#include "page_heap.h"         // for PageHeap
#include "static_vars.h"       // for Static

using std::min;
using std::max;

namespace tcmalloc {

void CentralFreeList::Init(size_t cl) {
  size_class_ = cl;
  tcmalloc::DLL_Init(&empty_);
  tcmalloc::DLL_Init(&nonempty_);
  num_spans_ = 0;
  counter_ = 0;

  max_cache_size_ = kMaxNumTransferEntries;
#ifdef TCMALLOC_SMALL_BUT_SLOW
  // Disable the transfer cache for the small footprint case.
  cache_size_ = 0;
#else
  cache_size_ = 16;
#endif
  if (cl > 0) {
    // Limit the maximum size of the cache based on the size class.  If this
    // is not done, large size class objects will consume a lot of memory if
    // they just sit in the transfer cache.
    int32_t bytes = Static::sizemap()->ByteSizeForClass(cl);
    int32_t objs_to_move = Static::sizemap()->num_objects_to_move(cl);

    ASSERT(objs_to_move > 0 && bytes > 0);
    // Limit each size class cache to at most 1MB of objects or one entry,
    // whichever is greater. Total transfer cache memory used across all
    // size classes then can't be greater than approximately
    // 1MB * kMaxNumTransferEntries.
    // min and max are in parens to avoid macro-expansion on windows.
    max_cache_size_ = (min)(max_cache_size_,
                          (max)(1, (1024 * 1024) / (bytes * objs_to_move)));
    cache_size_ = (min)(cache_size_, max_cache_size_);
  }
  used_slots_ = 0;
  ASSERT(cache_size_ <= max_cache_size_);
}

void CentralFreeList::ReleaseListToSpans(void* start) {
  while (start) {
    void *next = SLL_Next(start);
    ReleaseToSpans(start);
    start = next;
  }
}

// MapObjectToSpan should logically be part of ReleaseToSpans.  But
// this triggers an optimization bug in gcc 4.5.0.  Moving to a
// separate function, and making sure that function isn't inlined,
// seems to fix the problem.  It also should be fixed for gcc 4.5.1.
static
#if __GNUC__ == 4 && __GNUC_MINOR__ == 5 && __GNUC_PATCHLEVEL__ == 0
__attribute__ ((noinline))
#endif
Span* MapObjectToSpan(void* object) {
  const PageID p = reinterpret_cast<uintptr_t>(object) >> kPageShift;
  Span* span = Static::pageheap()->GetDescriptor(p);
  return span;
}

void CentralFreeList::ReleaseToSpans(void* object) {
  Span* span = MapObjectToSpan(object);
  ASSERT(span != NULL);
  ASSERT(span->refcount > 0);

  // If span is empty, move it to non-empty list
  if (span->objects == NULL) {
    tcmalloc::DLL_Remove(span);
    tcmalloc::DLL_Prepend(&nonempty_, span);
    Event(span, 'N', 0);
  }

  // The following check is expensive, so it is disabled by default
  if (false) {
    // Check that object does not occur in list
    int got = 0;
    for (void* p = span->objects; p != NULL; p = *((void**) p)) {
      ASSERT(p != object);
      got++;
    }
    ASSERT(got + span->refcount ==
           (span->length<<kPageShift) /
           Static::sizemap()->ByteSizeForClass(span->sizeclass));
  }

  counter_++;
  span->refcount--;
  if (span->refcount == 0) {
    Event(span, '#', 0);
    counter_ -= ((span->length<<kPageShift) /
                 Static::sizemap()->ByteSizeForClass(span->sizeclass));
    tcmalloc::DLL_Remove(span);
    --num_spans_;

    // Release central list lock while operating on pageheap
    lock_.Unlock();
    {
      SpinLockHolder h(Static::pageheap_lock());
      Static::pageheap()->Delete(span);
    }
    lock_.Lock();
  } else {
    *(reinterpret_cast<void**>(object)) = span->objects;
    span->objects = object;
  }
}

bool CentralFreeList::EvictRandomSizeClass(
    int locked_size_class, bool force) {
  static int race_counter = 0;
  int t = race_counter++;  // Updated without a lock, but who cares.
  if (t >= Static::num_size_classes()) {
    while (t >= Static::num_size_classes()) {
      t -= Static::num_size_classes();
    }
    race_counter = t;
  }
  ASSERT(t >= 0);
  ASSERT(t < Static::num_size_classes());
  if (t == locked_size_class) return false;
  return Static::central_cache()[t].ShrinkCache(locked_size_class, force);
}

bool CentralFreeList::MakeCacheSpace() {
  // Is there room in the cache?
  if (used_slots_ < cache_size_) return true;
  // Check if we can expand this cache?
  if (cache_size_ == max_cache_size_) return false;
  // Ok, we'll try to grab an entry from some other size class.
  if (EvictRandomSizeClass(size_class_, false) ||
      EvictRandomSizeClass(size_class_, true)) {
    // Succeeded in evicting, we're going to make our cache larger.
    // However, we may have dropped and re-acquired the lock in
    // EvictRandomSizeClass (via ShrinkCache and the LockInverter), so the
    // cache_size may have changed.  Therefore, check and verify that it is
    // still OK to increase the cache_size.
    if (cache_size_ < max_cache_size_) {
      cache_size_++;
      return true;
    }
  }
  return false;
}


namespace {
class LockInverter {
 private:
  SpinLock *held_, *temp_;
 public:
  inline explicit LockInverter(SpinLock* held, SpinLock *temp)
    : held_(held), temp_(temp) { held_->Unlock(); temp_->Lock(); }
  inline ~LockInverter() { temp_->Unlock(); held_->Lock();  }
};
}

// This function is marked as NO_THREAD_SAFETY_ANALYSIS because it uses
// LockInverter to release one lock and acquire another in scoped-lock
// style, which our current annotation/analysis does not support.
bool CentralFreeList::ShrinkCache(int locked_size_class, bool force)
    NO_THREAD_SAFETY_ANALYSIS {
  // Start with a quick check without taking a lock.
  if (cache_size_ == 0) return false;
  // We don't evict from a full cache unless we are 'forcing'.
  if (force == false && used_slots_ == cache_size_) return false;

  // Grab lock, but first release the other lock held by this thread.  We use
  // the lock inverter to ensure that we never hold two size class locks
  // concurrently.  That can create a deadlock because there is no well
  // defined nesting order.
  LockInverter li(&Static::central_cache()[locked_size_class].lock_, &lock_);
  ASSERT(used_slots_ <= cache_size_);
  ASSERT(0 <= cache_size_);
  if (cache_size_ == 0) return false;
  if (used_slots_ == cache_size_) {
    if (force == false) return false;
    // ReleaseListToSpans releases the lock, so we have to make all the
    // updates to the central list before calling it.
    cache_size_--;
    used_slots_--;
    ReleaseListToSpans(tc_slots_[used_slots_].head);
    return true;
  }
  cache_size_--;
  return true;
}

void CentralFreeList::InsertRange(void *start, void *end, int N) {
  SpinLockHolder h(&lock_);
  if (N == Static::sizemap()->num_objects_to_move(size_class_) &&
    MakeCacheSpace()) {
    int slot = used_slots_++;
    ASSERT(slot >=0);
    ASSERT(slot < max_cache_size_);
    TCEntry *entry = &tc_slots_[slot];
    entry->head = start;
    entry->tail = end;
    return;
  }
  ReleaseListToSpans(start);
}

int CentralFreeList::RemoveRange(void **start, void **end, int N) {
  ASSERT(N > 0);
  lock_.Lock();
  if (N == Static::sizemap()->num_objects_to_move(size_class_) &&
      used_slots_ > 0) {
    int slot = --used_slots_;
    ASSERT(slot >= 0);
    TCEntry *entry = &tc_slots_[slot];
    *start = entry->head;
    *end = entry->tail;
    lock_.Unlock();
    return N;
  }

  int result = 0;
  *start = NULL;
  *end = NULL;
  // TODO: Prefetch multiple TCEntries?
  result = FetchFromOneSpansSafe(N, start, end);
  if (result != 0) {
    while (result < N) {
      int n;
      void* head = NULL;
      void* tail = NULL;
      n = FetchFromOneSpans(N - result, &head, &tail);
      if (!n) break;
      result += n;
      SLL_PushRange(start, head, tail);
    }
  }
  lock_.Unlock();
  return result;
}


int CentralFreeList::FetchFromOneSpansSafe(int N, void **start, void **end) {
  int result = FetchFromOneSpans(N, start, end);
  if (!result) {
    Populate();
    result = FetchFromOneSpans(N, start, end);
  }
  return result;
}

int CentralFreeList::FetchFromOneSpans(int N, void **start, void **end) {
  if (tcmalloc::DLL_IsEmpty(&nonempty_)) return 0;
  Span* span = nonempty_.next;

  ASSERT(span->objects != NULL);

  int result = 0;
  void *prev, *curr;
  curr = span->objects;
  do {
    prev = curr;
    curr = *(reinterpret_cast<void**>(curr));
  } while (++result < N && curr != NULL);

  if (curr == NULL) {
    // Move to empty list
    tcmalloc::DLL_Remove(span);
    tcmalloc::DLL_Prepend(&empty_, span);
    Event(span, 'E', 0);
  }

  *start = span->objects;
  *end = prev;
  span->objects = curr;
  SLL_SetNext(*end, NULL);
  span->refcount += result;
  counter_ -= result;
  return result;
}

// Fetch memory from the system and add to the central cache freelist.
void CentralFreeList::Populate() {
  // Release central list lock while operating on pageheap
  lock_.Unlock();
  const size_t npages = Static::sizemap()->class_to_pages(size_class_);

  Span* span;
  {
    SpinLockHolder h(Static::pageheap_lock());
    span = Static::pageheap()->New(npages);
    if (span) Static::pageheap()->RegisterSizeClass(span, size_class_);
  }
  if (span == NULL) {
    Log(kLog, __FILE__, __LINE__,
        "tcmalloc: allocation failed", npages << kPageShift);
    lock_.Lock();
    return;
  }
  ASSERT(span->length == npages);
  // Cache sizeclass info eagerly.  Locking is not necessary.
  // (Instead of being eager, we could just replace any stale info
  // about this span, but that seems to be no better in practice.)
  for (int i = 0; i < npages; i++) {
    Static::pageheap()->SetCachedSizeClass(span->start + i, size_class_);
  }

  // Split the block into pieces and add to the free-list
  // TODO: coloring of objects to avoid cache conflicts?
  void** tail = &span->objects;
  char* ptr = reinterpret_cast<char*>(span->start << kPageShift);
  char* limit = ptr + (npages << kPageShift);
  const size_t size = Static::sizemap()->ByteSizeForClass(size_class_);
  int num = 0;
  while (ptr + size <= limit) {
    *tail = ptr;
    tail = reinterpret_cast<void**>(ptr);
    ptr += size;
    num++;
  }
  ASSERT(ptr <= limit);
  *tail = NULL;
  span->refcount = 0; // No sub-object in use yet

  // Add span to list of non-empty spans
  lock_.Lock();
  tcmalloc::DLL_Prepend(&nonempty_, span);
  ++num_spans_;
  counter_ += num;
}

int CentralFreeList::tc_length() {
  SpinLockHolder h(&lock_);
  return used_slots_ * Static::sizemap()->num_objects_to_move(size_class_);
}

size_t CentralFreeList::OverheadBytes() {
  SpinLockHolder h(&lock_);
  if (size_class_ == 0) {  // 0 holds the 0-sized allocations
    return 0;
  }
  const size_t pages_per_span = Static::sizemap()->class_to_pages(size_class_);
  const size_t object_size = Static::sizemap()->class_to_size(size_class_);
  ASSERT(object_size > 0);
  const size_t overhead_per_span = (pages_per_span * kPageSize) % object_size;
  return num_spans_ * overhead_per_span;
}

}  // namespace tcmalloc