1// Copyright (c) 2008, Google Inc.
2// All rights reserved.
3//
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7//
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9// notice, this list of conditions and the following disclaimer.
10//     * Redistributions in binary form must reproduce the above
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12// in the documentation and/or other materials provided with the
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17//
18// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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22// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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24// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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28// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29
30// ---
31// Author: Sanjay Ghemawat <opensource@google.com>
32
33#include "config.h"
34#include <algorithm>
35#include "central_freelist.h"
36#include "free_list.h"         // for FL_Next, FL_Push, etc
37#include "internal_logging.h"  // for ASSERT, MESSAGE
38#include "page_heap.h"         // for PageHeap
39#include "static_vars.h"       // for Static
40
41using std::min;
42using std::max;
43
44namespace tcmalloc {
45
46void CentralFreeList::Init(size_t cl) {
47  size_class_ = cl;
48  tcmalloc::DLL_Init(&empty_);
49  tcmalloc::DLL_Init(&nonempty_);
50  num_spans_ = 0;
51  counter_ = 0;
52
53  max_cache_size_ = kMaxNumTransferEntries;
54#ifdef TCMALLOC_SMALL_BUT_SLOW
55  // Disable the transfer cache for the small footprint case.
56  cache_size_ = 0;
57#else
58  cache_size_ = 16;
59#endif
60  if (cl > 0) {
61    // Limit the maximum size of the cache based on the size class.  If this
62    // is not done, large size class objects will consume a lot of memory if
63    // they just sit in the transfer cache.
64    int32_t bytes = Static::sizemap()->ByteSizeForClass(cl);
65    int32_t objs_to_move = Static::sizemap()->num_objects_to_move(cl);
66
67    ASSERT(objs_to_move > 0 && bytes > 0);
68    // Limit each size class cache to at most 1MB of objects or one entry,
69    // whichever is greater. Total transfer cache memory used across all
70    // size classes then can't be greater than approximately
71    // 1MB * kMaxNumTransferEntries.
72    // min and max are in parens to avoid macro-expansion on windows.
73    max_cache_size_ = (min)(max_cache_size_,
74                          (max)(1, (1024 * 1024) / (bytes * objs_to_move)));
75    cache_size_ = (min)(cache_size_, max_cache_size_);
76  }
77  used_slots_ = 0;
78  ASSERT(cache_size_ <= max_cache_size_);
79}
80
81void CentralFreeList::ReleaseListToSpans(void* start) {
82  while (start) {
83    void *next = FL_Next(start);
84    ReleaseToSpans(start);
85    start = next;
86  }
87}
88
89// MapObjectToSpan should logically be part of ReleaseToSpans.  But
90// this triggers an optimization bug in gcc 4.5.0.  Moving to a
91// separate function, and making sure that function isn't inlined,
92// seems to fix the problem.  It also should be fixed for gcc 4.5.1.
93static
94#if __GNUC__ == 4 && __GNUC_MINOR__ == 5 && __GNUC_PATCHLEVEL__ == 0
95__attribute__ ((noinline))
96#endif
97Span* MapObjectToSpan(void* object) {
98  const PageID p = reinterpret_cast<uintptr_t>(object) >> kPageShift;
99  Span* span = Static::pageheap()->GetDescriptor(p);
100  return span;
101}
102
103void CentralFreeList::ReleaseToSpans(void* object) {
104  Span* span = MapObjectToSpan(object);
105  ASSERT(span != NULL);
106  ASSERT(span->refcount > 0);
107
108  // If span is empty, move it to non-empty list
109  if (span->objects == NULL) {
110    tcmalloc::DLL_Remove(span);
111    tcmalloc::DLL_Prepend(&nonempty_, span);
112    Event(span, 'N', 0);
113  }
114
115  // The following check is expensive, so it is disabled by default
116  if (false) {
117    // Check that object does not occur in list
118    int got = 0;
119    for (void* p = span->objects; p != NULL; p = FL_Next(p)){
120      ASSERT(p != object);
121      got++;
122    }
123    ASSERT(got + span->refcount ==
124           (span->length<<kPageShift) /
125           Static::sizemap()->ByteSizeForClass(span->sizeclass));
126  }
127
128  counter_++;
129  span->refcount--;
130  if (span->refcount == 0) {
131    Event(span, '#', 0);
132    counter_ -= ((span->length<<kPageShift) /
133                 Static::sizemap()->ByteSizeForClass(span->sizeclass));
134    tcmalloc::DLL_Remove(span);
135    --num_spans_;
136
137    // Release central list lock while operating on pageheap
138    lock_.Unlock();
139    {
140      SpinLockHolder h(Static::pageheap_lock());
141      Static::pageheap()->Delete(span);
142    }
143    lock_.Lock();
144  } else {
145    FL_Push(&(span->objects), object);
146  }
147}
148
149bool CentralFreeList::EvictRandomSizeClass(
150    int locked_size_class, bool force) {
151  static int race_counter = 0;
152  int t = race_counter++;  // Updated without a lock, but who cares.
153  if (t >= kNumClasses) {
154    while (t >= kNumClasses) {
155      t -= kNumClasses;
156    }
157    race_counter = t;
158  }
159  ASSERT(t >= 0);
160  ASSERT(t < kNumClasses);
161  if (t == locked_size_class) return false;
162  return Static::central_cache()[t].ShrinkCache(locked_size_class, force);
163}
164
165bool CentralFreeList::MakeCacheSpace() {
166  // Is there room in the cache?
167  if (used_slots_ < cache_size_) return true;
168  // Check if we can expand this cache?
169  if (cache_size_ == max_cache_size_) return false;
170  // Ok, we'll try to grab an entry from some other size class.
171  if (EvictRandomSizeClass(size_class_, false) ||
172      EvictRandomSizeClass(size_class_, true)) {
173    // Succeeded in evicting, we're going to make our cache larger.
174    // However, we may have dropped and re-acquired the lock in
175    // EvictRandomSizeClass (via ShrinkCache and the LockInverter), so the
176    // cache_size may have changed.  Therefore, check and verify that it is
177    // still OK to increase the cache_size.
178    if (cache_size_ < max_cache_size_) {
179      cache_size_++;
180      return true;
181    }
182  }
183  return false;
184}
185
186
187namespace {
188class LockInverter {
189 private:
190  SpinLock *held_, *temp_;
191 public:
192  inline explicit LockInverter(SpinLock* held, SpinLock *temp)
193    : held_(held), temp_(temp) { held_->Unlock(); temp_->Lock(); }
194  inline ~LockInverter() { temp_->Unlock(); held_->Lock();  }
195};
196}
197
198// This function is marked as NO_THREAD_SAFETY_ANALYSIS because it uses
199// LockInverter to release one lock and acquire another in scoped-lock
200// style, which our current annotation/analysis does not support.
201bool CentralFreeList::ShrinkCache(int locked_size_class, bool force)
202    NO_THREAD_SAFETY_ANALYSIS {
203  // Start with a quick check without taking a lock.
204  if (cache_size_ == 0) return false;
205  // We don't evict from a full cache unless we are 'forcing'.
206  if (force == false && used_slots_ == cache_size_) return false;
207
208  // Grab lock, but first release the other lock held by this thread.  We use
209  // the lock inverter to ensure that we never hold two size class locks
210  // concurrently.  That can create a deadlock because there is no well
211  // defined nesting order.
212  LockInverter li(&Static::central_cache()[locked_size_class].lock_, &lock_);
213  ASSERT(used_slots_ <= cache_size_);
214  ASSERT(0 <= cache_size_);
215  if (cache_size_ == 0) return false;
216  if (used_slots_ == cache_size_) {
217    if (force == false) return false;
218    // ReleaseListToSpans releases the lock, so we have to make all the
219    // updates to the central list before calling it.
220    cache_size_--;
221    used_slots_--;
222    ReleaseListToSpans(tc_slots_[used_slots_].head);
223    return true;
224  }
225  cache_size_--;
226  return true;
227}
228
229void CentralFreeList::InsertRange(void *start, void *end, int N) {
230  SpinLockHolder h(&lock_);
231  if (N == Static::sizemap()->num_objects_to_move(size_class_) &&
232    MakeCacheSpace()) {
233    int slot = used_slots_++;
234    ASSERT(slot >=0);
235    ASSERT(slot < max_cache_size_);
236    TCEntry *entry = &tc_slots_[slot];
237    entry->head = start;
238    entry->tail = end;
239    return;
240  }
241  ReleaseListToSpans(start);
242}
243
244int CentralFreeList::RemoveRange(void **start, void **end, int N) {
245  ASSERT(N > 0);
246  lock_.Lock();
247  if (N == Static::sizemap()->num_objects_to_move(size_class_) &&
248      used_slots_ > 0) {
249    int slot = --used_slots_;
250    ASSERT(slot >= 0);
251    TCEntry *entry = &tc_slots_[slot];
252    *start = entry->head;
253    *end = entry->tail;
254    lock_.Unlock();
255    return N;
256  }
257
258  int result = 0;
259  void* head = NULL;
260  void* tail = NULL;
261  // TODO: Prefetch multiple TCEntries?
262  tail = FetchFromSpansSafe();
263  if (tail != NULL) {
264    FL_Push(&head, tail);
265    result = 1;
266    while (result < N) {
267      void *t = FetchFromSpans();
268      if (!t) break;
269      FL_Push(&head, t);
270      result++;
271    }
272  }
273  lock_.Unlock();
274  *start = head;
275  *end = tail;
276  return result;
277}
278
279
280void* CentralFreeList::FetchFromSpansSafe() {
281  void *t = FetchFromSpans();
282  if (!t) {
283    Populate();
284    t = FetchFromSpans();
285  }
286  return t;
287}
288
289void* CentralFreeList::FetchFromSpans() {
290  if (tcmalloc::DLL_IsEmpty(&nonempty_)) return NULL;
291  Span* span = nonempty_.next;
292
293  ASSERT(span->objects != NULL);
294  span->refcount++;
295  void *result = FL_Pop(&(span->objects));
296  if (span->objects == NULL) {
297    // Move to empty list
298    tcmalloc::DLL_Remove(span);
299    tcmalloc::DLL_Prepend(&empty_, span);
300    Event(span, 'E', 0);
301  }
302  counter_--;
303  return result;
304}
305
306// Fetch memory from the system and add to the central cache freelist.
307void CentralFreeList::Populate() {
308  // Release central list lock while operating on pageheap
309  lock_.Unlock();
310  const size_t npages = Static::sizemap()->class_to_pages(size_class_);
311
312  Span* span;
313  {
314    SpinLockHolder h(Static::pageheap_lock());
315    span = Static::pageheap()->New(npages);
316    if (span) Static::pageheap()->RegisterSizeClass(span, size_class_);
317  }
318  if (span == NULL) {
319    Log(kLog, __FILE__, __LINE__,
320        "tcmalloc: allocation failed", npages << kPageShift);
321    lock_.Lock();
322    return;
323  }
324  ASSERT(span->length == npages);
325  // Cache sizeclass info eagerly.  Locking is not necessary.
326  // (Instead of being eager, we could just replace any stale info
327  // about this span, but that seems to be no better in practice.)
328  for (int i = 0; i < npages; i++) {
329    Static::pageheap()->CacheSizeClass(span->start + i, size_class_);
330  }
331
332  // Split the block into pieces and add to the free-list
333  // TODO: coloring of objects to avoid cache conflicts?
334  void* list = NULL;
335  char* ptr = reinterpret_cast<char*>(span->start << kPageShift);
336  char* limit = ptr + (npages << kPageShift);
337  const size_t size = Static::sizemap()->ByteSizeForClass(size_class_);
338  int num = 0;
339  while (ptr + size <= limit) {
340    FL_Push(&list, ptr);
341    ptr += size;
342    num++;
343  }
344  ASSERT(ptr <= limit);
345  span->objects = list;
346  span->refcount = 0; // No sub-object in use yet
347
348  // Add span to list of non-empty spans
349  lock_.Lock();
350  tcmalloc::DLL_Prepend(&nonempty_, span);
351  ++num_spans_;
352  counter_ += num;
353}
354
355int CentralFreeList::tc_length() {
356  SpinLockHolder h(&lock_);
357  return used_slots_ * Static::sizemap()->num_objects_to_move(size_class_);
358}
359
360size_t CentralFreeList::OverheadBytes() {
361  SpinLockHolder h(&lock_);
362  if (size_class_ == 0) {  // 0 holds the 0-sized allocations
363    return 0;
364  }
365  const size_t pages_per_span = Static::sizemap()->class_to_pages(size_class_);
366  const size_t object_size = Static::sizemap()->class_to_size(size_class_);
367  ASSERT(object_size > 0);
368  const size_t overhead_per_span = (pages_per_span * kPageSize) % object_size;
369  return num_spans_ * overhead_per_span;
370}
371
372}  // namespace tcmalloc
373