Do not compensate for rounding error when calculating tier sizes (#43)

Compensation results in ratios being different than originially specified.

Author: igchor

cachelib/allocator/CacheAllocatorConfig.h

@@ -883,12 +883,6 @@ CacheAllocatorConfig<T>::getMemoryTierConfigs() const {
     sum_sizes += tier_config.getSize();
   }
 
-  if (size != sum_sizes) {
-    // Adjust capacity of the last tier to account for rounding error
-    config.back().setSize(
-      config.back().getSize() + (getCacheSize() - sum_sizes));
-  }
-
   return config;
 }
 

cachelib/allocator/tests/MemoryTiersTest.cpp

@@ -52,10 +52,11 @@ class MemoryTiersTest: public AllocatorTest<Allocator> {
       size_t sum_ratios = std::accumulate(configs.begin(), configs.end(), 0,
           [](const size_t i, const MemoryTierCacheConfig& config) { return i + config.getRatio();});
 
-      EXPECT_EQ(sum_sizes, expectedTotalCacheSize);
-      size_t partition_size = 0, remaining_capacity = actualConfig.getCacheSize();
+      size_t partition_size = 0;
       if (sum_ratios) {
         partition_size = actualConfig.getCacheSize() / sum_ratios;
+        /* Sum of sizes can be lower due to rounding down to partition_size. */
+        EXPECT_GE(sum_sizes, expectedTotalCacheSize - partition_size);
       }
 
       for(auto i = 0; i < configs.size(); ++i) {
@@ -65,10 +66,7 @@ class MemoryTiersTest: public AllocatorTest<Allocator> {
         if (configs[i].getRatio() && (i < configs.size() - 1)) {
           EXPECT_EQ(configs[i].getSize(), partition_size * configs[i].getRatio());
         }
-        remaining_capacity -= configs[i].getSize();
       }
-
-      EXPECT_EQ(remaining_capacity, 0);
     }
 
     LruAllocatorConfig createTestCacheConfig(