Add memory usage statistics for slabs and allocation classes

Author: igchor

cachelib/allocator/PromotionStrategy.h

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed 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.
+ */
+
+#pragma once
+
+#include "cachelib/allocator/Cache.h"
+#include "cachelib/allocator/BackgroundEvictorStrategy.h"
+
+namespace facebook {
+namespace cachelib {
+
+
+// Base class for background eviction strategy.
+class PromotionStrategy : public BackgroundEvictorStrategy {
+
+public:
+  PromotionStrategy(uint64_t promotionAcWatermark, uint64_t maxPromotionBatch, uint64_t minPromotionBatch):
+  promotionAcWatermark(promotionAcWatermark), maxPromotionBatch(maxPromotionBatch), minPromotionBatch(minPromotionBatch)
+  {
+
+  }
+  ~PromotionStrategy() {}
+
+  std::vector<size_t> calculateBatchSizes(const CacheBase& cache,
+                                       std::vector<std::tuple<TierId, PoolId, ClassId>> acVec) {
+    std::vector<size_t> batches{};
+    for (auto [tid, pid, cid] : acVec) {
+      XDCHECK(tid > 0);
+      auto stats = cache.getAllocationClassStats(tid - 1, pid, cid);
+      if (stats.approxFreePercent < promotionAcWatermark)
+        batches.push_back(0);
+      else {
+        auto maxPossibleItemsToPromote = static_cast<size_t>((promotionAcWatermark - stats.approxFreePercent) *
+          stats.memorySize / stats.allocSize);
+        batches.push_back(maxPossibleItemsToPromote);
+      }
+    }
+
+    auto maxBatch = *std::max_element(batches.begin(), batches.end());
+    if (maxBatch == 0)
+      return batches;
+
+    std::transform(batches.begin(), batches.end(), batches.begin(), [&](auto numItems){
+      auto cappedBatchSize = maxPromotionBatch * numItems / maxBatch;
+      if (cappedBatchSize < minPromotionBatch)
+        return 0UL;
+      else
+        return cappedBatchSize;
+    });
+
+    return batches;
+  }
+private:
+  double promotionAcWatermark{4.0};
+  uint64_t maxPromotionBatch{40};
+  uint64_t minPromotionBatch{5};
+};
+
+} // namespace cachelib
+} // namespace facebook