src/iocore/cache/RamCacheLRU.cc

/** @file

  A brief file description

  @section license License

  Licensed to the Apache Software Foundation (ASF) under one
  or more contributor license agreements.  See the NOTICE file
  distributed with this work for additional information
  regarding copyright ownership.  The ASF licenses this file
  to you under the Apache License, Version 2.0 (the
  "License"); you may not use this file except in compliance
  with the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
 */

#include "P_RamCache.h"
#include "P_CacheInternal.h"
#include "StripeSM.h"
#include "iocore/eventsystem/IOBuffer.h"
#include "tscore/CryptoHash.h"
#include "tscore/List.h"
#include <vector>
#include <iterator>

struct RamCacheLRUEntry {
  CryptoHash key;
  uint64_t   auxkey;
  LINK(RamCacheLRUEntry, lru_link);
  LINK(RamCacheLRUEntry, hash_link);
  Ptr<IOBufferData> data;
};

#define ENTRY_OVERHEAD 128 // per-entry overhead to consider when computing sizes

struct RamCacheLRU : public RamCache {
  int64_t max_bytes = 0;
  int64_t bytes     = 0;
  int64_t objects   = 0;

  // returns 1 on found/stored, 0 on not found/stored, if provided auxkey must match
  int     get(CryptoHash *key, Ptr<IOBufferData> *ret_data, uint64_t auxkey = 0) override;
  int     put(CryptoHash *key, IOBufferData *data, uint32_t len, bool copy = false, uint64_t auxkey = 0) override;
  int     fixup(const CryptoHash *key, uint64_t old_auxkey, uint64_t new_auxkey) override;
  int64_t size() const override;

  void init(int64_t max_bytes, StripeSM *stripe) override;

  // private
  std::vector<bool> seen;
  Que(RamCacheLRUEntry, lru_link) lru;
  DList(RamCacheLRUEntry, hash_link) *bucket = nullptr;
  int       nbuckets                         = 0;
  int       ibuckets                         = 0;
  StripeSM *stripe                           = nullptr;

  void              resize_hashtable();
  RamCacheLRUEntry *remove(RamCacheLRUEntry *e);
};

#ifdef DEBUG

namespace
{

DbgCtl dbg_ctl_ram_cache{"ram_cache"};

} // end anonymous namespace

#endif

int64_t
RamCacheLRU::size() const
{
  int64_t s = 0;
  forl_LL(RamCacheLRUEntry, e, lru)
  {
    s += sizeof(*e);
    s += sizeof(*e->data);
    s += e->data->block_size();
  }
  return s;
}

ClassAllocator<RamCacheLRUEntry, false> ramCacheLRUEntryAllocator("RamCacheLRUEntry");

static const int bucket_sizes[] = {8191,    16381,   32749,    65521,    131071,   262139,    524287,    1048573,   2097143,
                                   4194301, 8388593, 16777213, 33554393, 67108859, 134217689, 268435399, 536870909, 1073741827};

void
RamCacheLRU::resize_hashtable()
{
  ink_release_assert(ibuckets < static_cast<int>(std::size(bucket_sizes)));

  int anbuckets = bucket_sizes[ibuckets];
  DDbg(dbg_ctl_ram_cache, "resize hashtable %d", anbuckets);
  int64_t s                                      = anbuckets * sizeof(DList(RamCacheLRUEntry, hash_link));
  DList(RamCacheLRUEntry, hash_link) *new_bucket = static_cast<DList(RamCacheLRUEntry, hash_link) *>(ats_malloc(s));
  memset(static_cast<void *>(new_bucket), 0, s);
  if (bucket) {
    for (int64_t i = 0; i < nbuckets; i++) {
      RamCacheLRUEntry *e = nullptr;
      while ((e = bucket[i].pop())) {
        new_bucket[e->key.slice32(3) % anbuckets].push(e);
      }
    }
    ats_free(bucket);
  }
  bucket   = new_bucket;
  nbuckets = anbuckets;
  if (cache_config_ram_cache_use_seen_filter) {
    int size = bucket_sizes[ibuckets];

    seen.resize(size * 2); // Twice the size, to reduce collision risks.
    seen.assign(size * 2, false);
  }
}

void
RamCacheLRU::init(int64_t abytes, StripeSM *astripe)
{
  stripe    = astripe;
  max_bytes = abytes;
  DDbg(dbg_ctl_ram_cache, "initializing ram_cache %" PRId64 " bytes", abytes);
  if (!max_bytes) {
    return;
  }
  resize_hashtable();
}

int
RamCacheLRU::get(CryptoHash *key, Ptr<IOBufferData> *ret_data, uint64_t auxkey)
{
  if (!max_bytes) {
    return 0;
  }
  uint32_t          i = key->slice32(3) % nbuckets;
  RamCacheLRUEntry *e = bucket[i].head;
  while (e) {
    if (e->key == *key && e->auxkey == auxkey) {
      lru.remove(e);
      lru.enqueue(e);
      (*ret_data) = e->data;
      DDbg(dbg_ctl_ram_cache, "get %X %" PRIu64 " HIT", key->slice32(3), auxkey);
      ts::Metrics::Counter::increment(cache_rsb.ram_cache_hits);
      ts::Metrics::Counter::increment(stripe->cache_vol->vol_rsb.ram_cache_hits);

      return 1;
    }
    e = e->hash_link.next;
  }
  DDbg(dbg_ctl_ram_cache, "get %X %" PRIu64 " MISS", key->slice32(3), auxkey);
  ts::Metrics::Counter::increment(cache_rsb.ram_cache_misses);
  ts::Metrics::Counter::increment(stripe->cache_vol->vol_rsb.ram_cache_misses);

  return 0;
}

RamCacheLRUEntry *
RamCacheLRU::remove(RamCacheLRUEntry *e)
{
  RamCacheLRUEntry *ret = e->hash_link.next;
  uint32_t          b   = e->key.slice32(3) % nbuckets;
  bucket[b].remove(e);
  lru.remove(e);
  bytes -= ENTRY_OVERHEAD + e->data->block_size();
  ts::Metrics::Gauge::decrement(cache_rsb.ram_cache_bytes, ENTRY_OVERHEAD + e->data->block_size());
  ts::Metrics::Gauge::decrement(stripe->cache_vol->vol_rsb.ram_cache_bytes, ENTRY_OVERHEAD + e->data->block_size());

  DDbg(dbg_ctl_ram_cache, "put %X %" PRIu64 " FREED", e->key.slice32(3), e->auxkey);
  e->data = nullptr;
  THREAD_FREE(e, ramCacheLRUEntryAllocator, this_thread());
  objects--;
  return ret;
}

// ignore 'copy' since we don't touch the data
int
RamCacheLRU::put(CryptoHash *key, IOBufferData *data, [[maybe_unused]] uint32_t len, bool, uint64_t auxkey)
{
  if (!max_bytes) {
    return 0;
  }
  uint32_t i = key->slice32(3) % nbuckets;
  if ((cache_config_ram_cache_use_seen_filter == 1) ||
      // If proxy.config.cache.ram_cache.use_seen_filter is > 1,  and the cache is more than <n>% full, then use the seen filter.
      // <n>% is calculated based on this setting, with 2 == 50%, 3 == 67%, 4 == 75%, up to 9 == 90%.
      ((cache_config_ram_cache_use_seen_filter > 1) && (bytes >= max_bytes * (1 - (1 / cache_config_ram_cache_use_seen_filter))))) {
    uint32_t j = key->slice32(3) % (nbuckets * 2); // The seen filter bucket size is 2x

    if (!seen[j]) {
      DDbg(dbg_ctl_ram_cache, "put %X %" PRIu64 " len %d UNSEEN", key->slice32(3), auxkey, len);
      seen[j] = true;
      return 0;
    } else {
      seen[j] = false; // Clear the seen filter slot for future entries.
    }
  }

  RamCacheLRUEntry *e = bucket[i].head;
  while (e) {
    if (e->key == *key) {
      if (e->auxkey == auxkey) {
        lru.remove(e);
        lru.enqueue(e);
        return 1;
      } else { // discard when aux keys conflict
        e = remove(e);
        continue;
      }
    }
    e = e->hash_link.next;
  }
  e         = THREAD_ALLOC(ramCacheLRUEntryAllocator, this_ethread());
  e->key    = *key;
  e->auxkey = auxkey;
  e->data   = data;
  bucket[i].push(e);
  lru.enqueue(e);
  bytes += ENTRY_OVERHEAD + data->block_size();
  objects++;
  ts::Metrics::Gauge::increment(cache_rsb.ram_cache_bytes, ENTRY_OVERHEAD + data->block_size());
  ts::Metrics::Gauge::increment(stripe->cache_vol->vol_rsb.ram_cache_bytes, ENTRY_OVERHEAD + data->block_size());
  while (bytes > max_bytes) {
    RamCacheLRUEntry *ee = lru.dequeue();
    if (ee) {
      remove(ee);
    } else {
      break;
    }
  }
  DDbg(dbg_ctl_ram_cache, "put %X %" PRIu64 " INSERTED", key->slice32(3), auxkey);
  if (objects > nbuckets * 0.75) { // Resize when 75% "full"
    ++ibuckets;
    resize_hashtable();
  }
  return 1;
}

int
RamCacheLRU::fixup(const CryptoHash *key, uint64_t old_auxkey, uint64_t new_auxkey)
{
  if (!max_bytes) {
    return 0;
  }
  uint32_t          i = key->slice32(3) % nbuckets;
  RamCacheLRUEntry *e = bucket[i].head;
  while (e) {
    if (e->key == *key && e->auxkey == old_auxkey) {
      e->auxkey = new_auxkey;
      return 1;
    }
    e = e->hash_link.next;
  }
  return 0;
}

RamCache *
new_RamCacheLRU()
{
  return new RamCacheLRU;
}