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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 <cstdlib>
#include "cache/secondary_cache_adapter.h"
#include "monitoring/perf_context_imp.h"
#include "monitoring/statistics_impl.h"
#include "port/lang.h"
#include "util/distributed_mutex.h"
namespace ROCKSDB_NAMESPACE {
namespace lru_cache {
LRUHandleTable::LRUHandleTable(int max_upper_hash_bits,
MemoryAllocator* allocator)
: length_bits_(/* historical starting size*/ 4),
list_(new LRUHandle* [size_t{1} << length_bits_] {}),
elems_(0),
max_length_bits_(max_upper_hash_bits),
allocator_(allocator) {}
LRUHandleTable::~LRUHandleTable() {
auto alloc = allocator_;
ApplyToEntriesRange(
[alloc](LRUHandle* h) {
if (!h->HasRefs()) {
h->Free(alloc);
}
},
0, size_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] {}
};
[[maybe_unused]] 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,
double low_pri_pool_ratio, bool use_adaptive_mutex,
CacheMetadataChargePolicy metadata_charge_policy,
int max_upper_hash_bits,
MemoryAllocator* allocator,
const Cache::EvictionCallback* eviction_callback)
: CacheShardBase(metadata_charge_policy),
capacity_(0),
high_pri_pool_usage_(0),
low_pri_pool_usage_(0),
strict_capacity_limit_(strict_capacity_limit),
high_pri_pool_ratio_(high_pri_pool_ratio),
high_pri_pool_capacity_(0),
low_pri_pool_ratio_(low_pri_pool_ratio),
low_pri_pool_capacity_(0),
table_(max_upper_hash_bits, allocator),
usage_(0),
lru_usage_(0),
mutex_(use_adaptive_mutex),
eviction_callback_(*eviction_callback) {
// Make empty circular linked list.
lru_.next = &lru_;
lru_.prev = &lru_;
lru_low_pri_ = &lru_;
lru_bottom_pri_ = &lru_;
SetCapacity(capacity);
}
void LRUCacheShard::EraseUnRefEntries() {
autovector<LRUHandle*> last_reference_list;
{
DMutexLock 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);
assert(usage_ >= old->total_charge);
usage_ -= old->total_charge;
last_reference_list.push_back(old);
}
}
for (auto entry : last_reference_list) {
entry->Free(table_.GetAllocator());
}
}
void LRUCacheShard::ApplyToSomeEntries(
const std::function<void(const Slice& key, Cache::ObjectPtr value,
size_t charge,
const Cache::CacheItemHelper* helper)>& callback,
size_t average_entries_per_lock, size_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.
DMutexLock l(mutex_);
int length_bits = table_.GetLengthBits();
size_t length = size_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);
size_t index_begin = *state >> (sizeof(size_t) * 8u - length_bits);
size_t index_end = index_begin + average_entries_per_lock;
if (index_end >= length) {
// Going to end
index_end = length;
*state = SIZE_MAX;
} else {
*state = index_end << (sizeof(size_t) * 8u - length_bits);
}
table_.ApplyToEntriesRange(
[callback,
metadata_charge_policy = metadata_charge_policy_](LRUHandle* h) {
callback(h->key(), h->value, h->GetCharge(metadata_charge_policy),
h->helper);
},
index_begin, index_end);
}
void LRUCacheShard::TEST_GetLRUList(LRUHandle** lru, LRUHandle** lru_low_pri,
LRUHandle** lru_bottom_pri) {
DMutexLock l(mutex_);
*lru = &lru_;
*lru_low_pri = lru_low_pri_;
*lru_bottom_pri = lru_bottom_pri_;
}
size_t LRUCacheShard::TEST_GetLRUSize() {
DMutexLock 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() {
DMutexLock l(mutex_);
return high_pri_pool_ratio_;
}
double LRUCacheShard::GetLowPriPoolRatio() {
DMutexLock l(mutex_);
return low_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;
}
if (lru_bottom_pri_ == e) {
lru_bottom_pri_ = e->prev;
}
e->next->prev = e->prev;
e->prev->next = e->next;
e->prev = e->next = nullptr;
assert(lru_usage_ >= e->total_charge);
lru_usage_ -= e->total_charge;
assert(!e->InHighPriPool() || !e->InLowPriPool());
if (e->InHighPriPool()) {
assert(high_pri_pool_usage_ >= e->total_charge);
high_pri_pool_usage_ -= e->total_charge;
} else if (e->InLowPriPool()) {
assert(low_pri_pool_usage_ >= e->total_charge);
low_pri_pool_usage_ -= e->total_charge;
}
}
void LRUCacheShard::LRU_Insert(LRUHandle* e) {
assert(e->next == nullptr);
assert(e->prev == nullptr);
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);
e->SetInLowPriPool(false);
high_pri_pool_usage_ += e->total_charge;
MaintainPoolSize();
} else if (low_pri_pool_ratio_ > 0 &&
(e->IsHighPri() || e->IsLowPri() || e->HasHit())) {
// Insert "e" to the head of low-pri pool.
e->next = lru_low_pri_->next;
e->prev = lru_low_pri_;
e->prev->next = e;
e->next->prev = e;
e->SetInHighPriPool(false);
e->SetInLowPriPool(true);
low_pri_pool_usage_ += e->total_charge;
MaintainPoolSize();
lru_low_pri_ = e;
} else {
// Insert "e" to the head of bottom-pri pool.
e->next = lru_bottom_pri_->next;
e->prev = lru_bottom_pri_;
e->prev->next = e;
e->next->prev = e;
e->SetInHighPriPool(false);
e->SetInLowPriPool(false);
// if the low-pri pool is empty, lru_low_pri_ also needs to be updated.
if (lru_bottom_pri_ == lru_low_pri_) {
lru_low_pri_ = e;
}
lru_bottom_pri_ = e;
}
lru_usage_ += e->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);
lru_low_pri_->SetInLowPriPool(true);
assert(high_pri_pool_usage_ >= lru_low_pri_->total_charge);
high_pri_pool_usage_ -= lru_low_pri_->total_charge;
low_pri_pool_usage_ += lru_low_pri_->total_charge;
}
while (low_pri_pool_usage_ > low_pri_pool_capacity_) {
// Overflow last entry in low-pri pool to bottom-pri pool.
lru_bottom_pri_ = lru_bottom_pri_->next;
assert(lru_bottom_pri_ != &lru_);
lru_bottom_pri_->SetInHighPriPool(false);
lru_bottom_pri_->SetInLowPriPool(false);
assert(low_pri_pool_usage_ >= lru_bottom_pri_->total_charge);
low_pri_pool_usage_ -= lru_bottom_pri_->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);
assert(usage_ >= old->total_charge);
usage_ -= old->total_charge;
deleted->push_back(old);
}
}
void LRUCacheShard::NotifyEvicted(
const autovector<LRUHandle*>& evicted_handles) {
MemoryAllocator* alloc = table_.GetAllocator();
for (LRUHandle* entry : evicted_handles) {
if (eviction_callback_ &&
eviction_callback_(entry->key(), static_cast<Cache::Handle*>(entry),
entry->HasHit())) {
// Callback took ownership of obj; just free handle
free(entry);
} else {
// Free the entries here outside of mutex for performance reasons.
entry->Free(alloc);
}
}
}
void LRUCacheShard::SetCapacity(size_t capacity) {
autovector<LRUHandle*> last_reference_list;
{
DMutexLock l(mutex_);
capacity_ = capacity;
high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;
low_pri_pool_capacity_ = capacity_ * low_pri_pool_ratio_;
EvictFromLRU(0, &last_reference_list);
}
NotifyEvicted(last_reference_list);
}
void LRUCacheShard::SetStrictCapacityLimit(bool strict_capacity_limit) {
DMutexLock l(mutex_);
strict_capacity_limit_ = strict_capacity_limit;
}
Status LRUCacheShard::InsertItem(LRUHandle* e, LRUHandle** handle) {
Status s = Status::OK();
autovector<LRUHandle*> last_reference_list;
{
DMutexLock l(mutex_);
// Free the space following strict LRU policy until enough space
// is freed or the lru list is empty.
EvictFromLRU(e->total_charge, &last_reference_list);
if ((usage_ + e->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 {
free(e);
e = nullptr;
*handle = nullptr;
s = Status::MemoryLimit("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_ += e->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);
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 = e;
}
}
}
NotifyEvicted(last_reference_list);
return s;
}
LRUHandle* LRUCacheShard::Lookup(const Slice& key, uint32_t hash,
const Cache::CacheItemHelper* /*helper*/,
Cache::CreateContext* /*create_context*/,
Cache::Priority /*priority*/,
Statistics* /*stats*/) {
DMutexLock 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 e;
}
bool LRUCacheShard::Ref(LRUHandle* e) {
DMutexLock 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) {
DMutexLock l(mutex_);
high_pri_pool_ratio_ = high_pri_pool_ratio;
high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;
MaintainPoolSize();
}
void LRUCacheShard::SetLowPriorityPoolRatio(double low_pri_pool_ratio) {
DMutexLock l(mutex_);
low_pri_pool_ratio_ = low_pri_pool_ratio;
low_pri_pool_capacity_ = capacity_ * low_pri_pool_ratio_;
MaintainPoolSize();
}
bool LRUCacheShard::Release(LRUHandle* e, bool /*useful*/,
bool erase_if_last_ref) {
if (e == nullptr) {
return false;
}
bool must_free;
bool was_in_cache;
{
DMutexLock l(mutex_);
must_free = e->Unref();
was_in_cache = e->InCache();
if (must_free && was_in_cache) {
// 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);
must_free = false;
}
}
// If about to be freed, then decrement the cache usage.
if (must_free) {
assert(usage_ >= e->total_charge);
usage_ -= e->total_charge;
}
}
// Free the entry here outside of mutex for performance reasons.
if (must_free) {
// Only call eviction callback if we're sure no one requested erasure
// FIXME: disabled because of test churn
if (false && was_in_cache && !erase_if_last_ref && eviction_callback_ &&
eviction_callback_(e->key(), static_cast<Cache::Handle*>(e),
e->HasHit())) {
// Callback took ownership of obj; just free handle
free(e);
} else {
e->Free(table_.GetAllocator());
}
}
return must_free;
}
LRUHandle* LRUCacheShard::CreateHandle(const Slice& key, uint32_t hash,
Cache::ObjectPtr value,
const Cache::CacheItemHelper* helper,
size_t charge) {
assert(helper);
// value == nullptr is reserved for indicating failure in SecondaryCache
assert(!(helper->IsSecondaryCacheCompatible() && value == nullptr));
// 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 =
static_cast<LRUHandle*>(malloc(sizeof(LRUHandle) - 1 + key.size()));
e->value = value;
e->m_flags = 0;
e->im_flags = 0;
e->helper = helper;
e->key_length = key.size();
e->hash = hash;
e->refs = 0;
e->next = e->prev = nullptr;
memcpy(e->key_data, key.data(), key.size());
e->CalcTotalCharge(charge, metadata_charge_policy_);
return e;
}
Status LRUCacheShard::Insert(const Slice& key, uint32_t hash,
Cache::ObjectPtr value,
const Cache::CacheItemHelper* helper,
size_t charge, LRUHandle** handle,
Cache::Priority priority) {
LRUHandle* e = CreateHandle(key, hash, value, helper, charge);
e->SetPriority(priority);
e->SetInCache(true);
return InsertItem(e, handle);
}
LRUHandle* LRUCacheShard::CreateStandalone(const Slice& key, uint32_t hash,
Cache::ObjectPtr value,
const Cache::CacheItemHelper* helper,
size_t charge,
bool allow_uncharged) {
LRUHandle* e = CreateHandle(key, hash, value, helper, charge);
e->SetIsStandalone(true);
e->Ref();
autovector<LRUHandle*> last_reference_list;
{
DMutexLock l(mutex_);
EvictFromLRU(e->total_charge, &last_reference_list);
if (strict_capacity_limit_ && (usage_ + e->total_charge) > capacity_) {
if (allow_uncharged) {
e->total_charge = 0;
} else {
free(e);
e = nullptr;
}
} else {
usage_ += e->total_charge;
}
}
NotifyEvicted(last_reference_list);
return e;
}
void LRUCacheShard::Erase(const Slice& key, uint32_t hash) {
LRUHandle* e;
bool last_reference = false;
{
DMutexLock 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);
assert(usage_ >= e->total_charge);
usage_ -= e->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(table_.GetAllocator());
}
}
size_t LRUCacheShard::GetUsage() const {
DMutexLock l(mutex_);
return usage_;
}
size_t LRUCacheShard::GetPinnedUsage() const {
DMutexLock l(mutex_);
assert(usage_ >= lru_usage_);
return usage_ - lru_usage_;
}
size_t LRUCacheShard::GetOccupancyCount() const {
DMutexLock l(mutex_);
return table_.GetOccupancyCount();
}
size_t LRUCacheShard::GetTableAddressCount() const {
DMutexLock l(mutex_);
return size_t{1} << table_.GetLengthBits();
}
void LRUCacheShard::AppendPrintableOptions(std::string& str) const {
const int kBufferSize = 200;
char buffer[kBufferSize];
{
DMutexLock l(mutex_);
snprintf(buffer, kBufferSize, " high_pri_pool_ratio: %.3lf\n",
high_pri_pool_ratio_);
snprintf(buffer + strlen(buffer), kBufferSize - strlen(buffer),
" low_pri_pool_ratio: %.3lf\n", low_pri_pool_ratio_);
}
str.append(buffer);
}
LRUCache::LRUCache(const LRUCacheOptions& opts) : ShardedCache(opts) {
size_t per_shard = GetPerShardCapacity();
MemoryAllocator* alloc = memory_allocator();
InitShards([&](LRUCacheShard* cs) {
new (cs) LRUCacheShard(per_shard, opts.strict_capacity_limit,
opts.high_pri_pool_ratio, opts.low_pri_pool_ratio,
opts.use_adaptive_mutex, opts.metadata_charge_policy,
/* max_upper_hash_bits */ 32 - opts.num_shard_bits,
alloc, &eviction_callback_);
});
}
Cache::ObjectPtr LRUCache::Value(Handle* handle) {
auto h = static_cast<const LRUHandle*>(handle);
return h->value;
}
size_t LRUCache::GetCharge(Handle* handle) const {
return static_cast<const LRUHandle*>(handle)->GetCharge(
GetShard(0).metadata_charge_policy_);
}
const Cache::CacheItemHelper* LRUCache::GetCacheItemHelper(
Handle* handle) const {
auto h = static_cast<const LRUHandle*>(handle);
return h->helper;
}
size_t LRUCache::TEST_GetLRUSize() {
return SumOverShards([](LRUCacheShard& cs) { return cs.TEST_GetLRUSize(); });
}
double LRUCache::GetHighPriPoolRatio() {
return GetShard(0).GetHighPriPoolRatio();
}
} // namespace lru_cache
std::shared_ptr<Cache> LRUCacheOptions::MakeSharedCache() const {
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 (low_pri_pool_ratio < 0.0 || low_pri_pool_ratio > 1.0) {
// Invalid low_pri_pool_ratio
return nullptr;
}
if (low_pri_pool_ratio + high_pri_pool_ratio > 1.0) {
// Invalid high_pri_pool_ratio and low_pri_pool_ratio combination
return nullptr;
}
// For sanitized options
LRUCacheOptions opts = *this;
if (opts.num_shard_bits < 0) {
opts.num_shard_bits = GetDefaultCacheShardBits(capacity);
}
std::shared_ptr<Cache> cache = std::make_shared<LRUCache>(opts);
if (secondary_cache) {
cache = std::make_shared<CacheWithSecondaryAdapter>(cache, secondary_cache);
}
return cache;
}
std::shared_ptr<RowCache> LRUCacheOptions::MakeSharedRowCache() const {
if (secondary_cache) {
// Not allowed for a RowCache
return nullptr;
}
// Works while RowCache is an alias for Cache
return MakeSharedCache();
}
} // namespace ROCKSDB_NAMESPACE
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