net/disk_cache/v3/eviction_v3.cc

   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/eviction.h"
  30
  31 #include "base/bind.h"
  32 #include "base/compiler_specific.h"
  33 #include "base/logging.h"
  34 #include "base/message_loop/message_loop.h"
  35 #include "base/strings/string_util.h"
  36 #include "base/time/time.h"
  37 #include "net/disk_cache/backend_impl.h"
  38 #include "net/disk_cache/entry_impl.h"
  39 #include "net/disk_cache/experiments.h"
  40 #include "net/disk_cache/histogram_macros.h"
  41 #include "net/disk_cache/trace.h"
  42
  43 using base::Time;
  44 using base::TimeTicks;
  45
  46 namespace {
  47
  48 const int kCleanUpMargin = 1024 * 1024;
  49 const int kHighUse = 10;  // Reuse count to be on the HIGH_USE list.
  50 const int kTargetTime = 24 * 7;  // Time to be evicted (hours since last use).
  51 const int kMaxDelayedTrims = 60;
  52
  53 int LowWaterAdjust(int high_water) {
  54   if (high_water < kCleanUpMargin)
  55     return 0;
  56
  57   return high_water - kCleanUpMargin;
  58 }
  59
  60 bool FallingBehind(int current_size, int max_size) {
  61   return current_size > max_size - kCleanUpMargin * 20;
  62 }
  63
  64 }  // namespace
  65
  66 namespace disk_cache {
  67
  68 // The real initialization happens during Init(), init_ is the only member that
  69 // has to be initialized here.
  70 Eviction::Eviction()
  71     : backend_(NULL),
  72       init_(false),
  73       ptr_factory_(this) {
  74 }
  75
  76 Eviction::~Eviction() {
  77 }
  78
  79 void Eviction::Init(BackendImpl* backend) {
  80   // We grab a bunch of info from the backend to make the code a little cleaner
  81   // when we're actually doing work.
  82   backend_ = backend;
  83   rankings_ = &backend->rankings_;
  84   header_ = &backend_->data_->header;
  85   max_size_ = LowWaterAdjust(backend_->max_size_);
  86   index_size_ = backend->mask_ + 1;
  87   new_eviction_ = backend->new_eviction_;
  88   first_trim_ = true;
  89   trimming_ = false;
  90   delay_trim_ = false;
  91   trim_delays_ = 0;
  92   init_ = true;
  93   test_mode_ = false;
  94 }
  95
  96 void Eviction::Stop() {
  97   // It is possible for the backend initialization to fail, in which case this
  98   // object was never initialized... and there is nothing to do.
  99   if (!init_)
 100     return;
 101
 102   // We want to stop further evictions, so let's pretend that we are busy from
 103   // this point on.
 104   DCHECK(!trimming_);
 105   trimming_ = true;
 106   ptr_factory_.InvalidateWeakPtrs();
 107 }
 108
 109 void Eviction::TrimCache(bool empty) {
 110   if (backend_->disabled_ || trimming_)
 111     return;
 112
 113   if (!empty && !ShouldTrim())
 114     return PostDelayedTrim();
 115
 116   if (new_eviction_)
 117     return TrimCacheV2(empty);
 118
 119   Trace("*** Trim Cache ***");
 120   trimming_ = true;
 121   TimeTicks start = TimeTicks::Now();
 122   Rankings::ScopedRankingsBlock node(rankings_);
 123   Rankings::ScopedRankingsBlock next(
 124       rankings_, rankings_->GetPrev(node.get(), Rankings::NO_USE));
 125   int deleted_entries = 0;
 126   int target_size = empty ? 0 : max_size_;
 127   while ((header_->num_bytes > target_size || test_mode_) && next.get()) {
 128     // The iterator could be invalidated within EvictEntry().
 129     if (!next->HasData())
 130       break;
 131     node.reset(next.release());
 132     next.reset(rankings_->GetPrev(node.get(), Rankings::NO_USE));
 133     if (node->Data()->dirty != backend_->GetCurrentEntryId() || empty) {
 134       // This entry is not being used by anybody.
 135       // Do NOT use node as an iterator after this point.
 136       rankings_->TrackRankingsBlock(node.get(), false);
 137       if (EvictEntry(node.get(), empty, Rankings::NO_USE) && !test_mode_)
 138         deleted_entries++;
 139
 140       if (!empty && test_mode_)
 141         break;
 142     }
 143     if (!empty && (deleted_entries > 20 ||
 144                    (TimeTicks::Now() - start).InMilliseconds() > 20)) {
 145       base::MessageLoop::current()->PostTask(
 146           FROM_HERE,
 147           base::Bind(&Eviction::TrimCache, ptr_factory_.GetWeakPtr(), false));
 148       break;
 149     }
 150   }
 151
 152   if (empty) {
 153     CACHE_UMA(AGE_MS, "TotalClearTimeV1", 0, start);
 154   } else {
 155     CACHE_UMA(AGE_MS, "TotalTrimTimeV1", 0, start);
 156   }
 157   CACHE_UMA(COUNTS, "TrimItemsV1", 0, deleted_entries);
 158
 159   trimming_ = false;
 160   Trace("*** Trim Cache end ***");
 161   return;
 162 }
 163
 164 void Eviction::OnOpenEntryV2(EntryImpl* entry) {
 165   EntryStore* info = entry->entry()->Data();
 166   DCHECK_EQ(ENTRY_NORMAL, info->state);
 167
 168   if (info->reuse_count < kint32max) {
 169     info->reuse_count++;
 170     entry->entry()->set_modified();
 171
 172     // We may need to move this to a new list.
 173     if (1 == info->reuse_count) {
 174       rankings_->Remove(entry->rankings(), Rankings::NO_USE, true);
 175       rankings_->Insert(entry->rankings(), false, Rankings::LOW_USE);
 176       entry->entry()->Store();
 177     } else if (kHighUse == info->reuse_count) {
 178       rankings_->Remove(entry->rankings(), Rankings::LOW_USE, true);
 179       rankings_->Insert(entry->rankings(), false, Rankings::HIGH_USE);
 180       entry->entry()->Store();
 181     }
 182   }
 183 }
 184
 185 void Eviction::OnCreateEntryV2(EntryImpl* entry) {
 186   EntryStore* info = entry->entry()->Data();
 187   switch (info->state) {
 188     case ENTRY_NORMAL: {
 189       DCHECK(!info->reuse_count);
 190       DCHECK(!info->refetch_count);
 191       break;
 192     };
 193     case ENTRY_EVICTED: {
 194       if (info->refetch_count < kint32max)
 195         info->refetch_count++;
 196
 197       if (info->refetch_count > kHighUse && info->reuse_count < kHighUse) {
 198         info->reuse_count = kHighUse;
 199       } else {
 200         info->reuse_count++;
 201       }
 202       info->state = ENTRY_NORMAL;
 203       entry->entry()->Store();
 204       rankings_->Remove(entry->rankings(), Rankings::DELETED, true);
 205       break;
 206     };
 207     default:
 208       NOTREACHED();
 209   }
 210
 211   rankings_->Insert(entry->rankings(), true, GetListForEntryV2(entry));
 212 }
 213
 214 void Eviction::SetTestMode() {
 215   test_mode_ = true;
 216 }
 217
 218 void Eviction::TrimDeletedList(bool empty) {
 219   DCHECK(test_mode_ && new_eviction_);
 220   TrimDeleted(empty);
 221 }
 222
 223 // -----------------------------------------------------------------------
 224
 225 void Eviction::PostDelayedTrim() {
 226   // Prevent posting multiple tasks.
 227   if (delay_trim_)
 228     return;
 229   delay_trim_ = true;
 230   trim_delays_++;
 231   base::MessageLoop::current()->PostDelayedTask(
 232       FROM_HERE,
 233       base::Bind(&Eviction::DelayedTrim, ptr_factory_.GetWeakPtr()),
 234       base::TimeDelta::FromMilliseconds(1000));
 235 }
 236
 237 void Eviction::DelayedTrim() {
 238   delay_trim_ = false;
 239   if (trim_delays_ < kMaxDelayedTrims && backend_->IsLoaded())
 240     return PostDelayedTrim();
 241
 242   TrimCache(false);
 243 }
 244
 245 bool Eviction::ShouldTrim() {
 246   if (!FallingBehind(header_->num_bytes, max_size_) &&
 247       trim_delays_ < kMaxDelayedTrims && backend_->IsLoaded()) {
 248     return false;
 249   }
 250
 251   UMA_HISTOGRAM_COUNTS("DiskCache.TrimDelays", trim_delays_);
 252   trim_delays_ = 0;
 253   return true;
 254 }
 255
 256 bool Eviction::ShouldTrimDeleted() {
 257   int index_load = header_->num_entries * 100 / index_size_;
 258
 259   // If the index is not loaded, the deleted list will tend to double the size
 260   // of the other lists 3 lists (40% of the total). Otherwise, all lists will be
 261   // about the same size.
 262   int max_length = (index_load < 25) ? header_->num_entries * 2 / 5 :
 263                                        header_->num_entries / 4;
 264   return (!test_mode_ && header_->lru.sizes[Rankings::DELETED] > max_length);
 265 }
 266
 267 bool Eviction::EvictEntry(CacheRankingsBlock* node, bool empty,
 268                           Rankings::List list) {
 269   EntryImpl* entry = backend_->GetEnumeratedEntry(node, list);
 270   if (!entry) {
 271     Trace("NewEntry failed on Trim 0x%x", node->address().value());
 272     return false;
 273   }
 274
 275   ReportTrimTimes(entry);
 276   if (empty || !new_eviction_) {
 277     entry->DoomImpl();
 278   } else {
 279     entry->DeleteEntryData(false);
 280     EntryStore* info = entry->entry()->Data();
 281     DCHECK_EQ(ENTRY_NORMAL, info->state);
 282
 283     rankings_->Remove(entry->rankings(), GetListForEntryV2(entry), true);
 284     info->state = ENTRY_EVICTED;
 285     entry->entry()->Store();
 286     rankings_->Insert(entry->rankings(), true, Rankings::DELETED);
 287   }
 288   if (!empty)
 289     backend_->OnEvent(Stats::TRIM_ENTRY);
 290
 291   entry->Release();
 292
 293   return true;
 294 }
 295
 296 void Eviction::TrimCacheV2(bool empty) {
 297   Trace("*** Trim Cache ***");
 298   trimming_ = true;
 299   TimeTicks start = TimeTicks::Now();
 300
 301   const int kListsToSearch = 3;
 302   Rankings::ScopedRankingsBlock next[kListsToSearch];
 303   int list = Rankings::LAST_ELEMENT;
 304
 305   // Get a node from each list.
 306   for (int i = 0; i < kListsToSearch; i++) {
 307     bool done = false;
 308     next[i].set_rankings(rankings_);
 309     if (done)
 310       continue;
 311     next[i].reset(rankings_->GetPrev(NULL, static_cast<Rankings::List>(i)));
 312     if (!empty && NodeIsOldEnough(next[i].get(), i)) {
 313       list = static_cast<Rankings::List>(i);
 314       done = true;
 315     }
 316   }
 317
 318   // If we are not meeting the time targets lets move on to list length.
 319   if (!empty && Rankings::LAST_ELEMENT == list)
 320     list = SelectListByLength(next);
 321
 322   if (empty)
 323     list = 0;
 324
 325   Rankings::ScopedRankingsBlock node(rankings_);
 326   int deleted_entries = 0;
 327   int target_size = empty ? 0 : max_size_;
 328
 329   for (; list < kListsToSearch; list++) {
 330     while ((header_->num_bytes > target_size || test_mode_) &&
 331            next[list].get()) {
 332       // The iterator could be invalidated within EvictEntry().
 333       if (!next[list]->HasData())
 334         break;
 335       node.reset(next[list].release());
 336       next[list].reset(rankings_->GetPrev(node.get(),
 337                                           static_cast<Rankings::List>(list)));
 338       if (node->Data()->dirty != backend_->GetCurrentEntryId() || empty) {
 339         // This entry is not being used by anybody.
 340         // Do NOT use node as an iterator after this point.
 341         rankings_->TrackRankingsBlock(node.get(), false);
 342         if (EvictEntry(node.get(), empty, static_cast<Rankings::List>(list)))
 343           deleted_entries++;
 344
 345         if (!empty && test_mode_)
 346           break;
 347       }
 348       if (!empty && (deleted_entries > 20 ||
 349                      (TimeTicks::Now() - start).InMilliseconds() > 20)) {
 350         base::MessageLoop::current()->PostTask(
 351             FROM_HERE,
 352             base::Bind(&Eviction::TrimCache, ptr_factory_.GetWeakPtr(), false));
 353         break;
 354       }
 355     }
 356     if (!empty)
 357       list = kListsToSearch;
 358   }
 359
 360   if (empty) {
 361     TrimDeleted(true);
 362   } else if (ShouldTrimDeleted()) {
 363     base::MessageLoop::current()->PostTask(
 364         FROM_HERE,
 365         base::Bind(&Eviction::TrimDeleted, ptr_factory_.GetWeakPtr(), empty));
 366   }
 367
 368   if (empty) {
 369     CACHE_UMA(AGE_MS, "TotalClearTimeV2", 0, start);
 370   } else {
 371     CACHE_UMA(AGE_MS, "TotalTrimTimeV2", 0, start);
 372   }
 373   CACHE_UMA(COUNTS, "TrimItemsV2", 0, deleted_entries);
 374
 375   Trace("*** Trim Cache end ***");
 376   trimming_ = false;
 377   return;
 378 }
 379
 380 // This is a minimal implementation that just discards the oldest nodes.
 381 // TODO(rvargas): Do something better here.
 382 void Eviction::TrimDeleted(bool empty) {
 383   Trace("*** Trim Deleted ***");
 384   if (backend_->disabled_)
 385     return;
 386
 387   TimeTicks start = TimeTicks::Now();
 388   Rankings::ScopedRankingsBlock node(rankings_);
 389   Rankings::ScopedRankingsBlock next(
 390     rankings_, rankings_->GetPrev(node.get(), Rankings::DELETED));
 391   int deleted_entries = 0;
 392   while (next.get() &&
 393          (empty || (deleted_entries < 20 &&
 394                     (TimeTicks::Now() - start).InMilliseconds() < 20))) {
 395     node.reset(next.release());
 396     next.reset(rankings_->GetPrev(node.get(), Rankings::DELETED));
 397     if (RemoveDeletedNode(node.get()))
 398       deleted_entries++;
 399     if (test_mode_)
 400       break;
 401   }
 402
 403   if (deleted_entries && !empty && ShouldTrimDeleted()) {
 404     base::MessageLoop::current()->PostTask(
 405         FROM_HERE,
 406         base::Bind(&Eviction::TrimDeleted, ptr_factory_.GetWeakPtr(), false));
 407   }
 408
 409   CACHE_UMA(AGE_MS, "TotalTrimDeletedTime", 0, start);
 410   CACHE_UMA(COUNTS, "TrimDeletedItems", 0, deleted_entries);
 411   Trace("*** Trim Deleted end ***");
 412   return;
 413 }
 414
 415 void Eviction::ReportTrimTimes(EntryImpl* entry) {
 416   if (first_trim_) {
 417     first_trim_ = false;
 418     if (backend_->ShouldReportAgain()) {
 419       CACHE_UMA(AGE, "TrimAge", 0, entry->GetLastUsed());
 420       ReportListStats();
 421     }
 422
 423     if (header_->lru.filled)
 424       return;
 425
 426     header_->lru.filled = 1;
 427
 428     if (header_->create_time) {
 429       // This is the first entry that we have to evict, generate some noise.
 430       backend_->FirstEviction();
 431     } else {
 432       // This is an old file, but we may want more reports from this user so
 433       // lets save some create_time.
 434       Time::Exploded old = {0};
 435       old.year = 2009;
 436       old.month = 3;
 437       old.day_of_month = 1;
 438       header_->create_time = Time::FromLocalExploded(old).ToInternalValue();
 439     }
 440   }
 441 }
 442
 443 bool Eviction::NodeIsOldEnough(CacheRankingsBlock* node, int list) {
 444   if (!node)
 445     return false;
 446
 447   // If possible, we want to keep entries on each list at least kTargetTime
 448   // hours. Each successive list on the enumeration has 2x the target time of
 449   // the previous list.
 450   Time used = Time::FromInternalValue(node->Data()->last_used);
 451   int multiplier = 1 << list;
 452   return (Time::Now() - used).InHours() > kTargetTime * multiplier;
 453 }
 454
 455 int Eviction::SelectListByLength(Rankings::ScopedRankingsBlock* next) {
 456   int data_entries = header_->num_entries -
 457                      header_->lru.sizes[Rankings::DELETED];
 458   // Start by having each list to be roughly the same size.
 459   if (header_->lru.sizes[0] > data_entries / 3)
 460     return 0;
 461
 462   int list = (header_->lru.sizes[1] > data_entries / 3) ? 1 : 2;
 463
 464   // Make sure that frequently used items are kept for a minimum time; we know
 465   // that this entry is not older than its current target, but it must be at
 466   // least older than the target for list 0 (kTargetTime), as long as we don't
 467   // exhaust list 0.
 468   if (!NodeIsOldEnough(next[list].get(), 0) &&
 469       header_->lru.sizes[0] > data_entries / 10)
 470     list = 0;
 471
 472   return list;
 473 }
 474
 475 void Eviction::ReportListStats() {
 476   if (!new_eviction_)
 477     return;
 478
 479   Rankings::ScopedRankingsBlock last1(rankings_,
 480       rankings_->GetPrev(NULL, Rankings::NO_USE));
 481   Rankings::ScopedRankingsBlock last2(rankings_,
 482       rankings_->GetPrev(NULL, Rankings::LOW_USE));
 483   Rankings::ScopedRankingsBlock last3(rankings_,
 484       rankings_->GetPrev(NULL, Rankings::HIGH_USE));
 485   Rankings::ScopedRankingsBlock last4(rankings_,
 486       rankings_->GetPrev(NULL, Rankings::DELETED));
 487
 488   if (last1.get())
 489     CACHE_UMA(AGE, "NoUseAge", 0,
 490               Time::FromInternalValue(last1.get()->Data()->last_used));
 491   if (last2.get())
 492     CACHE_UMA(AGE, "LowUseAge", 0,
 493               Time::FromInternalValue(last2.get()->Data()->last_used));
 494   if (last3.get())
 495     CACHE_UMA(AGE, "HighUseAge", 0,
 496               Time::FromInternalValue(last3.get()->Data()->last_used));
 497   if (last4.get())
 498     CACHE_UMA(AGE, "DeletedAge", 0,
 499               Time::FromInternalValue(last4.get()->Data()->last_used));
 500 }
 501
 502 }  // namespace disk_cache