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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 // The eviction policy is a very simple pure LRU, so the elements at the end of | |
6 // the list are evicted until kCleanUpMargin free space is available. There is | |
7 // only one list in use (Rankings::NO_USE), and elements are sent to the front | |
8 // of the list whenever they are accessed. | |
9 | |
10 // The new (in-development) eviction policy adds re-use as a factor to evict | |
11 // an entry. The story so far: | |
12 | |
13 // Entries are linked on separate lists depending on how often they are used. | |
14 // When we see an element for the first time, it goes to the NO_USE list; if | |
15 // the object is reused later on, we move it to the LOW_USE list, until it is | |
16 // used kHighUse times, at which point it is moved to the HIGH_USE list. | |
17 // Whenever an element is evicted, we move it to the DELETED list so that if the | |
18 // element is accessed again, we remember the fact that it was already stored | |
19 // and maybe in the future we don't evict that element. | |
20 | |
21 // When we have to evict an element, first we try to use the last element from | |
22 // the NO_USE list, then we move to the LOW_USE and only then we evict an entry | |
23 // from the HIGH_USE. We attempt to keep entries on the cache for at least | |
24 // kTargetTime hours (with frequently accessed items stored for longer periods), | |
25 // but if we cannot do that, we fall-back to keep each list roughly the same | |
26 // size so that we have a chance to see an element again and move it to another | |
27 // list. | |
28 | |
29 #include "net/disk_cache/blockfile/eviction_v3.h" | |
30 | |
31 #include <stdint.h> | |
32 | |
33 #include <limits> | |
34 | |
35 #include "base/bind.h" | |
36 #include "base/compiler_specific.h" | |
37 #include "base/logging.h" | |
38 #include "base/message_loop/message_loop.h" | |
39 #include "base/strings/string_util.h" | |
40 #include "base/time/time.h" | |
41 #include "net/disk_cache/blockfile/backend_impl_v3.h" | |
42 #include "net/disk_cache/blockfile/entry_impl_v3.h" | |
43 #include "net/disk_cache/blockfile/experiments.h" | |
44 #include "net/disk_cache/blockfile/histogram_macros_v3.h" | |
45 #include "net/disk_cache/blockfile/trace.h" | |
46 | |
47 #define CACHE_UMA_BACKEND_IMPL_OBJ backend_ | |
48 | |
49 using base::Time; | |
50 using base::TimeTicks; | |
51 | |
52 namespace { | |
53 | |
54 const int kCleanUpMargin = 1024 * 1024; | |
55 | |
56 #if defined(V3_NOT_JUST_YET_READY) | |
57 const int kHighUse = 10; // Reuse count to be on the HIGH_USE list. | |
58 const int kTargetTime = 24 * 7; // Time to be evicted (hours since last use). | |
59 const int kMaxDelayedTrims = 60; | |
60 #endif // defined(V3_NOT_JUST_YET_READY). | |
61 | |
62 int LowWaterAdjust(int high_water) { | |
63 if (high_water < kCleanUpMargin) | |
64 return 0; | |
65 | |
66 return high_water - kCleanUpMargin; | |
67 } | |
68 | |
69 #if defined(V3_NOT_JUST_YET_READY) | |
70 bool FallingBehind(int current_size, int max_size) { | |
71 return current_size > max_size - kCleanUpMargin * 20; | |
72 } | |
73 #endif // defined(V3_NOT_JUST_YET_READY). | |
74 | |
75 } // namespace | |
76 | |
77 namespace disk_cache { | |
78 | |
79 // The real initialization happens during Init(), init_ is the only member that | |
80 // has to be initialized here. | |
81 EvictionV3::EvictionV3() | |
82 : backend_(NULL), | |
83 index_(NULL), | |
84 header_(NULL), | |
85 init_(false), | |
86 ptr_factory_(this) { | |
87 } | |
88 | |
89 EvictionV3::~EvictionV3() { | |
90 } | |
91 | |
92 void EvictionV3::Init(BackendImplV3* backend) { | |
93 // We grab a bunch of info from the backend to make the code a little cleaner | |
94 // when we're actually doing work. | |
95 backend_ = backend; | |
96 index_ = &backend_->index_; | |
97 header_ = index_->header(); | |
98 max_size_ = LowWaterAdjust(backend_->max_size_); | |
99 lru_ = backend->lru_eviction_; | |
100 first_trim_ = true; | |
101 trimming_ = false; | |
102 delay_trim_ = false; | |
103 trim_delays_ = 0; | |
104 init_ = true; | |
105 test_mode_ = false; | |
106 } | |
107 | |
108 void EvictionV3::Stop() { | |
109 // It is possible for the backend initialization to fail, in which case this | |
110 // object was never initialized... and there is nothing to do. | |
111 if (!init_) | |
112 return; | |
113 | |
114 // We want to stop further evictions, so let's pretend that we are busy from | |
115 // this point on. | |
116 DCHECK(!trimming_); | |
117 trimming_ = true; | |
118 ptr_factory_.InvalidateWeakPtrs(); | |
119 } | |
120 | |
121 #if defined(V3_NOT_JUST_YET_READY) | |
122 void EvictionV3::TrimCache() { | |
123 if (backend_->disabled_ || trimming_) | |
124 return; | |
125 | |
126 if (!empty && !ShouldTrim()) | |
127 return PostDelayedTrim(); | |
128 | |
129 if (new_eviction_) | |
130 return TrimCacheV2(empty); | |
131 | |
132 Trace("*** Trim Cache ***"); | |
133 trimming_ = true; | |
134 TimeTicks start = TimeTicks::Now(); | |
135 Rankings::ScopedRankingsBlock node(rankings_); | |
136 Rankings::ScopedRankingsBlock next( | |
137 rankings_, rankings_->GetPrev(node.get(), Rankings::NO_USE)); | |
138 int deleted_entries = 0; | |
139 int target_size = empty ? 0 : max_size_; | |
140 while ((header_->num_bytes > target_size || test_mode_) && next.get()) { | |
141 // The iterator could be invalidated within EvictEntry(). | |
142 if (!next->HasData()) | |
143 break; | |
144 node.reset(next.release()); | |
145 next.reset(rankings_->GetPrev(node.get(), Rankings::NO_USE)); | |
146 if (node->Data()->dirty != backend_->GetCurrentEntryId() || empty) { | |
147 // This entry is not being used by anybody. | |
148 // Do NOT use node as an iterator after this point. | |
149 rankings_->TrackRankingsBlock(node.get(), false); | |
150 if (EvictEntry(node.get(), empty, Rankings::NO_USE) && !test_mode_) | |
151 deleted_entries++; | |
152 | |
153 if (!empty && test_mode_) | |
154 break; | |
155 } | |
156 if (!empty && (deleted_entries > 20 || | |
157 (TimeTicks::Now() - start).InMilliseconds() > 20)) { | |
158 base::MessageLoop::current()->PostTask( | |
159 FROM_HERE, | |
160 base::Bind(&EvictionV3::TrimCache, ptr_factory_.GetWeakPtr(), false)); | |
161 break; | |
162 } | |
163 } | |
164 | |
165 if (empty) { | |
166 CACHE_UMA(AGE_MS, "TotalClearTimeV1", 0, start); | |
167 } else { | |
168 CACHE_UMA(AGE_MS, "TotalTrimTimeV1", 0, start); | |
169 } | |
170 CACHE_UMA(COUNTS, "TrimItemsV1", 0, deleted_entries); | |
171 | |
172 trimming_ = false; | |
173 Trace("*** Trim Cache end ***"); | |
174 return; | |
175 } | |
176 | |
177 void EvictionV3::OnOpenEntry(EntryImplV3* entry) { | |
178 EntryStore* info = entry->entry()->Data(); | |
179 DCHECK_EQ(ENTRY_NORMAL, info->state); | |
180 | |
181 if (info->reuse_count < std::numeric_limits<int32_t>::max()) { | |
182 info->reuse_count++; | |
183 entry->entry()->set_modified(); | |
184 | |
185 // We may need to move this to a new list. | |
186 if (1 == info->reuse_count) { | |
187 rankings_->Remove(entry->rankings(), Rankings::NO_USE, true); | |
188 rankings_->Insert(entry->rankings(), false, Rankings::LOW_USE); | |
189 entry->entry()->Store(); | |
190 } else if (kHighUse == info->reuse_count) { | |
191 rankings_->Remove(entry->rankings(), Rankings::LOW_USE, true); | |
192 rankings_->Insert(entry->rankings(), false, Rankings::HIGH_USE); | |
193 entry->entry()->Store(); | |
194 } | |
195 } | |
196 } | |
197 | |
198 void EvictionV3::OnCreateEntry(EntryImplV3* entry) { | |
199 EntryStore* info = entry->entry()->Data(); | |
200 switch (info->state) { | |
201 case ENTRY_NORMAL: { | |
202 DCHECK(!info->reuse_count); | |
203 DCHECK(!info->refetch_count); | |
204 break; | |
205 }; | |
206 case ENTRY_EVICTED: { | |
207 if (info->refetch_count < std::numeric_limits<int32_t>::max()) | |
208 info->refetch_count++; | |
209 | |
210 if (info->refetch_count > kHighUse && info->reuse_count < kHighUse) { | |
211 info->reuse_count = kHighUse; | |
212 } else { | |
213 info->reuse_count++; | |
214 } | |
215 info->state = ENTRY_NORMAL; | |
216 entry->entry()->Store(); | |
217 rankings_->Remove(entry->rankings(), Rankings::DELETED, true); | |
218 break; | |
219 }; | |
220 default: | |
221 NOTREACHED(); | |
222 } | |
223 | |
224 rankings_->Insert(entry->rankings(), true, GetListForEntryV2(entry)); | |
225 } | |
226 | |
227 void EvictionV3::SetTestMode() { | |
228 test_mode_ = true; | |
229 } | |
230 | |
231 void EvictionV3::TrimDeletedList(bool empty) { | |
232 DCHECK(test_mode_ && new_eviction_); | |
233 TrimDeleted(empty); | |
234 } | |
235 | |
236 // ----------------------------------------------------------------------- | |
237 | |
238 void EvictionV3::PostDelayedTrim() { | |
239 // Prevent posting multiple tasks. | |
240 if (delay_trim_) | |
241 return; | |
242 delay_trim_ = true; | |
243 trim_delays_++; | |
244 base::MessageLoop::current()->PostDelayedTask( | |
245 FROM_HERE, | |
246 base::Bind(&EvictionV3::DelayedTrim, ptr_factory_.GetWeakPtr()), | |
247 base::TimeDelta::FromMilliseconds(1000)); | |
248 } | |
249 | |
250 void EvictionV3::DelayedTrim() { | |
251 delay_trim_ = false; | |
252 if (trim_delays_ < kMaxDelayedTrims && backend_->IsLoaded()) | |
253 return PostDelayedTrim(); | |
254 | |
255 TrimCache(false); | |
256 } | |
257 | |
258 bool EvictionV3::ShouldTrim() { | |
259 if (!FallingBehind(header_->num_bytes, max_size_) && | |
260 trim_delays_ < kMaxDelayedTrims && backend_->IsLoaded()) { | |
261 return false; | |
262 } | |
263 | |
264 UMA_HISTOGRAM_COUNTS("DiskCache.TrimDelays", trim_delays_); | |
265 trim_delays_ = 0; | |
266 return true; | |
267 } | |
268 | |
269 bool EvictionV3::ShouldTrimDeleted() { | |
270 int index_load = header_->num_entries * 100 / index_size_; | |
271 | |
272 // If the index is not loaded, the deleted list will tend to double the size | |
273 // of the other lists 3 lists (40% of the total). Otherwise, all lists will be | |
274 // about the same size. | |
275 int max_length = (index_load < 25) ? header_->num_entries * 2 / 5 : | |
276 header_->num_entries / 4; | |
277 return (!test_mode_ && header_->lru.sizes[Rankings::DELETED] > max_length); | |
278 } | |
279 | |
280 bool Eviction::EvictEntry(CacheRankingsBlock* node, bool empty, | |
281 Rankings::List list) { | |
282 EntryImplV3* entry = backend_->GetEnumeratedEntry(node, list); | |
283 if (!entry) { | |
284 Trace("NewEntry failed on Trim 0x%x", node->address().value()); | |
285 return false; | |
286 } | |
287 | |
288 ReportTrimTimes(entry); | |
289 if (empty || !new_eviction_) { | |
290 entry->DoomImpl(); | |
291 } else { | |
292 entry->DeleteEntryData(false); | |
293 EntryStore* info = entry->entry()->Data(); | |
294 DCHECK_EQ(ENTRY_NORMAL, info->state); | |
295 | |
296 rankings_->Remove(entry->rankings(), GetListForEntryV2(entry), true); | |
297 info->state = ENTRY_EVICTED; | |
298 entry->entry()->Store(); | |
299 rankings_->Insert(entry->rankings(), true, Rankings::DELETED); | |
300 } | |
301 if (!empty) | |
302 backend_->OnEvent(Stats::TRIM_ENTRY); | |
303 | |
304 entry->Release(); | |
305 | |
306 return true; | |
307 } | |
308 | |
309 void EvictionV3::TrimCacheV2(bool empty) { | |
310 Trace("*** Trim Cache ***"); | |
311 trimming_ = true; | |
312 TimeTicks start = TimeTicks::Now(); | |
313 | |
314 const int kListsToSearch = 3; | |
315 Rankings::ScopedRankingsBlock next[kListsToSearch]; | |
316 int list = Rankings::LAST_ELEMENT; | |
317 | |
318 // Get a node from each list. | |
319 for (int i = 0; i < kListsToSearch; i++) { | |
320 bool done = false; | |
321 next[i].set_rankings(rankings_); | |
322 if (done) | |
323 continue; | |
324 next[i].reset(rankings_->GetPrev(NULL, static_cast<Rankings::List>(i))); | |
325 if (!empty && NodeIsOldEnough(next[i].get(), i)) { | |
326 list = static_cast<Rankings::List>(i); | |
327 done = true; | |
328 } | |
329 } | |
330 | |
331 // If we are not meeting the time targets lets move on to list length. | |
332 if (!empty && Rankings::LAST_ELEMENT == list) | |
333 list = SelectListByLength(next); | |
334 | |
335 if (empty) | |
336 list = 0; | |
337 | |
338 Rankings::ScopedRankingsBlock node(rankings_); | |
339 int deleted_entries = 0; | |
340 int target_size = empty ? 0 : max_size_; | |
341 | |
342 for (; list < kListsToSearch; list++) { | |
343 while ((header_->num_bytes > target_size || test_mode_) && | |
344 next[list].get()) { | |
345 // The iterator could be invalidated within EvictEntry(). | |
346 if (!next[list]->HasData()) | |
347 break; | |
348 node.reset(next[list].release()); | |
349 next[list].reset(rankings_->GetPrev(node.get(), | |
350 static_cast<Rankings::List>(list))); | |
351 if (node->Data()->dirty != backend_->GetCurrentEntryId() || empty) { | |
352 // This entry is not being used by anybody. | |
353 // Do NOT use node as an iterator after this point. | |
354 rankings_->TrackRankingsBlock(node.get(), false); | |
355 if (EvictEntry(node.get(), empty, static_cast<Rankings::List>(list))) | |
356 deleted_entries++; | |
357 | |
358 if (!empty && test_mode_) | |
359 break; | |
360 } | |
361 if (!empty && (deleted_entries > 20 || | |
362 (TimeTicks::Now() - start).InMilliseconds() > 20)) { | |
363 base::MessageLoop::current()->PostTask( | |
364 FROM_HERE, | |
365 base::Bind(&Eviction::TrimCache, ptr_factory_.GetWeakPtr(), false)); | |
366 break; | |
367 } | |
368 } | |
369 if (!empty) | |
370 list = kListsToSearch; | |
371 } | |
372 | |
373 if (empty) { | |
374 TrimDeleted(true); | |
375 } else if (ShouldTrimDeleted()) { | |
376 base::MessageLoop::current()->PostTask( | |
377 FROM_HERE, | |
378 base::Bind(&EvictionV3::TrimDeleted, ptr_factory_.GetWeakPtr(), empty)); | |
379 } | |
380 | |
381 if (empty) { | |
382 CACHE_UMA(AGE_MS, "TotalClearTimeV2", 0, start); | |
383 } else { | |
384 CACHE_UMA(AGE_MS, "TotalTrimTimeV2", 0, start); | |
385 } | |
386 CACHE_UMA(COUNTS, "TrimItemsV2", 0, deleted_entries); | |
387 | |
388 Trace("*** Trim Cache end ***"); | |
389 trimming_ = false; | |
390 return; | |
391 } | |
392 | |
393 // This is a minimal implementation that just discards the oldest nodes. | |
394 // TODO(rvargas): Do something better here. | |
395 void EvictionV3::TrimDeleted(bool empty) { | |
396 Trace("*** Trim Deleted ***"); | |
397 if (backend_->disabled_) | |
398 return; | |
399 | |
400 TimeTicks start = TimeTicks::Now(); | |
401 Rankings::ScopedRankingsBlock node(rankings_); | |
402 Rankings::ScopedRankingsBlock next( | |
403 rankings_, rankings_->GetPrev(node.get(), Rankings::DELETED)); | |
404 int deleted_entries = 0; | |
405 while (next.get() && | |
406 (empty || (deleted_entries < 20 && | |
407 (TimeTicks::Now() - start).InMilliseconds() < 20))) { | |
408 node.reset(next.release()); | |
409 next.reset(rankings_->GetPrev(node.get(), Rankings::DELETED)); | |
410 if (RemoveDeletedNode(node.get())) | |
411 deleted_entries++; | |
412 if (test_mode_) | |
413 break; | |
414 } | |
415 | |
416 if (deleted_entries && !empty && ShouldTrimDeleted()) { | |
417 base::MessageLoop::current()->PostTask( | |
418 FROM_HERE, | |
419 base::Bind(&EvictionV3::TrimDeleted, ptr_factory_.GetWeakPtr(), false)); | |
420 } | |
421 | |
422 CACHE_UMA(AGE_MS, "TotalTrimDeletedTime", 0, start); | |
423 CACHE_UMA(COUNTS, "TrimDeletedItems", 0, deleted_entries); | |
424 Trace("*** Trim Deleted end ***"); | |
425 return; | |
426 } | |
427 | |
428 void EvictionV3::ReportTrimTimes(EntryImplV3* entry) { | |
429 if (first_trim_) { | |
430 first_trim_ = false; | |
431 if (backend_->ShouldReportAgain()) { | |
432 CACHE_UMA(AGE, "TrimAge", 0, entry->GetLastUsed()); | |
433 ReportListStats(); | |
434 } | |
435 | |
436 if (header_->lru.filled) | |
437 return; | |
438 | |
439 header_->lru.filled = 1; | |
440 | |
441 if (header_->create_time) { | |
442 // This is the first entry that we have to evict, generate some noise. | |
443 backend_->FirstEviction(); | |
444 } else { | |
445 // This is an old file, but we may want more reports from this user so | |
446 // lets save some create_time. | |
447 Time::Exploded old = {0}; | |
448 old.year = 2009; | |
449 old.month = 3; | |
450 old.day_of_month = 1; | |
451 header_->create_time = Time::FromLocalExploded(old).ToInternalValue(); | |
452 } | |
453 } | |
454 } | |
455 | |
456 bool EvictionV3::NodeIsOldEnough(CacheRankingsBlock* node, int list) { | |
457 if (!node) | |
458 return false; | |
459 | |
460 // If possible, we want to keep entries on each list at least kTargetTime | |
461 // hours. Each successive list on the enumeration has 2x the target time of | |
462 // the previous list. | |
463 Time used = Time::FromInternalValue(node->Data()->last_used); | |
464 int multiplier = 1 << list; | |
465 return (Time::Now() - used).InHours() > kTargetTime * multiplier; | |
466 } | |
467 | |
468 int EvictionV3::SelectListByLength(Rankings::ScopedRankingsBlock* next) { | |
469 int data_entries = header_->num_entries - | |
470 header_->lru.sizes[Rankings::DELETED]; | |
471 // Start by having each list to be roughly the same size. | |
472 if (header_->lru.sizes[0] > data_entries / 3) | |
473 return 0; | |
474 | |
475 int list = (header_->lru.sizes[1] > data_entries / 3) ? 1 : 2; | |
476 | |
477 // Make sure that frequently used items are kept for a minimum time; we know | |
478 // that this entry is not older than its current target, but it must be at | |
479 // least older than the target for list 0 (kTargetTime), as long as we don't | |
480 // exhaust list 0. | |
481 if (!NodeIsOldEnough(next[list].get(), 0) && | |
482 header_->lru.sizes[0] > data_entries / 10) | |
483 list = 0; | |
484 | |
485 return list; | |
486 } | |
487 | |
488 void EvictionV3::ReportListStats() { | |
489 if (!new_eviction_) | |
490 return; | |
491 | |
492 Rankings::ScopedRankingsBlock last1(rankings_, | |
493 rankings_->GetPrev(NULL, Rankings::NO_USE)); | |
494 Rankings::ScopedRankingsBlock last2(rankings_, | |
495 rankings_->GetPrev(NULL, Rankings::LOW_USE)); | |
496 Rankings::ScopedRankingsBlock last3(rankings_, | |
497 rankings_->GetPrev(NULL, Rankings::HIGH_USE)); | |
498 Rankings::ScopedRankingsBlock last4(rankings_, | |
499 rankings_->GetPrev(NULL, Rankings::DELETED)); | |
500 | |
501 if (last1.get()) | |
502 CACHE_UMA(AGE, "NoUseAge", 0, | |
503 Time::FromInternalValue(last1.get()->Data()->last_used)); | |
504 if (last2.get()) | |
505 CACHE_UMA(AGE, "LowUseAge", 0, | |
506 Time::FromInternalValue(last2.get()->Data()->last_used)); | |
507 if (last3.get()) | |
508 CACHE_UMA(AGE, "HighUseAge", 0, | |
509 Time::FromInternalValue(last3.get()->Data()->last_used)); | |
510 if (last4.get()) | |
511 CACHE_UMA(AGE, "DeletedAge", 0, | |
512 Time::FromInternalValue(last4.get()->Data()->last_used)); | |
513 } | |
514 #endif // defined(V3_NOT_JUST_YET_READY). | |
515 | |
516 } // namespace disk_cache | |
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