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       1                 :             : // Copyright 2026 HPActor Contributors
       2                 :             : //
       3                 :             : // Licensed under the Apache License, Version 2.0 (the "License");
       4                 :             : // you may not use this file except in compliance with the License.
       5                 :             : // You may obtain a copy of the License at
       6                 :             : //
       7                 :             : //     http://www.apache.org/licenses/LICENSE-2.0
       8                 :             : //
       9                 :             : // Unless required by applicable law or agreed to in writing, software
      10                 :             : // distributed under the License is distributed on an "AS IS" BASIS,
      11                 :             : // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      12                 :             : // See the License for the specific language governing permissions and
      13                 :             : // limitations under the License.
      14                 :             : 
      15                 :             : #include <hpactor/mem/compaction.hpp>
      16                 :             : 
      17                 :             : #include <chrono>
      18                 :             : 
      19                 :             : namespace hpactor::mem {
      20                 :             : 
      21                 :           6 : bool CompactionManager::should_compact_slab(uint32_t live_blocks,
      22                 :             :                                              uint32_t total_blocks) const noexcept {
      23                 :           6 :     if (total_blocks == 0) return false;
      24                 :           5 :     float utilization = static_cast<float>(live_blocks)
      25                 :           5 :                         / static_cast<float>(total_blocks);
      26                 :           5 :     return utilization <= config_.compaction_threshold;
      27                 :             : }
      28                 :             : 
      29                 :             : CompactionManager::WasteReport
      30                 :           1 : CompactionManager::compute_waste(const SlabCache& cache) noexcept {
      31                 :           1 :     WasteReport report;
      32                 :             : 
      33                 :             :     // Waste = unused bytes in partially-filled slabs
      34                 :             :     // For simplicity: report stats from the cache's built-in counters
      35                 :           1 :     const auto& stats = cache.stats();
      36                 :           1 :     report.total_bytes = stats.alloc_count.load(std::memory_order_relaxed)
      37                 :           1 :                          * size_for_class(cache.size_class());
      38                 :             : 
      39                 :             :     // Estimate waste from freed blocks not yet recycled
      40                 :           1 :     uint64_t freed = stats.free_count.load(std::memory_order_relaxed);
      41                 :           1 :     uint64_t allocated = stats.alloc_count.load(std::memory_order_relaxed);
      42                 :           1 :     if (allocated > freed) {
      43                 :           1 :         uint64_t live = allocated - freed;
      44                 :             :         // Slabs have fixed total blocks; compute wasted space
      45                 :             :         // Blocks per slab for each size class (64KB base / block_size)
      46                 :             :         static constexpr uint32_t kSlabBlocks[kNumSizeClasses] = {
      47                 :             :             2048, 1024, 512, 512, 512, 256, 256, 128
      48                 :             :         };
      49                 :           1 :         uint64_t slab_blocks = kSlabBlocks[static_cast<uint8_t>(cache.size_class())];
      50                 :           1 :         uint64_t slabs_needed = (live + slab_blocks - 1) / slab_blocks;
      51                 :           1 :         uint64_t full_capacity = slabs_needed * slab_blocks
      52                 :           1 :                                  * size_for_class(cache.size_class());
      53                 :           1 :         report.wasted_bytes = (full_capacity > report.total_bytes)
      54                 :           1 :                               ? (full_capacity - report.total_bytes) : 0;
      55                 :             :     }
      56                 :             : 
      57                 :           1 :     if (report.total_bytes > 0) {
      58                 :           1 :         report.waste_ratio = static_cast<float>(report.wasted_bytes)
      59                 :           1 :                              / static_cast<float>(report.total_bytes);
      60                 :             :     }
      61                 :           1 :     return report;
      62                 :             : }
      63                 :             : 
      64                 :           2 : bool CompactionManager::should_compact() const noexcept {
      65                 :           2 :     auto now = std::chrono::steady_clock::now();
      66                 :           2 :     auto now_ms = std::chrono::duration_cast<std::chrono::milliseconds>(
      67                 :           4 :         now.time_since_epoch()).count();
      68                 :           2 :     return (now_ms - last_compaction_ts_)
      69                 :           2 :            >= static_cast<int64_t>(config_.compaction_interval_ms);
      70                 :             : }
      71                 :             : 
      72                 :           1 : void CompactionManager::record_compaction() noexcept {
      73                 :           1 :     auto now = std::chrono::steady_clock::now();
      74                 :           1 :     last_compaction_ts_ = std::chrono::duration_cast<std::chrono::milliseconds>(
      75                 :           2 :         now.time_since_epoch()).count();
      76                 :           1 : }
      77                 :             : 
      78                 :             : } // namespace hpactor::mem