Add memory usage statistics for allocation classes

This includes printing:
- allocSize
- allocated memory size
- memory usage fraction

Author: igchor

cachelib/allocator/Cache.h

@@ -102,6 +102,12 @@ class CacheBase {
   // @param poolId   the pool id
   virtual PoolStats getPoolStats(PoolId poolId) const = 0;
 
+  // Get Allocation Class specific stats.
+  //
+  // @param poolId   the pool id
+  // @param classId   the class id
+  virtual ACStats getACStats(PoolId poolId, ClassId classId) const = 0;
+
   // @param poolId   the pool id
   virtual AllSlabReleaseEvents getAllSlabReleaseEvents(PoolId poolId) const = 0;
 

cachelib/allocator/CacheAllocator-inl.h

@@ -2372,6 +2372,14 @@ PoolStats CacheAllocator<CacheTrait>::getPoolStats(PoolId poolId) const {
   return ret;
 }
 
+template <typename CacheTrait>
+ACStats CacheAllocator<CacheTrait>::getACStats(PoolId poolId,
+                                               ClassId classId) const {
+  const auto& pool = allocator_->getPool(poolId);
+  const auto& ac = pool.getAllocationClass(classId);
+  return ac.getStats();
+}
+
 template <typename CacheTrait>
 PoolEvictionAgeStats CacheAllocator<CacheTrait>::getPoolEvictionAgeStats(
     PoolId pid, unsigned int slabProjectionLength) const {

cachelib/allocator/CacheAllocator.h

@@ -1214,6 +1214,9 @@ class CacheAllocator : public CacheBase {
   // return cache's memory usage stats
   CacheMemoryStats getCacheMemoryStats() const override final;
 
+  // return stats for Allocation Class
+  ACStats getACStats(PoolId pid, ClassId cid) const override final;
+
   // return the nvm cache stats map
   util::StatsMap getNvmCacheStatsMap() const override final;
 

cachelib/allocator/memory/MemoryAllocatorStats.h

@@ -56,6 +56,17 @@ struct ACStats {
   constexpr size_t getTotalFreeMemory() const noexcept {
     return Slab::kSize * freeSlabs + freeAllocs * allocSize;
   }
+
+  constexpr double usageFraction() const noexcept {
+    if (usedSlabs == 0)
+      return 0.0;
+
+    return activeAllocs / (usedSlabs * allocsPerSlab);
+  }
+
+  constexpr size_t totalAllocatedSize() const noexcept {
+    return activeAllocs * allocSize;
+  }
 };
 
 // structure to query stats corresponding to a MemoryPool

cachelib/allocator/tests/CacheBaseTest.cpp

@@ -34,6 +34,7 @@ class CacheBaseTest : public CacheBase, public SlabAllocatorTestBase {
   bool isObjectCache() const override { return false; }
   const MemoryPool& getPool(PoolId) const override { return memoryPool_; }
   PoolStats getPoolStats(PoolId) const override { return PoolStats(); }
+  ACStats getACStats(PoolId, ClassId) const { return ACStats(); };
   AllSlabReleaseEvents getAllSlabReleaseEvents(PoolId) const override {
     return AllSlabReleaseEvents{};
   }

cachelib/cachebench/cache/Cache.h

@@ -327,6 +327,10 @@ class Cache {
   // return the stats for the pool.
   PoolStats getPoolStats(PoolId pid) const { return cache_->getPoolStats(pid); }
 
+  ACStats getACStats(PoolId pid, ClassId cid) const {
+    return cache_->getACStats(pid, cid);
+  }
+
   // return the total number of inconsistent operations detected since start.
   unsigned int getInconsistencyCount() const {
     return inconsistencyCount_.load(std::memory_order_relaxed);

cachelib/cachebench/cache/CacheStats.h

@@ -194,7 +194,7 @@ struct Stats {
       foreachAC(allocationClassStats, [&](auto pid, auto cid, auto stats) {
         auto [allocSizeSuffix, allocSize] = formatMemory(stats.allocSize);
         auto [memorySizeSuffix, memorySize] =
-            formatMemory(stats.activeAllocs * stats.allocSize);
+            formatMemory(stats.totalAllocatedSize());
         out << folly::sformat("pid{:2} cid{:4} {:8.2f}{} memorySize: {:8.2f}{}",
                               pid, cid, allocSize, allocSizeSuffix, memorySize,
                               memorySizeSuffix)
@@ -206,15 +206,9 @@ struct Stats {
 
         // If the pool is not full, extrapolate usageFraction for AC assuming it
         // will grow at the same rate. This value will be the same for all ACs.
-        double acUsageFraction;
-        if (poolUsageFraction[pid] < 1.0) {
-          acUsageFraction = poolUsageFraction[pid];
-        } else if (stats.usedSlabs == 0) {
-          acUsageFraction = 0.0;
-        } else {
-          acUsageFraction =
-              stats.activeAllocs / (stats.usedSlabs * stats.allocsPerSlab);
-        }
+        auto acUsageFraction = (poolUsageFraction[pid] < 1.0)
+                                   ? poolUsageFraction[pid]
+                                   : stats.usageFraction();
 
         out << folly::sformat(
                    "pid{:2} cid{:4} {:8.2f}{} usageFraction: {:4.2f}", pid, cid,