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rocksdb/cache/lru_cache.cc

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "cache/lru_cache.h"
#include <cassert>
#include <cstdint>
#include <cstdio>
#include "util/mutexlock.h"
namespace ROCKSDB_NAMESPACE {
LRUHandleTable::LRUHandleTable(int max_upper_hash_bits)
: length_bits_(/* historical starting size*/ 4),
list_(new LRUHandle* [size_t{1} << length_bits_] {}),
elems_(0),
max_length_bits_(max_upper_hash_bits) {}
LRUHandleTable::~LRUHandleTable() {
ApplyToEntriesRange(
[](LRUHandle* h) {
if (!h->HasRefs()) {
h->Free();
}
},
0, uint32_t{1} << length_bits_);
}
LRUHandle* LRUHandleTable::Lookup(const Slice& key, uint32_t hash) {
return *FindPointer(key, hash);
}
LRUHandle* LRUHandleTable::Insert(LRUHandle* h) {
LRUHandle** ptr = FindPointer(h->key(), h->hash);
LRUHandle* old = *ptr;
h->next_hash = (old == nullptr ? nullptr : old->next_hash);
*ptr = h;
if (old == nullptr) {
++elems_;
if ((elems_ >> length_bits_) > 0) { // elems_ >= length
// Since each cache entry is fairly large, we aim for a small
// average linked list length (<= 1).
Resize();
}
}
return old;
}
LRUHandle* LRUHandleTable::Remove(const Slice& key, uint32_t hash) {
LRUHandle** ptr = FindPointer(key, hash);
LRUHandle* result = *ptr;
if (result != nullptr) {
*ptr = result->next_hash;
--elems_;
}
return result;
}
LRUHandle** LRUHandleTable::FindPointer(const Slice& key, uint32_t hash) {
LRUHandle** ptr = &list_[hash >> (32 - length_bits_)];
while (*ptr != nullptr && ((*ptr)->hash != hash || key != (*ptr)->key())) {
ptr = &(*ptr)->next_hash;
}
return ptr;
}
void LRUHandleTable::Resize() {
if (length_bits_ >= max_length_bits_) {
// Due to reaching limit of hash information, if we made the table
// bigger, we would allocate more addresses but only the same
// number would be used.
return;
}
if (length_bits_ >= 31) {
// Avoid undefined behavior shifting uint32_t by 32
return;
}
uint32_t old_length = uint32_t{1} << length_bits_;
int new_length_bits = length_bits_ + 1;
std::unique_ptr<LRUHandle* []> new_list {
new LRUHandle* [size_t{1} << new_length_bits] {}
};
uint32_t count = 0;
for (uint32_t i = 0; i < old_length; i++) {
LRUHandle* h = list_[i];
while (h != nullptr) {
LRUHandle* next = h->next_hash;
uint32_t hash = h->hash;
LRUHandle** ptr = &new_list[hash >> (32 - new_length_bits)];
h->next_hash = *ptr;
*ptr = h;
h = next;
count++;
}
}
assert(elems_ == count);
list_ = std::move(new_list);
length_bits_ = new_length_bits;
}
LRUCacheShard::LRUCacheShard(size_t capacity, bool strict_capacity_limit,
double high_pri_pool_ratio,
bool use_adaptive_mutex,
CacheMetadataChargePolicy metadata_charge_policy,
int max_upper_hash_bits)
: capacity_(0),
high_pri_pool_usage_(0),
strict_capacity_limit_(strict_capacity_limit),
high_pri_pool_ratio_(high_pri_pool_ratio),
high_pri_pool_capacity_(0),
table_(max_upper_hash_bits),
usage_(0),
lru_usage_(0),
mutex_(use_adaptive_mutex) {
set_metadata_charge_policy(metadata_charge_policy);
// Make empty circular linked list
lru_.next = &lru_;
lru_.prev = &lru_;
lru_low_pri_ = &lru_;
SetCapacity(capacity);
}
void LRUCacheShard::EraseUnRefEntries() {
autovector<LRUHandle*> last_reference_list;
{
MutexLock l(&mutex_);
while (lru_.next != &lru_) {
LRUHandle* old = lru_.next;
// LRU list contains only elements which can be evicted
assert(old->InCache() && !old->HasRefs());
LRU_Remove(old);
table_.Remove(old->key(), old->hash);
old->SetInCache(false);
size_t total_charge = old->CalcTotalCharge(metadata_charge_policy_);
assert(usage_ >= total_charge);
usage_ -= total_charge;
last_reference_list.push_back(old);
}
}
for (auto entry : last_reference_list) {
entry->Free();
}
}
void LRUCacheShard::ApplyToSomeEntries(
const std::function<void(const Slice& key, void* value, size_t charge,
DeleterFn deleter)>& callback,
uint32_t average_entries_per_lock, uint32_t* state) {
// The state is essentially going to be the starting hash, which works
// nicely even if we resize between calls because we use upper-most
// hash bits for table indexes.
MutexLock l(&mutex_);
uint32_t length_bits = table_.GetLengthBits();
uint32_t length = uint32_t{1} << length_bits;
assert(average_entries_per_lock > 0);
// Assuming we are called with same average_entries_per_lock repeatedly,
// this simplifies some logic (index_end will not overflow)
assert(average_entries_per_lock < length || *state == 0);
uint32_t index_begin = *state >> (32 - length_bits);
uint32_t index_end = index_begin + average_entries_per_lock;
if (index_end >= length) {
// Going to end
index_end = length;
*state = UINT32_MAX;
} else {
*state = index_end << (32 - length_bits);
}
table_.ApplyToEntriesRange(
[callback](LRUHandle* h) {
callback(h->key(), h->value, h->charge, h->deleter);
},
index_begin, index_end);
}
void LRUCacheShard::TEST_GetLRUList(LRUHandle** lru, LRUHandle** lru_low_pri) {
MutexLock l(&mutex_);
*lru = &lru_;
*lru_low_pri = lru_low_pri_;
}
size_t LRUCacheShard::TEST_GetLRUSize() {
MutexLock l(&mutex_);
LRUHandle* lru_handle = lru_.next;
size_t lru_size = 0;
while (lru_handle != &lru_) {
lru_size++;
lru_handle = lru_handle->next;
}
return lru_size;
}
double LRUCacheShard::GetHighPriPoolRatio() {
MutexLock l(&mutex_);
return high_pri_pool_ratio_;
}
void LRUCacheShard::LRU_Remove(LRUHandle* e) {
assert(e->next != nullptr);
assert(e->prev != nullptr);
if (lru_low_pri_ == e) {
lru_low_pri_ = e->prev;
}
e->next->prev = e->prev;
e->prev->next = e->next;
e->prev = e->next = nullptr;
size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_);
assert(lru_usage_ >= total_charge);
lru_usage_ -= total_charge;
if (e->InHighPriPool()) {
assert(high_pri_pool_usage_ >= total_charge);
high_pri_pool_usage_ -= total_charge;
}
}
void LRUCacheShard::LRU_Insert(LRUHandle* e) {
assert(e->next == nullptr);
assert(e->prev == nullptr);
size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_);
if (high_pri_pool_ratio_ > 0 && (e->IsHighPri() || e->HasHit())) {
// Inset "e" to head of LRU list.
e->next = &lru_;
e->prev = lru_.prev;
e->prev->next = e;
e->next->prev = e;
e->SetInHighPriPool(true);
high_pri_pool_usage_ += total_charge;
MaintainPoolSize();
} else {
// Insert "e" to the head of low-pri pool. Note that when
// high_pri_pool_ratio is 0, head of low-pri pool is also head of LRU list.
e->next = lru_low_pri_->next;
e->prev = lru_low_pri_;
e->prev->next = e;
e->next->prev = e;
e->SetInHighPriPool(false);
lru_low_pri_ = e;
}
lru_usage_ += total_charge;
}
void LRUCacheShard::MaintainPoolSize() {
while (high_pri_pool_usage_ > high_pri_pool_capacity_) {
// Overflow last entry in high-pri pool to low-pri pool.
lru_low_pri_ = lru_low_pri_->next;
assert(lru_low_pri_ != &lru_);
lru_low_pri_->SetInHighPriPool(false);
size_t total_charge =
lru_low_pri_->CalcTotalCharge(metadata_charge_policy_);
assert(high_pri_pool_usage_ >= total_charge);
high_pri_pool_usage_ -= total_charge;
}
}
void LRUCacheShard::EvictFromLRU(size_t charge,
autovector<LRUHandle*>* deleted) {
while ((usage_ + charge) > capacity_ && lru_.next != &lru_) {
LRUHandle* old = lru_.next;
// LRU list contains only elements which can be evicted
assert(old->InCache() && !old->HasRefs());
LRU_Remove(old);
table_.Remove(old->key(), old->hash);
old->SetInCache(false);
size_t old_total_charge = old->CalcTotalCharge(metadata_charge_policy_);
assert(usage_ >= old_total_charge);
usage_ -= old_total_charge;
deleted->push_back(old);
}
}
void LRUCacheShard::SetCapacity(size_t capacity) {
autovector<LRUHandle*> last_reference_list;
{
MutexLock l(&mutex_);
capacity_ = capacity;
high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;
EvictFromLRU(0, &last_reference_list);
}
// Free the entries outside of mutex for performance reasons
for (auto entry : last_reference_list) {
entry->Free();
}
}
void LRUCacheShard::SetStrictCapacityLimit(bool strict_capacity_limit) {
MutexLock l(&mutex_);
strict_capacity_limit_ = strict_capacity_limit;
}
Cache::Handle* LRUCacheShard::Lookup(const Slice& key, uint32_t hash) {
MutexLock l(&mutex_);
LRUHandle* e = table_.Lookup(key, hash);
if (e != nullptr) {
assert(e->InCache());
if (!e->HasRefs()) {
// The entry is in LRU since it's in hash and has no external references
LRU_Remove(e);
}
e->Ref();
e->SetHit();
}
return reinterpret_cast<Cache::Handle*>(e);
}
bool LRUCacheShard::Ref(Cache::Handle* h) {
LRUHandle* e = reinterpret_cast<LRUHandle*>(h);
MutexLock l(&mutex_);
// To create another reference - entry must be already externally referenced
assert(e->HasRefs());
e->Ref();
return true;
}
void LRUCacheShard::SetHighPriorityPoolRatio(double high_pri_pool_ratio) {
MutexLock l(&mutex_);
high_pri_pool_ratio_ = high_pri_pool_ratio;
high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;
MaintainPoolSize();
}
bool LRUCacheShard::Release(Cache::Handle* handle, bool force_erase) {
if (handle == nullptr) {
return false;
}
LRUHandle* e = reinterpret_cast<LRUHandle*>(handle);
bool last_reference = false;
{
MutexLock l(&mutex_);
last_reference = e->Unref();
if (last_reference && e->InCache()) {
// The item is still in cache, and nobody else holds a reference to it
if (usage_ > capacity_ || force_erase) {
// The LRU list must be empty since the cache is full
assert(lru_.next == &lru_ || force_erase);
// Take this opportunity and remove the item
table_.Remove(e->key(), e->hash);
e->SetInCache(false);
} else {
// Put the item back on the LRU list, and don't free it
LRU_Insert(e);
last_reference = false;
}
}
if (last_reference) {
size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_);
assert(usage_ >= total_charge);
usage_ -= total_charge;
}
}
// Free the entry here outside of mutex for performance reasons
if (last_reference) {
e->Free();
}
return last_reference;
}
Status LRUCacheShard::Insert(const Slice& key, uint32_t hash, void* value,
size_t charge,
void (*deleter)(const Slice& key, void* value),
Cache::Handle** handle, Cache::Priority priority) {
// Allocate the memory here outside of the mutex
// If the cache is full, we'll have to release it
// It shouldn't happen very often though.
LRUHandle* e = reinterpret_cast<LRUHandle*>(
new char[sizeof(LRUHandle) - 1 + key.size()]);
Status s = Status::OK();
autovector<LRUHandle*> last_reference_list;
e->value = value;
e->deleter = deleter;
e->charge = charge;
e->key_length = key.size();
e->flags = 0;
e->hash = hash;
e->refs = 0;
e->next = e->prev = nullptr;
e->SetInCache(true);
e->SetPriority(priority);
memcpy(e->key_data, key.data(), key.size());
size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_);
{
MutexLock l(&mutex_);
// Free the space following strict LRU policy until enough space
// is freed or the lru list is empty
EvictFromLRU(total_charge, &last_reference_list);
if ((usage_ + total_charge) > capacity_ &&
(strict_capacity_limit_ || handle == nullptr)) {
if (handle == nullptr) {
// Don't insert the entry but still return ok, as if the entry inserted
// into cache and get evicted immediately.
e->SetInCache(false);
last_reference_list.push_back(e);
} else {
delete[] reinterpret_cast<char*>(e);
*handle = nullptr;
s = Status::Incomplete("Insert failed due to LRU cache being full.");
}
} else {
// Insert into the cache. Note that the cache might get larger than its
// capacity if not enough space was freed up.
LRUHandle* old = table_.Insert(e);
usage_ += total_charge;
if (old != nullptr) {
s = Status::OkOverwritten();
assert(old->InCache());
old->SetInCache(false);
if (!old->HasRefs()) {
// old is on LRU because it's in cache and its reference count is 0
LRU_Remove(old);
size_t old_total_charge =
old->CalcTotalCharge(metadata_charge_policy_);
assert(usage_ >= old_total_charge);
usage_ -= old_total_charge;
last_reference_list.push_back(old);
}
}
if (handle == nullptr) {
LRU_Insert(e);
} else {
e->Ref();
*handle = reinterpret_cast<Cache::Handle*>(e);
}
}
}
// Free the entries here outside of mutex for performance reasons
for (auto entry : last_reference_list) {
entry->Free();
}
return s;
}
void LRUCacheShard::Erase(const Slice& key, uint32_t hash) {
LRUHandle* e;
bool last_reference = false;
{
MutexLock l(&mutex_);
e = table_.Remove(key, hash);
if (e != nullptr) {
assert(e->InCache());
e->SetInCache(false);
if (!e->HasRefs()) {
// The entry is in LRU since it's in hash and has no external references
LRU_Remove(e);
size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_);
assert(usage_ >= total_charge);
usage_ -= total_charge;
last_reference = true;
}
}
}
// Free the entry here outside of mutex for performance reasons
// last_reference will only be true if e != nullptr
if (last_reference) {
e->Free();
}
}
size_t LRUCacheShard::GetUsage() const {
MutexLock l(&mutex_);
return usage_;
}
size_t LRUCacheShard::GetPinnedUsage() const {
MutexLock l(&mutex_);
assert(usage_ >= lru_usage_);
return usage_ - lru_usage_;
}
std::string LRUCacheShard::GetPrintableOptions() const {
const int kBufferSize = 200;
char buffer[kBufferSize];
{
MutexLock l(&mutex_);
snprintf(buffer, kBufferSize, " high_pri_pool_ratio: %.3lf\n",
high_pri_pool_ratio_);
}
return std::string(buffer);
}
LRUCache::LRUCache(size_t capacity, int num_shard_bits,
bool strict_capacity_limit, double high_pri_pool_ratio,
std::shared_ptr<MemoryAllocator> allocator,
bool use_adaptive_mutex,
CacheMetadataChargePolicy metadata_charge_policy)
: ShardedCache(capacity, num_shard_bits, strict_capacity_limit,
std::move(allocator)) {
num_shards_ = 1 << num_shard_bits;
shards_ = reinterpret_cast<LRUCacheShard*>(
port::cacheline_aligned_alloc(sizeof(LRUCacheShard) * num_shards_));
size_t per_shard = (capacity + (num_shards_ - 1)) / num_shards_;
for (int i = 0; i < num_shards_; i++) {
new (&shards_[i])
LRUCacheShard(per_shard, strict_capacity_limit, high_pri_pool_ratio,
use_adaptive_mutex, metadata_charge_policy,
/* max_upper_hash_bits */ 32 - num_shard_bits);
}
}
LRUCache::~LRUCache() {
if (shards_ != nullptr) {
assert(num_shards_ > 0);
for (int i = 0; i < num_shards_; i++) {
shards_[i].~LRUCacheShard();
}
port::cacheline_aligned_free(shards_);
}
}
CacheShard* LRUCache::GetShard(uint32_t shard) {
return reinterpret_cast<CacheShard*>(&shards_[shard]);
}
const CacheShard* LRUCache::GetShard(uint32_t shard) const {
return reinterpret_cast<CacheShard*>(&shards_[shard]);
}
void* LRUCache::Value(Handle* handle) {
return reinterpret_cast<const LRUHandle*>(handle)->value;
}
size_t LRUCache::GetCharge(Handle* handle) const {
return reinterpret_cast<const LRUHandle*>(handle)->charge;
}
uint32_t LRUCache::GetHash(Handle* handle) const {
return reinterpret_cast<const LRUHandle*>(handle)->hash;
}
void LRUCache::DisownData() {
// Do not drop data if compile with ASAN to suppress leak warning.
#if defined(__clang__)
#if !defined(__has_feature) || !__has_feature(address_sanitizer)
shards_ = nullptr;
num_shards_ = 0;
#endif
#else // __clang__
#ifndef __SANITIZE_ADDRESS__
shards_ = nullptr;
num_shards_ = 0;
#endif // !__SANITIZE_ADDRESS__
#endif // __clang__
}
size_t LRUCache::TEST_GetLRUSize() {
size_t lru_size_of_all_shards = 0;
for (int i = 0; i < num_shards_; i++) {
lru_size_of_all_shards += shards_[i].TEST_GetLRUSize();
}
return lru_size_of_all_shards;
}
double LRUCache::GetHighPriPoolRatio() {
double result = 0.0;
if (num_shards_ > 0) {
result = shards_[0].GetHighPriPoolRatio();
}
return result;
}
std::shared_ptr<Cache> NewLRUCache(const LRUCacheOptions& cache_opts) {
return NewLRUCache(cache_opts.capacity, cache_opts.num_shard_bits,
cache_opts.strict_capacity_limit,
cache_opts.high_pri_pool_ratio,
cache_opts.memory_allocator, cache_opts.use_adaptive_mutex,
cache_opts.metadata_charge_policy);
}
std::shared_ptr<Cache> NewLRUCache(
size_t capacity, int num_shard_bits, bool strict_capacity_limit,
double high_pri_pool_ratio,
std::shared_ptr<MemoryAllocator> memory_allocator, bool use_adaptive_mutex,
CacheMetadataChargePolicy metadata_charge_policy) {
if (num_shard_bits >= 20) {
return nullptr; // the cache cannot be sharded into too many fine pieces
}
if (high_pri_pool_ratio < 0.0 || high_pri_pool_ratio > 1.0) {
// invalid high_pri_pool_ratio
return nullptr;
}
if (num_shard_bits < 0) {
num_shard_bits = GetDefaultCacheShardBits(capacity);
}
return std::make_shared<LRUCache>(
capacity, num_shard_bits, strict_capacity_limit, high_pri_pool_ratio,
std::move(memory_allocator), use_adaptive_mutex, metadata_charge_policy);
}
} // namespace ROCKSDB_NAMESPACE