Fork and simplify LRUCache for developing enhancements (#9917)
Summary: To support a project to prototype and evaluate algorithmic enhancments and alternatives to LRUCache, here I have separated out LRUCache into internal-only "FastLRUCache" and cut it down to essentials, so that details like secondary cache handling and priorities do not interfere with prototyping. These can be re-integrated later as needed, along with refactoring to minimize code duplication (which would slow down prototyping for now). Pull Request resolved: https://github.com/facebook/rocksdb/pull/9917 Test Plan: unit tests updated to ensure basic functionality has (likely) been preserved Reviewed By: anand1976 Differential Revision: D35995554 Pulled By: pdillinger fbshipit-source-id: d67b20b7ada3b5d3bfe56d897a73885894a1d9dbmain
Peter Dillinger
3 years ago
committed by
Facebook GitHub Bot
parent
4b9a1a2f56
commit
bb87164db3
@ -0,0 +1,511 @@ |
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "cache/fast_lru_cache.h" |
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#include <cassert> |
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#include <cstdint> |
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#include <cstdio> |
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#include "monitoring/perf_context_imp.h" |
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#include "monitoring/statistics.h" |
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#include "port/lang.h" |
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#include "util/mutexlock.h" |
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namespace ROCKSDB_NAMESPACE { |
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namespace fast_lru_cache { |
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LRUHandleTable::LRUHandleTable(int max_upper_hash_bits) |
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: length_bits_(/* historical starting size*/ 4), |
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list_(new LRUHandle* [size_t{1} << length_bits_] {}), |
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elems_(0), |
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max_length_bits_(max_upper_hash_bits) {} |
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LRUHandleTable::~LRUHandleTable() { |
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ApplyToEntriesRange( |
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[](LRUHandle* h) { |
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if (!h->HasRefs()) { |
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h->Free(); |
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} |
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}, |
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0, uint32_t{1} << length_bits_); |
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} |
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LRUHandle* LRUHandleTable::Lookup(const Slice& key, uint32_t hash) { |
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return *FindPointer(key, hash); |
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} |
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LRUHandle* LRUHandleTable::Insert(LRUHandle* h) { |
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LRUHandle** ptr = FindPointer(h->key(), h->hash); |
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LRUHandle* old = *ptr; |
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h->next_hash = (old == nullptr ? nullptr : old->next_hash); |
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*ptr = h; |
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if (old == nullptr) { |
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++elems_; |
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if ((elems_ >> length_bits_) > 0) { // elems_ >= length
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// Since each cache entry is fairly large, we aim for a small
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// average linked list length (<= 1).
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Resize(); |
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} |
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} |
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return old; |
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} |
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LRUHandle* LRUHandleTable::Remove(const Slice& key, uint32_t hash) { |
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LRUHandle** ptr = FindPointer(key, hash); |
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LRUHandle* result = *ptr; |
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if (result != nullptr) { |
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*ptr = result->next_hash; |
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--elems_; |
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} |
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return result; |
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} |
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LRUHandle** LRUHandleTable::FindPointer(const Slice& key, uint32_t hash) { |
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LRUHandle** ptr = &list_[hash >> (32 - length_bits_)]; |
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while (*ptr != nullptr && ((*ptr)->hash != hash || key != (*ptr)->key())) { |
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ptr = &(*ptr)->next_hash; |
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} |
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return ptr; |
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} |
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void LRUHandleTable::Resize() { |
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if (length_bits_ >= max_length_bits_) { |
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// Due to reaching limit of hash information, if we made the table bigger,
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// we would allocate more addresses but only the same number would be used.
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return; |
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} |
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if (length_bits_ >= 31) { |
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// Avoid undefined behavior shifting uint32_t by 32.
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return; |
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} |
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uint32_t old_length = uint32_t{1} << length_bits_; |
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int new_length_bits = length_bits_ + 1; |
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std::unique_ptr<LRUHandle* []> new_list { |
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new LRUHandle* [size_t{1} << new_length_bits] {} |
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}; |
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uint32_t count = 0; |
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for (uint32_t i = 0; i < old_length; i++) { |
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LRUHandle* h = list_[i]; |
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while (h != nullptr) { |
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LRUHandle* next = h->next_hash; |
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uint32_t hash = h->hash; |
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LRUHandle** ptr = &new_list[hash >> (32 - new_length_bits)]; |
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h->next_hash = *ptr; |
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*ptr = h; |
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h = next; |
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count++; |
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} |
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} |
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assert(elems_ == count); |
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list_ = std::move(new_list); |
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length_bits_ = new_length_bits; |
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} |
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LRUCacheShard::LRUCacheShard(size_t capacity, bool strict_capacity_limit, |
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CacheMetadataChargePolicy metadata_charge_policy, |
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int max_upper_hash_bits) |
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: capacity_(0), |
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strict_capacity_limit_(strict_capacity_limit), |
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table_(max_upper_hash_bits), |
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usage_(0), |
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lru_usage_(0) { |
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set_metadata_charge_policy(metadata_charge_policy); |
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// Make empty circular linked list.
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lru_.next = &lru_; |
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lru_.prev = &lru_; |
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lru_low_pri_ = &lru_; |
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SetCapacity(capacity); |
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} |
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void LRUCacheShard::EraseUnRefEntries() { |
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autovector<LRUHandle*> last_reference_list; |
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{ |
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MutexLock l(&mutex_); |
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while (lru_.next != &lru_) { |
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LRUHandle* old = lru_.next; |
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// LRU list contains only elements which can be evicted.
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assert(old->InCache() && !old->HasRefs()); |
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LRU_Remove(old); |
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table_.Remove(old->key(), old->hash); |
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old->SetInCache(false); |
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size_t total_charge = old->CalcTotalCharge(metadata_charge_policy_); |
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assert(usage_ >= total_charge); |
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usage_ -= total_charge; |
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last_reference_list.push_back(old); |
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} |
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} |
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// Free the entries here outside of mutex for performance reasons.
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for (auto entry : last_reference_list) { |
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entry->Free(); |
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} |
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} |
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void LRUCacheShard::ApplyToSomeEntries( |
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const std::function<void(const Slice& key, void* value, size_t charge, |
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DeleterFn deleter)>& callback, |
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uint32_t average_entries_per_lock, uint32_t* state) { |
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// The state is essentially going to be the starting hash, which works
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// nicely even if we resize between calls because we use upper-most
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// hash bits for table indexes.
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MutexLock l(&mutex_); |
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uint32_t length_bits = table_.GetLengthBits(); |
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uint32_t length = uint32_t{1} << length_bits; |
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assert(average_entries_per_lock > 0); |
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// Assuming we are called with same average_entries_per_lock repeatedly,
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// this simplifies some logic (index_end will not overflow).
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assert(average_entries_per_lock < length || *state == 0); |
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uint32_t index_begin = *state >> (32 - length_bits); |
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uint32_t index_end = index_begin + average_entries_per_lock; |
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if (index_end >= length) { |
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// Going to end
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index_end = length; |
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*state = UINT32_MAX; |
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} else { |
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*state = index_end << (32 - length_bits); |
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} |
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table_.ApplyToEntriesRange( |
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[callback](LRUHandle* h) { |
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callback(h->key(), h->value, h->charge, h->deleter); |
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}, |
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index_begin, index_end); |
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} |
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void LRUCacheShard::LRU_Remove(LRUHandle* e) { |
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assert(e->next != nullptr); |
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assert(e->prev != nullptr); |
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e->next->prev = e->prev; |
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e->prev->next = e->next; |
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e->prev = e->next = nullptr; |
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size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_); |
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assert(lru_usage_ >= total_charge); |
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lru_usage_ -= total_charge; |
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} |
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void LRUCacheShard::LRU_Insert(LRUHandle* e) { |
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assert(e->next == nullptr); |
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assert(e->prev == nullptr); |
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size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_); |
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// Inset "e" to head of LRU list.
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e->next = &lru_; |
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e->prev = lru_.prev; |
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e->prev->next = e; |
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e->next->prev = e; |
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lru_usage_ += total_charge; |
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} |
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void LRUCacheShard::EvictFromLRU(size_t charge, |
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autovector<LRUHandle*>* deleted) { |
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while ((usage_ + charge) > capacity_ && lru_.next != &lru_) { |
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LRUHandle* old = lru_.next; |
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// LRU list contains only elements which can be evicted.
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assert(old->InCache() && !old->HasRefs()); |
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LRU_Remove(old); |
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table_.Remove(old->key(), old->hash); |
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old->SetInCache(false); |
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size_t old_total_charge = old->CalcTotalCharge(metadata_charge_policy_); |
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assert(usage_ >= old_total_charge); |
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usage_ -= old_total_charge; |
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deleted->push_back(old); |
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} |
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} |
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void LRUCacheShard::SetCapacity(size_t capacity) { |
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autovector<LRUHandle*> last_reference_list; |
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{ |
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MutexLock l(&mutex_); |
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capacity_ = capacity; |
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EvictFromLRU(0, &last_reference_list); |
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} |
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// Free the entries here outside of mutex for performance reasons.
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for (auto entry : last_reference_list) { |
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entry->Free(); |
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} |
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} |
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void LRUCacheShard::SetStrictCapacityLimit(bool strict_capacity_limit) { |
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MutexLock l(&mutex_); |
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strict_capacity_limit_ = strict_capacity_limit; |
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} |
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Status LRUCacheShard::InsertItem(LRUHandle* e, Cache::Handle** handle, |
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bool free_handle_on_fail) { |
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Status s = Status::OK(); |
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autovector<LRUHandle*> last_reference_list; |
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size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_); |
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{ |
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MutexLock l(&mutex_); |
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// Free the space following strict LRU policy until enough space
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// is freed or the lru list is empty.
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EvictFromLRU(total_charge, &last_reference_list); |
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if ((usage_ + total_charge) > capacity_ && |
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(strict_capacity_limit_ || handle == nullptr)) { |
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e->SetInCache(false); |
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if (handle == nullptr) { |
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// Don't insert the entry but still return ok, as if the entry inserted
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// into cache and get evicted immediately.
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last_reference_list.push_back(e); |
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} else { |
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if (free_handle_on_fail) { |
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delete[] reinterpret_cast<char*>(e); |
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*handle = nullptr; |
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} |
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s = Status::Incomplete("Insert failed due to LRU cache being full."); |
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} |
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} else { |
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// Insert into the cache. Note that the cache might get larger than its
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// capacity if not enough space was freed up.
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LRUHandle* old = table_.Insert(e); |
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usage_ += total_charge; |
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if (old != nullptr) { |
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s = Status::OkOverwritten(); |
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assert(old->InCache()); |
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old->SetInCache(false); |
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if (!old->HasRefs()) { |
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// old is on LRU because it's in cache and its reference count is 0.
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LRU_Remove(old); |
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size_t old_total_charge = |
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old->CalcTotalCharge(metadata_charge_policy_); |
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assert(usage_ >= old_total_charge); |
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usage_ -= old_total_charge; |
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last_reference_list.push_back(old); |
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} |
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} |
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if (handle == nullptr) { |
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LRU_Insert(e); |
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} else { |
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// If caller already holds a ref, no need to take one here.
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if (!e->HasRefs()) { |
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e->Ref(); |
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} |
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*handle = reinterpret_cast<Cache::Handle*>(e); |
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} |
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} |
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} |
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// Free the entries here outside of mutex for performance reasons.
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for (auto entry : last_reference_list) { |
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entry->Free(); |
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} |
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return s; |
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} |
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Cache::Handle* LRUCacheShard::Lookup(const Slice& key, uint32_t hash) { |
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LRUHandle* e = nullptr; |
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{ |
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MutexLock l(&mutex_); |
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e = table_.Lookup(key, hash); |
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if (e != nullptr) { |
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assert(e->InCache()); |
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if (!e->HasRefs()) { |
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// The entry is in LRU since it's in hash and has no external references
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LRU_Remove(e); |
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} |
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e->Ref(); |
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} |
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} |
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return reinterpret_cast<Cache::Handle*>(e); |
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} |
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bool LRUCacheShard::Ref(Cache::Handle* h) { |
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LRUHandle* e = reinterpret_cast<LRUHandle*>(h); |
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MutexLock l(&mutex_); |
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// To create another reference - entry must be already externally referenced.
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assert(e->HasRefs()); |
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e->Ref(); |
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return true; |
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} |
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bool LRUCacheShard::Release(Cache::Handle* handle, bool erase_if_last_ref) { |
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if (handle == nullptr) { |
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return false; |
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} |
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LRUHandle* e = reinterpret_cast<LRUHandle*>(handle); |
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bool last_reference = false; |
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{ |
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MutexLock l(&mutex_); |
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last_reference = e->Unref(); |
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if (last_reference && e->InCache()) { |
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// The item is still in cache, and nobody else holds a reference to it.
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if (usage_ > capacity_ || erase_if_last_ref) { |
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// The LRU list must be empty since the cache is full.
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assert(lru_.next == &lru_ || erase_if_last_ref); |
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// Take this opportunity and remove the item.
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table_.Remove(e->key(), e->hash); |
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e->SetInCache(false); |
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} else { |
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// Put the item back on the LRU list, and don't free it.
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LRU_Insert(e); |
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last_reference = false; |
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} |
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} |
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// If it was the last reference, then decrement the cache usage.
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if (last_reference) { |
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size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_); |
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assert(usage_ >= total_charge); |
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usage_ -= total_charge; |
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} |
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} |
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// Free the entry here outside of mutex for performance reasons.
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if (last_reference) { |
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e->Free(); |
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} |
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return last_reference; |
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} |
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Status LRUCacheShard::Insert(const Slice& key, uint32_t hash, void* value, |
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size_t charge, Cache::DeleterFn deleter, |
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Cache::Handle** handle, |
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Cache::Priority /*priority*/) { |
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// Allocate the memory here outside of the mutex.
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// If the cache is full, we'll have to release it.
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// It shouldn't happen very often though.
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LRUHandle* e = reinterpret_cast<LRUHandle*>( |
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new char[sizeof(LRUHandle) - 1 + key.size()]); |
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e->value = value; |
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e->flags = 0; |
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e->deleter = deleter; |
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e->charge = charge; |
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e->key_length = key.size(); |
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e->hash = hash; |
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e->refs = 0; |
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e->next = e->prev = nullptr; |
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e->SetInCache(true); |
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memcpy(e->key_data, key.data(), key.size()); |
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return InsertItem(e, handle, /* free_handle_on_fail */ true); |
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} |
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void LRUCacheShard::Erase(const Slice& key, uint32_t hash) { |
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LRUHandle* e; |
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bool last_reference = false; |
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{ |
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MutexLock l(&mutex_); |
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e = table_.Remove(key, hash); |
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if (e != nullptr) { |
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assert(e->InCache()); |
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e->SetInCache(false); |
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if (!e->HasRefs()) { |
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// The entry is in LRU since it's in hash and has no external references
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LRU_Remove(e); |
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size_t total_charge = e->CalcTotalCharge(metadata_charge_policy_); |
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assert(usage_ >= total_charge); |
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usage_ -= total_charge; |
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last_reference = true; |
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} |
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} |
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} |
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// Free the entry here outside of mutex for performance reasons.
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// last_reference will only be true if e != nullptr.
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if (last_reference) { |
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e->Free(); |
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} |
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} |
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size_t LRUCacheShard::GetUsage() const { |
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MutexLock l(&mutex_); |
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return usage_; |
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} |
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size_t LRUCacheShard::GetPinnedUsage() const { |
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MutexLock l(&mutex_); |
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assert(usage_ >= lru_usage_); |
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return usage_ - lru_usage_; |
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} |
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std::string LRUCacheShard::GetPrintableOptions() const { return std::string{}; } |
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LRUCache::LRUCache(size_t capacity, int num_shard_bits, |
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bool strict_capacity_limit, |
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CacheMetadataChargePolicy metadata_charge_policy) |
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: ShardedCache(capacity, num_shard_bits, strict_capacity_limit) { |
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num_shards_ = 1 << num_shard_bits; |
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shards_ = reinterpret_cast<LRUCacheShard*>( |
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port::cacheline_aligned_alloc(sizeof(LRUCacheShard) * num_shards_)); |
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size_t per_shard = (capacity + (num_shards_ - 1)) / num_shards_; |
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for (int i = 0; i < num_shards_; i++) { |
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new (&shards_[i]) |
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LRUCacheShard(per_shard, strict_capacity_limit, metadata_charge_policy, |
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/* max_upper_hash_bits */ 32 - num_shard_bits); |
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} |
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} |
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LRUCache::~LRUCache() { |
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if (shards_ != nullptr) { |
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assert(num_shards_ > 0); |
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for (int i = 0; i < num_shards_; i++) { |
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shards_[i].~LRUCacheShard(); |
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} |
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port::cacheline_aligned_free(shards_); |
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} |
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} |
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CacheShard* LRUCache::GetShard(uint32_t shard) { |
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return reinterpret_cast<CacheShard*>(&shards_[shard]); |
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} |
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const CacheShard* LRUCache::GetShard(uint32_t shard) const { |
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return reinterpret_cast<CacheShard*>(&shards_[shard]); |
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} |
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void* LRUCache::Value(Handle* handle) { |
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return reinterpret_cast<const LRUHandle*>(handle)->value; |
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} |
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size_t LRUCache::GetCharge(Handle* handle) const { |
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return reinterpret_cast<const LRUHandle*>(handle)->charge; |
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} |
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Cache::DeleterFn LRUCache::GetDeleter(Handle* handle) const { |
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auto h = reinterpret_cast<const LRUHandle*>(handle); |
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return h->deleter; |
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} |
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uint32_t LRUCache::GetHash(Handle* handle) const { |
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return reinterpret_cast<const LRUHandle*>(handle)->hash; |
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} |
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void LRUCache::DisownData() { |
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// Leak data only if that won't generate an ASAN/valgrind warning.
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if (!kMustFreeHeapAllocations) { |
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shards_ = nullptr; |
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num_shards_ = 0; |
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} |
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} |
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} // namespace fast_lru_cache
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std::shared_ptr<Cache> NewFastLRUCache( |
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size_t capacity, int num_shard_bits, bool strict_capacity_limit, |
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CacheMetadataChargePolicy metadata_charge_policy) { |
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if (num_shard_bits >= 20) { |
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return nullptr; // The cache cannot be sharded into too many fine pieces.
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} |
||||
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
|
||||
@ -0,0 +1,299 @@ |
||||
// 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.
|
||||
#pragma once |
||||
|
||||
#include <memory> |
||||
#include <string> |
||||
|
||||
#include "cache/sharded_cache.h" |
||||
#include "port/lang.h" |
||||
#include "port/malloc.h" |
||||
#include "port/port.h" |
||||
#include "rocksdb/secondary_cache.h" |
||||
#include "util/autovector.h" |
||||
|
||||
namespace ROCKSDB_NAMESPACE { |
||||
namespace fast_lru_cache { |
||||
|
||||
// An experimental (under development!) alternative to LRUCache
|
||||
|
||||
struct LRUHandle { |
||||
void* value; |
||||
Cache::DeleterFn deleter; |
||||
LRUHandle* next_hash; |
||||
LRUHandle* next; |
||||
LRUHandle* prev; |
||||
size_t charge; // TODO(opt): Only allow uint32_t?
|
||||
size_t key_length; |
||||
// The hash of key(). Used for fast sharding and comparisons.
|
||||
uint32_t hash; |
||||
// The number of external refs to this entry. The cache itself is not counted.
|
||||
uint32_t refs; |
||||
|
||||
enum Flags : uint8_t { |
||||
// Whether this entry is referenced by the hash table.
|
||||
IN_CACHE = (1 << 0), |
||||
}; |
||||
uint8_t flags; |
||||
|
||||
// Beginning of the key (MUST BE THE LAST FIELD IN THIS STRUCT!)
|
||||
char key_data[1]; |
||||
|
||||
Slice key() const { return Slice(key_data, key_length); } |
||||
|
||||
// Increase the reference count by 1.
|
||||
void Ref() { refs++; } |
||||
|
||||
// Just reduce the reference count by 1. Return true if it was last reference.
|
||||
bool Unref() { |
||||
assert(refs > 0); |
||||
refs--; |
||||
return refs == 0; |
||||
} |
||||
|
||||
// Return true if there are external refs, false otherwise.
|
||||
bool HasRefs() const { return refs > 0; } |
||||
|
||||
bool InCache() const { return flags & IN_CACHE; } |
||||
|
||||
void SetInCache(bool in_cache) { |
||||
if (in_cache) { |
||||
flags |= IN_CACHE; |
||||
} else { |
||||
flags &= ~IN_CACHE; |
||||
} |
||||
} |
||||
|
||||
void Free() { |
||||
assert(refs == 0); |
||||
if (deleter) { |
||||
(*deleter)(key(), value); |
||||
} |
||||
delete[] reinterpret_cast<char*>(this); |
||||
} |
||||
|
||||
// Calculate the memory usage by metadata.
|
||||
inline size_t CalcTotalCharge( |
||||
CacheMetadataChargePolicy metadata_charge_policy) { |
||||
size_t meta_charge = 0; |
||||
if (metadata_charge_policy == kFullChargeCacheMetadata) { |
||||
#ifdef ROCKSDB_MALLOC_USABLE_SIZE |
||||
meta_charge += malloc_usable_size(static_cast<void*>(this)); |
||||
#else |
||||
// This is the size that is used when a new handle is created.
|
||||
meta_charge += sizeof(LRUHandle) - 1 + key_length; |
||||
#endif |
||||
} |
||||
return charge + meta_charge; |
||||
} |
||||
}; |
||||
|
||||
// We provide our own simple hash table since it removes a whole bunch
|
||||
// of porting hacks and is also faster than some of the built-in hash
|
||||
// table implementations in some of the compiler/runtime combinations
|
||||
// we have tested. E.g., readrandom speeds up by ~5% over the g++
|
||||
// 4.4.3's builtin hashtable.
|
||||
class LRUHandleTable { |
||||
public: |
||||
// If the table uses more hash bits than `max_upper_hash_bits`,
|
||||
// it will eat into the bits used for sharding, which are constant
|
||||
// for a given LRUHandleTable.
|
||||
explicit LRUHandleTable(int max_upper_hash_bits); |
||||
~LRUHandleTable(); |
||||
|
||||
LRUHandle* Lookup(const Slice& key, uint32_t hash); |
||||
LRUHandle* Insert(LRUHandle* h); |
||||
LRUHandle* Remove(const Slice& key, uint32_t hash); |
||||
|
||||
template <typename T> |
||||
void ApplyToEntriesRange(T func, uint32_t index_begin, uint32_t index_end) { |
||||
for (uint32_t i = index_begin; i < index_end; i++) { |
||||
LRUHandle* h = list_[i]; |
||||
while (h != nullptr) { |
||||
auto n = h->next_hash; |
||||
assert(h->InCache()); |
||||
func(h); |
||||
h = n; |
||||
} |
||||
} |
||||
} |
||||
|
||||
int GetLengthBits() const { return length_bits_; } |
||||
|
||||
private: |
||||
// Return a pointer to slot that points to a cache entry that
|
||||
// matches key/hash. If there is no such cache entry, return a
|
||||
// pointer to the trailing slot in the corresponding linked list.
|
||||
LRUHandle** FindPointer(const Slice& key, uint32_t hash); |
||||
|
||||
void Resize(); |
||||
|
||||
// Number of hash bits (upper because lower bits used for sharding)
|
||||
// used for table index. Length == 1 << length_bits_
|
||||
int length_bits_; |
||||
|
||||
// The table consists of an array of buckets where each bucket is
|
||||
// a linked list of cache entries that hash into the bucket.
|
||||
std::unique_ptr<LRUHandle*[]> list_; |
||||
|
||||
// Number of elements currently in the table.
|
||||
uint32_t elems_; |
||||
|
||||
// Set from max_upper_hash_bits (see constructor).
|
||||
const int max_length_bits_; |
||||
}; |
||||
|
||||
// A single shard of sharded cache.
|
||||
class ALIGN_AS(CACHE_LINE_SIZE) LRUCacheShard final : public CacheShard { |
||||
public: |
||||
LRUCacheShard(size_t capacity, bool strict_capacity_limit, |
||||
CacheMetadataChargePolicy metadata_charge_policy, |
||||
int max_upper_hash_bits); |
||||
~LRUCacheShard() override = default; |
||||
|
||||
// Separate from constructor so caller can easily make an array of LRUCache
|
||||
// if current usage is more than new capacity, the function will attempt to
|
||||
// free the needed space.
|
||||
void SetCapacity(size_t capacity) override; |
||||
|
||||
// Set the flag to reject insertion if cache if full.
|
||||
void SetStrictCapacityLimit(bool strict_capacity_limit) override; |
||||
|
||||
// Like Cache methods, but with an extra "hash" parameter.
|
||||
Status Insert(const Slice& key, uint32_t hash, void* value, size_t charge, |
||||
Cache::DeleterFn deleter, Cache::Handle** handle, |
||||
Cache::Priority priority) override; |
||||
|
||||
Status Insert(const Slice& key, uint32_t hash, void* value, |
||||
const Cache::CacheItemHelper* helper, size_t charge, |
||||
Cache::Handle** handle, Cache::Priority priority) override { |
||||
return Insert(key, hash, value, charge, helper->del_cb, handle, priority); |
||||
} |
||||
|
||||
Cache::Handle* Lookup(const Slice& key, uint32_t hash, |
||||
const Cache::CacheItemHelper* /*helper*/, |
||||
const Cache::CreateCallback& /*create_cb*/, |
||||
Cache::Priority /*priority*/, bool /*wait*/, |
||||
Statistics* /*stats*/) override { |
||||
return Lookup(key, hash); |
||||
} |
||||
Cache::Handle* Lookup(const Slice& key, uint32_t hash) override; |
||||
|
||||
bool Release(Cache::Handle* handle, bool /*useful*/, |
||||
bool erase_if_last_ref) override { |
||||
return Release(handle, erase_if_last_ref); |
||||
} |
||||
bool IsReady(Cache::Handle* /*handle*/) override { return true; } |
||||
void Wait(Cache::Handle* /*handle*/) override {} |
||||
|
||||
bool Ref(Cache::Handle* handle) override; |
||||
bool Release(Cache::Handle* handle, bool erase_if_last_ref = false) override; |
||||
void Erase(const Slice& key, uint32_t hash) override; |
||||
|
||||
size_t GetUsage() const override; |
||||
size_t GetPinnedUsage() const override; |
||||
|
||||
void 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) override; |
||||
|
||||
void EraseUnRefEntries() override; |
||||
|
||||
std::string GetPrintableOptions() const override; |
||||
|
||||
private: |
||||
friend class LRUCache; |
||||
// Insert an item into the hash table and, if handle is null, insert into
|
||||
// the LRU list. Older items are evicted as necessary. If the cache is full
|
||||
// and free_handle_on_fail is true, the item is deleted and handle is set to
|
||||
// nullptr.
|
||||
Status InsertItem(LRUHandle* item, Cache::Handle** handle, |
||||
bool free_handle_on_fail); |
||||
|
||||
void LRU_Remove(LRUHandle* e); |
||||
void LRU_Insert(LRUHandle* e); |
||||
|
||||
// Free some space following strict LRU policy until enough space
|
||||
// to hold (usage_ + charge) is freed or the lru list is empty
|
||||
// This function is not thread safe - it needs to be executed while
|
||||
// holding the mutex_.
|
||||
void EvictFromLRU(size_t charge, autovector<LRUHandle*>* deleted); |
||||
|
||||
// Initialized before use.
|
||||
size_t capacity_; |
||||
|
||||
// Whether to reject insertion if cache reaches its full capacity.
|
||||
bool strict_capacity_limit_; |
||||
|
||||
// Dummy head of LRU list.
|
||||
// lru.prev is newest entry, lru.next is oldest entry.
|
||||
// LRU contains items which can be evicted, ie reference only by cache
|
||||
LRUHandle lru_; |
||||
|
||||
// Pointer to head of low-pri pool in LRU list.
|
||||
LRUHandle* lru_low_pri_; |
||||
|
||||
// ------------^^^^^^^^^^^^^-----------
|
||||
// Not frequently modified data members
|
||||
// ------------------------------------
|
||||
//
|
||||
// We separate data members that are updated frequently from the ones that
|
||||
// are not frequently updated so that they don't share the same cache line
|
||||
// which will lead into false cache sharing
|
||||
//
|
||||
// ------------------------------------
|
||||
// Frequently modified data members
|
||||
// ------------vvvvvvvvvvvvv-----------
|
||||
LRUHandleTable table_; |
||||
|
||||
// Memory size for entries residing in the cache.
|
||||
size_t usage_; |
||||
|
||||
// Memory size for entries residing only in the LRU list.
|
||||
size_t lru_usage_; |
||||
|
||||
// mutex_ protects the following state.
|
||||
// We don't count mutex_ as the cache's internal state so semantically we
|
||||
// don't mind mutex_ invoking the non-const actions.
|
||||
mutable port::Mutex mutex_; |
||||
}; |
||||
|
||||
class LRUCache |
||||
#ifdef NDEBUG |
||||
final |
||||
#endif |
||||
: public ShardedCache { |
||||
public: |
||||
LRUCache(size_t capacity, int num_shard_bits, bool strict_capacity_limit, |
||||
CacheMetadataChargePolicy metadata_charge_policy = |
||||
kDontChargeCacheMetadata); |
||||
~LRUCache() override; |
||||
const char* Name() const override { return "LRUCache"; } |
||||
CacheShard* GetShard(uint32_t shard) override; |
||||
const CacheShard* GetShard(uint32_t shard) const override; |
||||
void* Value(Handle* handle) override; |
||||
size_t GetCharge(Handle* handle) const override; |
||||
uint32_t GetHash(Handle* handle) const override; |
||||
DeleterFn GetDeleter(Handle* handle) const override; |
||||
void DisownData() override; |
||||
|
||||
private: |
||||
LRUCacheShard* shards_ = nullptr; |
||||
int num_shards_ = 0; |
||||
}; |
||||
} // namespace fast_lru_cache
|
||||
|
||||
std::shared_ptr<Cache> NewFastLRUCache( |
||||
size_t capacity, int num_shard_bits = -1, |
||||
bool strict_capacity_limit = false, |
||||
CacheMetadataChargePolicy metadata_charge_policy = |
||||
kDefaultCacheMetadataChargePolicy); |
||||
|
||||
} // namespace ROCKSDB_NAMESPACE
|
||||
Loading…
Reference in new issue