blob: fd24d025afccd2407c1e4b29586c8700637d1824 [file] [log] [blame]
// Copyright (c) 2011 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.
// The eviction policy is a very simple pure LRU, so the elements at the end of
// the list are evicted until kCleanUpMargin free space is available. There is
// only one list in use (Rankings::NO_USE), and elements are sent to the front
// of the list whenever they are accessed.
// The new (in-development) eviction policy adds re-use as a factor to evict
// an entry. The story so far:
// Entries are linked on separate lists depending on how often they are used.
// When we see an element for the first time, it goes to the NO_USE list; if
// the object is reused later on, we move it to the LOW_USE list, until it is
// used kHighUse times, at which point it is moved to the HIGH_USE list.
// Whenever an element is evicted, we move it to the DELETED list so that if the
// element is accessed again, we remember the fact that it was already stored
// and maybe in the future we don't evict that element.
// When we have to evict an element, first we try to use the last element from
// the NO_USE list, then we move to the LOW_USE and only then we evict an entry
// from the HIGH_USE. We attempt to keep entries on the cache for at least
// kTargetTime hours (with frequently accessed items stored for longer periods),
// but if we cannot do that, we fall-back to keep each list roughly the same
// size so that we have a chance to see an element again and move it to another
// list.
#include "net/disk_cache/eviction.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/message_loop.h"
#include "base/string_util.h"
#include "base/time.h"
#include "net/disk_cache/backend_impl.h"
#include "net/disk_cache/entry_impl.h"
#include "net/disk_cache/experiments.h"
#include "net/disk_cache/histogram_macros.h"
#include "net/disk_cache/trace.h"
using base::Time;
using base::TimeTicks;
namespace {
const int kCleanUpMargin = 1024 * 1024;
const int kHighUse = 10; // Reuse count to be on the HIGH_USE list.
const int kTargetTime = 24 * 7; // Time to be evicted (hours since last use).
const int kMaxDelayedTrims = 60;
int LowWaterAdjust(int high_water) {
if (high_water < kCleanUpMargin)
return 0;
return high_water - kCleanUpMargin;
}
} // namespace
namespace disk_cache {
Eviction::Eviction()
: backend_(NULL),
init_(false),
ALLOW_THIS_IN_INITIALIZER_LIST(factory_(this)) {
}
Eviction::~Eviction() {
}
void Eviction::Init(BackendImpl* backend) {
// We grab a bunch of info from the backend to make the code a little cleaner
// when we're actually doing work.
backend_ = backend;
rankings_ = &backend->rankings_;
header_ = &backend_->data_->header;
max_size_ = LowWaterAdjust(backend_->max_size_);
new_eviction_ = backend->new_eviction_;
first_trim_ = true;
trimming_ = false;
delay_trim_ = false;
trim_delays_ = 0;
init_ = true;
test_mode_ = false;
in_experiment_ = (header_->experiment == EXPERIMENT_DELETED_LIST_IN);
}
void Eviction::Stop() {
// It is possible for the backend initialization to fail, in which case this
// object was never initialized... and there is nothing to do.
if (!init_)
return;
// We want to stop further evictions, so let's pretend that we are busy from
// this point on.
DCHECK(!trimming_);
trimming_ = true;
factory_.RevokeAll();
}
void Eviction::TrimCache(bool empty) {
if (backend_->disabled_ || trimming_)
return;
if (!empty && !ShouldTrim())
return PostDelayedTrim();
if (new_eviction_)
return TrimCacheV2(empty);
Trace("*** Trim Cache ***");
trimming_ = true;
TimeTicks start = TimeTicks::Now();
Rankings::ScopedRankingsBlock node(rankings_);
Rankings::ScopedRankingsBlock next(rankings_,
rankings_->GetPrev(node.get(), Rankings::NO_USE));
int target_size = empty ? 0 : max_size_;
while ((header_->num_bytes > target_size && next.get()) || test_mode_) {
// The iterator could be invalidated within EvictEntry().
if (!next->HasData())
break;
node.reset(next.release());
next.reset(rankings_->GetPrev(node.get(), Rankings::NO_USE));
if (node->Data()->dirty != backend_->GetCurrentEntryId() || empty) {
// This entry is not being used by anybody.
// Do NOT use node as an iterator after this point.
rankings_->TrackRankingsBlock(node.get(), false);
if (!EvictEntry(node.get(), empty) && !test_mode_)
continue;
if (!empty) {
backend_->OnEvent(Stats::TRIM_ENTRY);
if (test_mode_)
break;
if ((TimeTicks::Now() - start).InMilliseconds() > 20) {
MessageLoop::current()->PostTask(FROM_HERE,
factory_.NewRunnableMethod(&Eviction::TrimCache, false));
break;
}
}
}
}
if (empty) {
CACHE_UMA(AGE_MS, "TotalClearTimeV1", 0, start);
} else {
CACHE_UMA(AGE_MS, "TotalTrimTimeV1", backend_->GetSizeGroup(), start);
}
trimming_ = false;
Trace("*** Trim Cache end ***");
return;
}
void Eviction::UpdateRank(EntryImpl* entry, bool modified) {
if (new_eviction_)
return UpdateRankV2(entry, modified);
rankings_->UpdateRank(entry->rankings(), modified, GetListForEntry(entry));
}
void Eviction::OnOpenEntry(EntryImpl* entry) {
if (new_eviction_)
return OnOpenEntryV2(entry);
}
void Eviction::OnCreateEntry(EntryImpl* entry) {
if (new_eviction_)
return OnCreateEntryV2(entry);
rankings_->Insert(entry->rankings(), true, GetListForEntry(entry));
}
void Eviction::OnDoomEntry(EntryImpl* entry) {
if (new_eviction_)
return OnDoomEntryV2(entry);
rankings_->Remove(entry->rankings(), GetListForEntry(entry));
}
void Eviction::OnDestroyEntry(EntryImpl* entry) {
if (new_eviction_)
return OnDestroyEntryV2(entry);
}
void Eviction::SetTestMode() {
test_mode_ = true;
}
void Eviction::TrimDeletedList(bool empty) {
DCHECK(test_mode_ && new_eviction_);
TrimDeleted(empty);
}
void Eviction::PostDelayedTrim() {
// Prevent posting multiple tasks.
if (delay_trim_)
return;
delay_trim_ = true;
trim_delays_++;
MessageLoop::current()->PostDelayedTask(FROM_HERE,
factory_.NewRunnableMethod(&Eviction::DelayedTrim), 1000);
}
void Eviction::DelayedTrim() {
delay_trim_ = false;
if (trim_delays_ < kMaxDelayedTrims && backend_->IsLoaded())
return PostDelayedTrim();
TrimCache(false);
}
bool Eviction::ShouldTrim() {
if (trim_delays_ < kMaxDelayedTrims && backend_->IsLoaded())
return false;
UMA_HISTOGRAM_COUNTS("DiskCache.TrimDelays", trim_delays_);
trim_delays_ = 0;
return true;
}
void Eviction::ReportTrimTimes(EntryImpl* entry) {
if (first_trim_) {
first_trim_ = false;
if (backend_->ShouldReportAgain()) {
CACHE_UMA(AGE, "TrimAge", 0, entry->GetLastUsed());
ReportListStats();
}
if (header_->lru.filled)
return;
header_->lru.filled = 1;
if (header_->create_time) {
// This is the first entry that we have to evict, generate some noise.
backend_->FirstEviction();
in_experiment_ = (header_->experiment == EXPERIMENT_DELETED_LIST_IN);
} else {
// This is an old file, but we may want more reports from this user so
// lets save some create_time.
Time::Exploded old = {0};
old.year = 2009;
old.month = 3;
old.day_of_month = 1;
header_->create_time = Time::FromLocalExploded(old).ToInternalValue();
}
}
}
Rankings::List Eviction::GetListForEntry(EntryImpl* entry) {
return Rankings::NO_USE;
}
bool Eviction::EvictEntry(CacheRankingsBlock* node, bool empty) {
EntryImpl* entry = backend_->GetEnumeratedEntry(node);
if (!entry) {
Trace("NewEntry failed on Trim 0x%x", node->address().value());
return false;
}
ReportTrimTimes(entry);
if (empty || !new_eviction_) {
entry->DoomImpl();
} else {
entry->DeleteEntryData(false);
EntryStore* info = entry->entry()->Data();
DCHECK_EQ(ENTRY_NORMAL, info->state);
rankings_->Remove(entry->rankings(), GetListForEntryV2(entry));
info->state = ENTRY_EVICTED;
entry->entry()->Store();
rankings_->Insert(entry->rankings(), true, Rankings::DELETED);
backend_->OnEvent(Stats::TRIM_ENTRY);
}
entry->Release();
return true;
}
// -----------------------------------------------------------------------
void Eviction::TrimCacheV2(bool empty) {
Trace("*** Trim Cache ***");
trimming_ = true;
TimeTicks start = TimeTicks::Now();
const int kListsToSearch = 3;
Rankings::ScopedRankingsBlock next[kListsToSearch];
int list = Rankings::LAST_ELEMENT;
// Get a node from each list.
for (int i = 0; i < kListsToSearch; i++) {
bool done = false;
next[i].set_rankings(rankings_);
if (done)
continue;
next[i].reset(rankings_->GetPrev(NULL, static_cast<Rankings::List>(i)));
if (!empty && NodeIsOldEnough(next[i].get(), i)) {
list = static_cast<Rankings::List>(i);
done = true;
}
}
// If we are not meeting the time targets lets move on to list length.
if (!empty && Rankings::LAST_ELEMENT == list)
list = SelectListByLength(next);
if (empty)
list = 0;
Rankings::ScopedRankingsBlock node(rankings_);
int target_size = empty ? 0 : max_size_;
for (; list < kListsToSearch; list++) {
while ((header_->num_bytes > target_size && next[list].get()) ||
test_mode_) {
// The iterator could be invalidated within EvictEntry().
if (!next[list]->HasData())
break;
node.reset(next[list].release());
next[list].reset(rankings_->GetPrev(node.get(),
static_cast<Rankings::List>(list)));
if (node->Data()->dirty != backend_->GetCurrentEntryId() || empty) {
// This entry is not being used by anybody.
// Do NOT use node as an iterator after this point.
rankings_->TrackRankingsBlock(node.get(), false);
if (!EvictEntry(node.get(), empty) && !test_mode_)
continue;
if (!empty && test_mode_)
break;
if (!empty && (TimeTicks::Now() - start).InMilliseconds() > 20) {
MessageLoop::current()->PostTask(FROM_HERE,
factory_.NewRunnableMethod(&Eviction::TrimCache, false));
break;
}
}
}
if (!empty)
list = kListsToSearch;
}
if (empty) {
TrimDeleted(true);
} else if (header_->lru.sizes[Rankings::DELETED] > header_->num_entries / 4 &&
!test_mode_) {
MessageLoop::current()->PostTask(FROM_HERE,
factory_.NewRunnableMethod(&Eviction::TrimDeleted, empty));
}
if (empty) {
CACHE_UMA(AGE_MS, "TotalClearTimeV2", 0, start);
} else {
CACHE_UMA(AGE_MS, "TotalTrimTimeV2", backend_->GetSizeGroup(), start);
}
Trace("*** Trim Cache end ***");
trimming_ = false;
return;
}
void Eviction::UpdateRankV2(EntryImpl* entry, bool modified) {
rankings_->UpdateRank(entry->rankings(), modified, GetListForEntryV2(entry));
}
void Eviction::OnOpenEntryV2(EntryImpl* entry) {
EntryStore* info = entry->entry()->Data();
DCHECK_EQ(ENTRY_NORMAL, info->state);
if (info->reuse_count < kint32max) {
info->reuse_count++;
entry->entry()->set_modified();
// We may need to move this to a new list.
if (1 == info->reuse_count) {
rankings_->Remove(entry->rankings(), Rankings::NO_USE);
rankings_->Insert(entry->rankings(), false, Rankings::LOW_USE);
entry->entry()->Store();
} else if (kHighUse == info->reuse_count) {
rankings_->Remove(entry->rankings(), Rankings::LOW_USE);
rankings_->Insert(entry->rankings(), false, Rankings::HIGH_USE);
entry->entry()->Store();
}
}
}
void Eviction::OnCreateEntryV2(EntryImpl* entry) {
EntryStore* info = entry->entry()->Data();
switch (info->state) {
case ENTRY_NORMAL: {
DCHECK(!info->reuse_count);
DCHECK(!info->refetch_count);
break;
};
case ENTRY_EVICTED: {
if (info->refetch_count < kint32max)
info->refetch_count++;
if (info->refetch_count > kHighUse && info->reuse_count < kHighUse) {
info->reuse_count = kHighUse;
} else {
info->reuse_count++;
}
info->state = ENTRY_NORMAL;
entry->entry()->Store();
rankings_->Remove(entry->rankings(), Rankings::DELETED);
break;
};
default:
NOTREACHED();
}
rankings_->Insert(entry->rankings(), true, GetListForEntryV2(entry));
}
void Eviction::OnDoomEntryV2(EntryImpl* entry) {
EntryStore* info = entry->entry()->Data();
if (ENTRY_NORMAL != info->state)
return;
rankings_->Remove(entry->rankings(), GetListForEntryV2(entry));
info->state = ENTRY_DOOMED;
entry->entry()->Store();
rankings_->Insert(entry->rankings(), true, Rankings::DELETED);
}
void Eviction::OnDestroyEntryV2(EntryImpl* entry) {
rankings_->Remove(entry->rankings(), Rankings::DELETED);
}
Rankings::List Eviction::GetListForEntryV2(EntryImpl* entry) {
EntryStore* info = entry->entry()->Data();
DCHECK_EQ(ENTRY_NORMAL, info->state);
if (!info->reuse_count)
return Rankings::NO_USE;
if (info->reuse_count < kHighUse)
return Rankings::LOW_USE;
return Rankings::HIGH_USE;
}
// This is a minimal implementation that just discards the oldest nodes.
// TODO(rvargas): Do something better here.
void Eviction::TrimDeleted(bool empty) {
Trace("*** Trim Deleted ***");
if (backend_->disabled_)
return;
TimeTicks start = TimeTicks::Now();
Rankings::ScopedRankingsBlock node(rankings_);
Rankings::ScopedRankingsBlock next(rankings_,
rankings_->GetPrev(node.get(), Rankings::DELETED));
bool deleted = false;
for (int i = 0; (i < 4 || empty) && next.get(); i++) {
node.reset(next.release());
next.reset(rankings_->GetPrev(node.get(), Rankings::DELETED));
deleted |= RemoveDeletedNode(node.get());
if (test_mode_)
break;
}
// Normally we use 25% for each list. The experiment doubles the number of
// deleted entries, so the total number of entries increases by 25%. Using
// 40% of that value for deleted entries leaves the size of the other three
// lists intact.
int max_length = in_experiment_ ? header_->num_entries * 2 / 5 :
header_->num_entries / 4;
if (deleted && !empty && !test_mode_ &&
header_->lru.sizes[Rankings::DELETED] > max_length) {
MessageLoop::current()->PostTask(FROM_HERE,
factory_.NewRunnableMethod(&Eviction::TrimDeleted, false));
}
CACHE_UMA(AGE_MS, "TotalTrimDeletedTime", 0, start);
Trace("*** Trim Deleted end ***");
return;
}
bool Eviction::RemoveDeletedNode(CacheRankingsBlock* node) {
EntryImpl* entry = backend_->GetEnumeratedEntry(node);
if (!entry) {
Trace("NewEntry failed on Trim 0x%x", node->address().value());
return false;
}
bool doomed = (entry->entry()->Data()->state == ENTRY_DOOMED);
entry->entry()->Data()->state = ENTRY_DOOMED;
entry->DoomImpl();
entry->Release();
return !doomed;
}
bool Eviction::NodeIsOldEnough(CacheRankingsBlock* node, int list) {
if (!node)
return false;
// If possible, we want to keep entries on each list at least kTargetTime
// hours. Each successive list on the enumeration has 2x the target time of
// the previous list.
Time used = Time::FromInternalValue(node->Data()->last_used);
int multiplier = 1 << list;
return (Time::Now() - used).InHours() > kTargetTime * multiplier;
}
int Eviction::SelectListByLength(Rankings::ScopedRankingsBlock* next) {
int data_entries = header_->num_entries -
header_->lru.sizes[Rankings::DELETED];
// Start by having each list to be roughly the same size.
if (header_->lru.sizes[0] > data_entries / 3)
return 0;
int list = (header_->lru.sizes[1] > data_entries / 3) ? 1 : 2;
// Make sure that frequently used items are kept for a minimum time; we know
// that this entry is not older than its current target, but it must be at
// least older than the target for list 0 (kTargetTime), as long as we don't
// exhaust list 0.
if (!NodeIsOldEnough(next[list].get(), 0) &&
header_->lru.sizes[0] > data_entries / 10)
list = 0;
return list;
}
void Eviction::ReportListStats() {
if (!new_eviction_)
return;
Rankings::ScopedRankingsBlock last1(rankings_,
rankings_->GetPrev(NULL, Rankings::NO_USE));
Rankings::ScopedRankingsBlock last2(rankings_,
rankings_->GetPrev(NULL, Rankings::LOW_USE));
Rankings::ScopedRankingsBlock last3(rankings_,
rankings_->GetPrev(NULL, Rankings::HIGH_USE));
Rankings::ScopedRankingsBlock last4(rankings_,
rankings_->GetPrev(NULL, Rankings::DELETED));
if (last1.get())
CACHE_UMA(AGE, "NoUseAge", 0,
Time::FromInternalValue(last1.get()->Data()->last_used));
if (last2.get())
CACHE_UMA(AGE, "LowUseAge", 0,
Time::FromInternalValue(last2.get()->Data()->last_used));
if (last3.get())
CACHE_UMA(AGE, "HighUseAge", 0,
Time::FromInternalValue(last3.get()->Data()->last_used));
if (last4.get())
CACHE_UMA(AGE, "DeletedAge", 0,
Time::FromInternalValue(last4.get()->Data()->last_used));
}
} // namespace disk_cache