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+// Copyright (c) 2018-Present Red Hat Inc.  All rights reserved.
+//
+// Copyright (c) 2011-2018, Facebook, Inc.  All rights reserved.
+// This source code is licensed under both the GPLv2 and Apache 2.0 License
+//
+// 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.
+
+#ifndef ROCKSDB_BINNED_LRU_CACHE
+#define ROCKSDB_BINNED_LRU_CACHE
+
+#include <string>
+#include <mutex>
+
+#include "ShardedCache.h"
+#include "common/autovector.h"
+#include "common/dout.h"
+#include "include/ceph_assert.h"
+#include "common/ceph_context.h"
+
+namespace rocksdb_cache {
+
+// LRU cache implementation
+
+// An entry is a variable length heap-allocated structure.
+// Entries are referenced by cache and/or by any external entity.
+// The cache keeps all its entries in table. Some elements
+// are also stored on LRU list.
+//
+// BinnedLRUHandle can be in these states:
+// 1. Referenced externally AND in hash table.
+//  In that case the entry is *not* in the LRU. (refs > 1 && in_cache == true)
+// 2. Not referenced externally and in hash table. In that case the entry is
+// in the LRU and can be freed. (refs == 1 && in_cache == true)
+// 3. Referenced externally and not in hash table. In that case the entry is
+// in not on LRU and not in table. (refs >= 1 && in_cache == false)
+//
+// All newly created BinnedLRUHandles are in state 1. If you call
+// BinnedLRUCacheShard::Release
+// on entry in state 1, it will go into state 2. To move from state 1 to
+// state 3, either call BinnedLRUCacheShard::Erase or BinnedLRUCacheShard::Insert with the
+// same key.
+// To move from state 2 to state 1, use BinnedLRUCacheShard::Lookup.
+// Before destruction, make sure that no handles are in state 1. This means
+// that any successful BinnedLRUCacheShard::Lookup/BinnedLRUCacheShard::Insert have a
+// matching
+// RUCache::Release (to move into state 2) or BinnedLRUCacheShard::Erase (for state 3)
+
+std::shared_ptr<rocksdb::Cache> NewBinnedLRUCache(
+    CephContext *c,
+    size_t capacity,
+    int num_shard_bits = -1,
+    bool strict_capacity_limit = false,
+    double high_pri_pool_ratio = 0.0);
+
+struct BinnedLRUHandle {
+  void* value;
+  void (*deleter)(const rocksdb::Slice&, void* value);
+  BinnedLRUHandle* next_hash;
+  BinnedLRUHandle* next;
+  BinnedLRUHandle* prev;
+  size_t charge;  // TODO(opt): Only allow uint32_t?
+  size_t key_length;
+  uint32_t refs;     // a number of refs to this entry
+                     // cache itself is counted as 1
+
+  // Include the following flags:
+  //   in_cache:    whether this entry is referenced by the hash table.
+  //   is_high_pri: whether this entry is high priority entry.
+  //   in_high_pri_pool: whether this entry is in high-pri pool.
+  char flags;
+
+  uint32_t hash;     // Hash of key(); used for fast sharding and comparisons
+
+  char* key_data = nullptr;  // Beginning of key
+
+  rocksdb::Slice key() const {
+    // For cheaper lookups, we allow a temporary Handle object
+    // to store a pointer to a key in "value".
+    if (next == this) {
+      return *(reinterpret_cast<rocksdb::Slice*>(value));
+    } else {
+      return rocksdb::Slice(key_data, key_length);
+    }
+  }
+
+  bool InCache() { return flags & 1; }
+  bool IsHighPri() { return flags & 2; }
+  bool InHighPriPool() { return flags & 4; }
+  bool HasHit() { return flags & 8; }
+
+  void SetInCache(bool in_cache) {
+    if (in_cache) {
+      flags |= 1;
+    } else {
+      flags &= ~1;
+    }
+  }
+
+  void SetPriority(rocksdb::Cache::Priority priority) {
+    if (priority == rocksdb::Cache::Priority::HIGH) {
+      flags |= 2;
+    } else {
+      flags &= ~2;
+    }
+  }
+
+  void SetInHighPriPool(bool in_high_pri_pool) {
+    if (in_high_pri_pool) {
+      flags |= 4;
+    } else {
+      flags &= ~4;
+    }
+  }
+
+  void SetHit() { flags |= 8; }
+
+  void Free() {
+    ceph_assert((refs == 1 && InCache()) || (refs == 0 && !InCache()));
+    if (deleter) {
+      (*deleter)(key(), value);
+    }
+    delete[] key_data;
+    delete this;
+  }
+};
+
+// 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 BinnedLRUHandleTable {
+ public:
+  BinnedLRUHandleTable();
+  ~BinnedLRUHandleTable();
+
+  BinnedLRUHandle* Lookup(const rocksdb::Slice& key, uint32_t hash);
+  BinnedLRUHandle* Insert(BinnedLRUHandle* h);
+  BinnedLRUHandle* Remove(const rocksdb::Slice& key, uint32_t hash);
+
+  template <typename T>
+  void ApplyToAllCacheEntries(T func) {
+    for (uint32_t i = 0; i < length_; i++) {
+      BinnedLRUHandle* h = list_[i];
+      while (h != nullptr) {
+        auto n = h->next_hash;
+        ceph_assert(h->InCache());
+        func(h);
+        h = n;
+      }
+    }
+  }
+
+ 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.
+  BinnedLRUHandle** FindPointer(const rocksdb::Slice& key, uint32_t hash);
+
+  void Resize();
+
+  // The table consists of an array of buckets where each bucket is
+  // a linked list of cache entries that hash into the bucket.
+  BinnedLRUHandle** list_;
+  uint32_t length_;
+  uint32_t elems_;
+};
+
+// A single shard of sharded cache.
+class alignas(CACHE_LINE_SIZE) BinnedLRUCacheShard : public CacheShard {
+ public:
+  BinnedLRUCacheShard(CephContext *c, size_t capacity, bool strict_capacity_limit,
+                double high_pri_pool_ratio);
+  virtual ~BinnedLRUCacheShard();
+
+  // Separate from constructor so caller can easily make an array of BinnedLRUCache
+  // if current usage is more than new capacity, the function will attempt to
+  // free the needed space
+  virtual void SetCapacity(size_t capacity) override;
+
+  // Set the flag to reject insertion if cache if full.
+  virtual void SetStrictCapacityLimit(bool strict_capacity_limit) override;
+
+  // Set percentage of capacity reserved for high-pri cache entries.
+  void SetHighPriPoolRatio(double high_pri_pool_ratio);
+
+  // Like Cache methods, but with an extra "hash" parameter.
+  virtual rocksdb::Status Insert(const rocksdb::Slice& key, uint32_t hash, void* value,
+                        size_t charge,
+                        void (*deleter)(const rocksdb::Slice& key, void* value),
+                        rocksdb::Cache::Handle** handle,
+                        rocksdb::Cache::Priority priority) override;
+  virtual rocksdb::Cache::Handle* Lookup(const rocksdb::Slice& key, uint32_t hash) override;
+  virtual bool Ref(rocksdb::Cache::Handle* handle) override;
+  virtual bool Release(rocksdb::Cache::Handle* handle,
+                       bool force_erase = false) override;
+  virtual void Erase(const rocksdb::Slice& key, uint32_t hash) override;
+
+  // Although in some platforms the update of size_t is atomic, to make sure
+  // GetUsage() and GetPinnedUsage() work correctly under any platform, we'll
+  // protect them with mutex_.
+
+  virtual size_t GetUsage() const override;
+  virtual size_t GetPinnedUsage() const override;
+
+  virtual void ApplyToAllCacheEntries(void (*callback)(void*, size_t),
+                                      bool thread_safe) override;
+
+  virtual void EraseUnRefEntries() override;
+
+  virtual std::string GetPrintableOptions() const override;
+
+  void TEST_GetLRUList(BinnedLRUHandle** lru, BinnedLRUHandle** lru_low_pri);
+
+  //  Retrieves number of elements in LRU, for unit test purpose only
+  //  not threadsafe
+  size_t TEST_GetLRUSize();
+
+  //  Retrieves high pri pool ratio
+  double GetHighPriPoolRatio() const;
+
+  // Retrieves high pri pool usage
+  size_t GetHighPriPoolUsage() const;
+
+ private:
+  CephContext *cct;
+  void LRU_Remove(BinnedLRUHandle* e);
+  void LRU_Insert(BinnedLRUHandle* e);
+
+  // Overflow the last entry in high-pri pool to low-pri pool until size of
+  // high-pri pool is no larger than the size specify by high_pri_pool_pct.
+  void MaintainPoolSize();
+
+  // Just reduce the reference count by 1.
+  // Return true if last reference
+  bool Unref(BinnedLRUHandle* 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, ceph::autovector<BinnedLRUHandle*>* deleted);
+
+  // Initialized before use.
+  size_t capacity_;
+
+  // Memory size for entries in high-pri pool.
+  size_t high_pri_pool_usage_;
+
+  // Whether to reject insertion if cache reaches its full capacity.
+  bool strict_capacity_limit_;
+
+  // Ratio of capacity reserved for high priority cache entries.
+  double high_pri_pool_ratio_;
+
+  // High-pri pool size, equals to capacity * high_pri_pool_ratio.
+  // Remember the value to avoid recomputing each time.
+  double high_pri_pool_capacity_;
+
+  // 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
+  BinnedLRUHandle lru_;
+
+  // Pointer to head of low-pri pool in LRU list.
+  BinnedLRUHandle* 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-----------
+  BinnedLRUHandleTable 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 std::mutex mutex_;
+};
+
+class BinnedLRUCache : public ShardedCache {
+ public:
+  BinnedLRUCache(CephContext *c, size_t capacity, int num_shard_bits,
+      bool strict_capacity_limit, double high_pri_pool_ratio);
+  virtual ~BinnedLRUCache();
+  virtual const char* Name() const override { return "BinnedLRUCache"; }
+  virtual CacheShard* GetShard(int shard) override;
+  virtual const CacheShard* GetShard(int shard) const override;
+  virtual void* Value(Handle* handle) override;
+  virtual size_t GetCharge(Handle* handle) const override;
+  virtual uint32_t GetHash(Handle* handle) const override;
+  virtual void DisownData() override;
+
+  //  Retrieves number of elements in LRU, for unit test purpose only
+  size_t TEST_GetLRUSize();
+  // Sets the high pri pool ratio
+  void SetHighPriPoolRatio(double high_pri_pool_ratio);
+  //  Retrieves high pri pool ratio
+  double GetHighPriPoolRatio() const;
+  // Retrieves high pri pool usage
+  size_t GetHighPriPoolUsage() const;
+
+  // PriorityCache
+  virtual int64_t request_cache_bytes(
+      PriorityCache::Priority pri, uint64_t total_cache) const;
+  virtual int64_t commit_cache_size(uint64_t total_cache);
+  virtual int64_t get_committed_size() const {
+    return GetCapacity();
+  }
+  virtual std::string get_cache_name() const {
+    return "RocksDB Binned LRU Cache";
+  }
+
+ private:
+  CephContext *cct;
+  BinnedLRUCacheShard* shards_;
+  int num_shards_ = 0;
+};
+
+}  // namespace rocksdb_cache
+
+#endif // ROCKSDB_BINNED_LRU_CACHE