no online eviction option patch

--------------------------------
this is to be used in conjunction with the
background evictors to completely disable
any hot path evictions - forcing all evictions
to occur via background threads

Author: byrnedj

cachelib/allocator/CacheAllocator.h

@@ -2996,7 +2996,7 @@ CacheAllocator<CacheTrait>::allocateInternalTier(TierId tid,
   }
 
   if (memory == nullptr) {
-    if (!evict) {
+    if (!evict || config_.noOnlineEviction) {
       return {};
     }
     memory = findEviction(tid, pid, cid);
@@ -3047,7 +3047,7 @@ CacheAllocator<CacheTrait>::allocateInternal(PoolId pid,
                                              uint32_t expiryTime) {
   auto tid = 0; /* TODO: consult admission policy */
   for(TierId tid = 0; tid < getNumTiers(); ++tid) {
-    bool evict = !config_.insertToFirstFreeTier || tid == getNumTiers() - 1;
+    bool evict = (!config_.insertToFirstFreeTier || tid == getNumTiers() - 1);
     auto handle = allocateInternalTier(tid, pid, key, size, creationTime,
                                        expiryTime, evict);
     if (handle) return handle;
@@ -4477,7 +4477,7 @@ CacheAllocator<CacheTrait>::getNextCandidate(TierId tid,
   bool isExpired = false;
   bool chainedItem = false;
   auto& mmContainer = getMMContainer(tid, pid, cid);
-  bool lastTier = tid+1 >= getNumTiers();
+  bool lastTier = tid+1 >= getNumTiers() || config_.noOnlineEviction;
 
   mmContainer.withEvictionIterator([this, tid, pid, cid, &candidate,
                                     &toRecycle, &toRecycleParent,

cachelib/allocator/CacheAllocatorConfig.h

@@ -315,6 +315,8 @@ class CacheAllocatorConfig {
 
   // Insert items to first free memory tier
   CacheAllocatorConfig& enableInsertToFirstFreeTier();
+  
+  CacheAllocatorConfig& enableNoOnlineEviction();
 
   // Passes in a callback to initialize an event tracker when the allocator
   // starts
@@ -547,6 +549,8 @@ class CacheAllocatorConfig {
   // from the bottom one if memory cache is full
   bool insertToFirstFreeTier = false;
 
+  bool noOnlineEviction = false;
+
   // the number of tries to search for an item to evict
   // 0 means it's infinite
   unsigned int evictionSearchTries{50};
@@ -687,6 +691,12 @@ CacheAllocatorConfig<T>& CacheAllocatorConfig<T>::enableInsertToFirstFreeTier()
   return *this;
 }
 
+template <typename T>
+CacheAllocatorConfig<T>& CacheAllocatorConfig<T>::enableNoOnlineEviction() {
+  noOnlineEviction = true;
+  return *this;
+}
+
 template <typename T>
 CacheAllocatorConfig<T>& CacheAllocatorConfig<T>::setCacheName(
     const std::string& _cacheName) {
@@ -1269,6 +1279,7 @@ std::map<std::string, std::string> CacheAllocatorConfig<T>::serialize() const {
   configMap["delayCacheWorkersStart"] =
       delayCacheWorkersStart ? "true" : "false";
   configMap["insertToFirstFreeTier"] = std::to_string(insertToFirstFreeTier);
+  configMap["noOnlineEviction"] = std::to_string(noOnlineEviction);
   mergeWithPrefix(configMap, throttleConfig.serialize(), "throttleConfig");
   mergeWithPrefix(configMap,
                   chainedItemAccessConfig.serialize(),

cachelib/cachebench/cache/Cache.h

@@ -579,6 +579,7 @@ Cache<Allocator>::Cache(const CacheConfig& config,
   }
 
   allocatorConfig_.insertToFirstFreeTier = config_.insertToFirstFreeTier;
+  allocatorConfig_.noOnlineEviction = config_.noOnlineEviction;
 
   auto cleanupGuard = folly::makeGuard([&] {
     if (!nvmCacheFilePath_.empty()) {

cachelib/cachebench/util/CacheConfig.cpp

@@ -51,6 +51,7 @@ CacheConfig::CacheConfig(const folly::dynamic& configJson) {
   JSONSetVal(configJson, useCombinedLockForIterators);
 
   JSONSetVal(configJson, insertToFirstFreeTier);
+  JSONSetVal(configJson, noOnlineEviction);
 
   JSONSetVal(configJson, lru2qHotPct);
   JSONSetVal(configJson, lru2qColdPct);

cachelib/cachebench/util/CacheConfig.h

@@ -99,6 +99,7 @@ struct CacheConfig : public JSONConfig {
   bool useCombinedLockForIterators{true};
 
   bool insertToFirstFreeTier{false};
+  bool noOnlineEviction{false};
 
   // LRU param
   uint64_t lruIpSpec{0};