You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 
rocksdb/cache/fast_lru_cache.cc

511 lines
15 KiB

// 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/fast_lru_cache.h"
#include <cassert>
#include <cstdint>
#include <cstdio>
#include "monitoring/perf_context_imp.h"
#include "monitoring/statistics.h"
#include "port/lang.h"
#include "util/mutexlock.h"
namespace ROCKSDB_NAMESPACE {
namespace fast_lru_cache {
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,
CacheMetadataChargePolicy metadata_charge_policy,
int max_upper_hash_bits)
: capacity_(0),
strict_capacity_limit_(strict_capacity_limit),
table_(max_upper_hash_bits),
usage_(0),
lru_usage_(0) {
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);
}
}
// Free the entries here outside of mutex for performance reasons.
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::LRU_Remove(LRUHandle* e) {
assert(e->next != nullptr);
assert(e->prev != nullptr);
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;
}
void LRUCacheShard::LRU_Insert(LRUHandle* e) {
assert(e->next == nullptr);
assert(e->prev == nullptr);
size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_);
// Inset "e" to head of LRU list.
e->next = &lru_;
e->prev = lru_.prev;
e->prev->next = e;
e->next->prev = e;
lru_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;
EvictFromLRU(0, &last_reference_list);
}
// Free the entries here 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;
}
Status LRUCacheShard::InsertItem(LRUHandle* e, Cache::Handle** handle,
bool free_handle_on_fail) {
Status s = Status::OK();
autovector<LRUHandle*> last_reference_list;
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)) {
e->SetInCache(false);
if (handle == nullptr) {
// Don't insert the entry but still return ok, as if the entry inserted
// into cache and get evicted immediately.
last_reference_list.push_back(e);
} else {
if (free_handle_on_fail) {
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 {
// If caller already holds a ref, no need to take one here.
if (!e->HasRefs()) {
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;
}
Cache::Handle* LRUCacheShard::Lookup(const Slice& key, uint32_t hash) {
LRUHandle* e = nullptr;
{
MutexLock l(&mutex_);
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();
}
}
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;
}
bool LRUCacheShard::Release(Cache::Handle* handle, bool erase_if_last_ref) {
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_ || erase_if_last_ref) {
// The LRU list must be empty since the cache is full.
assert(lru_.next == &lru_ || erase_if_last_ref);
// 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 it was the last reference, then decrement the cache usage.
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, Cache::DeleterFn deleter,
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()]);
e->value = value;
e->flags = 0;
e->deleter = deleter;
e->charge = charge;
e->key_length = key.size();
e->hash = hash;
e->refs = 0;
e->next = e->prev = nullptr;
e->SetInCache(true);
memcpy(e->key_data, key.data(), key.size());
return InsertItem(e, handle, /* free_handle_on_fail */ true);
}
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 { return std::string{}; }
LRUCache::LRUCache(size_t capacity, int num_shard_bits,
bool strict_capacity_limit,
CacheMetadataChargePolicy metadata_charge_policy)
: ShardedCache(capacity, num_shard_bits, strict_capacity_limit) {
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, 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;
}
Cache::DeleterFn LRUCache::GetDeleter(Handle* handle) const {
auto h = reinterpret_cast<const LRUHandle*>(handle);
return h->deleter;
}
uint32_t LRUCache::GetHash(Handle* handle) const {
return reinterpret_cast<const LRUHandle*>(handle)->hash;
}
void LRUCache::DisownData() {
// Leak data only if that won't generate an ASAN/valgrind warning.
if (!kMustFreeHeapAllocations) {
shards_ = nullptr;
num_shards_ = 0;
}
}
} // namespace fast_lru_cache
std::shared_ptr<Cache> NewFastLRUCache(
size_t capacity, int num_shard_bits, bool strict_capacity_limit,
CacheMetadataChargePolicy metadata_charge_policy) {
if (num_shard_bits >= 20) {
return nullptr; // The cache cannot be sharded into too many fine pieces.
}
if (num_shard_bits < 0) {
num_shard_bits = GetDefaultCacheShardBits(capacity);
}
return std::make_shared<fast_lru_cache::LRUCache>(
capacity, num_shard_bits, strict_capacity_limit, metadata_charge_policy);
}
} // namespace ROCKSDB_NAMESPACE