chunk_allocator.h

#pragma once
#include "gaia/config/config.h"
 
#include <cinttypes>
#include <cstdint>
#include <cstring>
 
#include "gaia/cnt/fwd_llist.h"
#include "gaia/cnt/sarray.h"
#include "gaia/core/bit_utils.h"
#include "gaia/core/dyn_singleton.h"
#include "gaia/core/utility.h"
#include "gaia/mem/mem_alloc.h"
#include "gaia/util/logging.h"
 
namespace gaia {
  namespace ecs {
    namespace detail {
      struct MemoryBlockHeader final {
        uintptr_t m_pageAddr = 0;
        uint32_t m_reserved = 0;
#if GAIA_DEBUG
        uint32_t m_requestedBytes = 0;
#endif
      };
 
      class ChunkAllocatorImpl;
    } // namespace detail
 
    static constexpr uint32_t MemoryBlockAlignment = 64;
    static constexpr uint32_t MinMemoryBlockSize = 1024 * 8;
    static constexpr uint32_t MemoryBlockSizeClasses = 4;
    static constexpr uint32_t MaxMemoryBlockSize = UINT16_MAX & ~(MemoryBlockAlignment - 1);
    static constexpr uint32_t MemoryBlockUsableOffset = 40;
 
    constexpr uint16_t mem_block_size(uint32_t sizeType) {
      constexpr uint16_t sizes[] = {
          MinMemoryBlockSize, MinMemoryBlockSize * 2, MinMemoryBlockSize * 4, MaxMemoryBlockSize};
      return sizes[sizeType];
    }
 
    constexpr uint8_t mem_block_size_type(uint32_t sizeBytes) {
      GAIA_ASSERT(sizeBytes > 0);
      if (sizeBytes <= MinMemoryBlockSize)
        return 0;
      if (sizeBytes <= MinMemoryBlockSize * 2)
        return 1;
      if (sizeBytes <= MinMemoryBlockSize * 4)
        return 2;
      return 3;
    }
 
#if GAIA_ECS_CHUNK_ALLOCATOR
    struct GAIA_API ChunkAllocatorPageStats final {
      uint64_t mem_total;
      uint64_t mem_used;
      uint32_t num_pages;
      uint32_t num_pages_free;
  #if GAIA_DEBUG
      uint64_t mem_requested;
      uint32_t num_pages_empty;
  #endif
    };
 
    struct GAIA_API ChunkAllocatorStats final {
      ChunkAllocatorPageStats stats[MemoryBlockSizeClasses];
    };
 
    using ChunkAllocator = core::dyn_singleton<detail::ChunkAllocatorImpl>;
 
    namespace detail {
      static_assert(sizeof(MemoryBlockHeader) <= MemoryBlockUsableOffset);
 
      struct MemoryPageHeader {
        void* m_data;
 
        MemoryPageHeader(void* ptr): m_data(ptr) {}
      };
 
      struct MemoryPage: MemoryPageHeader, cnt::fwd_llist_base<MemoryPage> {
        static constexpr uint16_t NBlocks = 48;
        static constexpr uint16_t NBlocks_Bits = (uint16_t)core::count_bits(NBlocks);
        static constexpr uint32_t InvalidBlockId = NBlocks + 1;
  #if GAIA_DEBUG
        static constexpr uint8_t FreedBlockPattern = 0xDD;
  #endif
        static constexpr uint32_t BlockArrayBytes = ((uint32_t)NBlocks_Bits * (uint32_t)NBlocks + 7) / 8;
        using BlockArray = cnt::sarray<uint8_t, BlockArrayBytes>;
        using BitView = core::bit_view<NBlocks_Bits>;
 
        BlockArray m_blocks;
 
        uint32_t m_sizeType : 2;
        uint32_t m_blockCnt : NBlocks_Bits;
        uint32_t m_usedBlocks : NBlocks_Bits;
        uint32_t m_nextFreeBlock : NBlocks_Bits;
        uint32_t m_freeBlocks : NBlocks_Bits;
        // uint32_t m_unused : 6;
 
  #if GAIA_ASSERT_ENABLED
        uint64_t m_usedMask = 0;
  #endif
 
        MemoryPage(void* ptr, uint8_t sizeType):
            MemoryPageHeader(ptr), m_sizeType(sizeType), m_blockCnt(0), m_usedBlocks(0), m_nextFreeBlock(0),
            m_freeBlocks(0) {
  #if GAIA_ASSERT_ENABLED
          static_assert(sizeof(MemoryPage) <= 72);
  #else
          static_assert(sizeof(MemoryPage) <= 64);
  #endif
        }
 
        void write_block_idx(uint32_t blockIdx, uint32_t value) {
          const uint32_t bitPosition = blockIdx * NBlocks_Bits;
 
          GAIA_ASSERT(bitPosition < NBlocks * NBlocks_Bits);
          GAIA_ASSERT(value <= InvalidBlockId);
 
          BitView{{(uint8_t*)m_blocks.data(), BlockArrayBytes}}.set(bitPosition, (uint8_t)value);
        }
 
        uint8_t read_block_idx(uint32_t blockIdx) const {
          const uint32_t bitPosition = blockIdx * NBlocks_Bits;
 
          GAIA_ASSERT(bitPosition < NBlocks * NBlocks_Bits);
 
          return BitView{{(uint8_t*)m_blocks.data(), BlockArrayBytes}}.get(bitPosition);
        }
 
        GAIA_NODISCARD void* alloc_block(
  #if GAIA_DEBUG
            uint32_t bytesWanted
  #endif
        ) {
          auto StoreBlockAddress = [&](uint32_t index) {
            // Encode info about chunk's page in the memory block.
            // The actual pointer returned is offset by MemoryBlockUsableOffset bytes
            auto* pMemoryBlock = (uint8_t*)m_data + (index * mem_block_size(m_sizeType));
            GAIA_ASSERT((uintptr_t)pMemoryBlock % MemoryBlockAlignment == 0);
            auto& header = block_header(pMemoryBlock);
            header.m_pageAddr = (uintptr_t)this;
            header.m_reserved = 0;
  #if GAIA_DEBUG
            header.m_requestedBytes = bytesWanted;
  #endif
            return (void*)(pMemoryBlock + MemoryBlockUsableOffset);
          };
 
          // We don't want to go out of range for new blocks
          GAIA_ASSERT(!full() && "Trying to allocate too many blocks!");
 
          uint32_t index = 0;
          if (m_freeBlocks == 0U) {
            index = m_blockCnt;
            ++m_usedBlocks;
            ++m_blockCnt;
            write_block_idx(index, index);
          } else {
            GAIA_ASSERT(m_nextFreeBlock < m_blockCnt && "Block allocator recycle list broken!");
 
            ++m_usedBlocks;
            --m_freeBlocks;
 
            index = m_nextFreeBlock;
            m_nextFreeBlock = read_block_idx(m_nextFreeBlock);
          }
 
  #if GAIA_ASSERT_ENABLED
          GAIA_ASSERT((m_usedMask & (uint64_t(1) << index)) == 0 && "Block already marked as live");
          m_usedMask |= uint64_t(1) << index;
  #endif
 
          return StoreBlockAddress(index);
        }
 
        void free_block(void* pBlock) {
          GAIA_ASSERT(pBlock != nullptr);
          GAIA_ASSERT(m_usedBlocks > 0);
          GAIA_ASSERT(m_freeBlocks <= NBlocks);
 
          // Offset the chunk memory so we get the real block address
          const auto* pMemoryBlock = (uint8_t*)pBlock - MemoryBlockUsableOffset;
          const auto blckAddr = (uintptr_t)pMemoryBlock;
          GAIA_ASSERT(blckAddr % MemoryBlockAlignment == 0);
          const auto dataAddr = (uintptr_t)m_data;
          GAIA_ASSERT(blckAddr >= dataAddr);
          const auto blockSize = (uintptr_t)mem_block_size(m_sizeType);
  #if GAIA_ASSERT_ENABLED
          const auto pageSize = blockSize * NBlocks;
          GAIA_ASSERT(blckAddr < dataAddr + pageSize);
  #endif
          GAIA_ASSERT((blckAddr - dataAddr) % blockSize == 0);
          const auto blockIdx = (uint32_t)((blckAddr - dataAddr) / blockSize);
          GAIA_ASSERT(blockIdx < m_blockCnt);
 
  #if GAIA_DEBUG
          auto& header = block_header((void*)pMemoryBlock);
          GAIA_ASSERT(header.m_requestedBytes > 0);
  #endif
  #if GAIA_ASSERT_ENABLED
          GAIA_ASSERT((m_usedMask & (uint64_t(1) << blockIdx)) != 0 && "Double free or corrupted block state");
          m_usedMask &= ~(uint64_t(1) << blockIdx);
  #endif
 
  #if GAIA_DEBUG
          header.m_requestedBytes = 0;
          std::memset(pBlock, FreedBlockPattern, blockSize - MemoryBlockUsableOffset);
  #endif
 
          // Update our implicit list
          if (m_freeBlocks == 0U)
            write_block_idx(blockIdx, InvalidBlockId);
          else
            write_block_idx(blockIdx, m_nextFreeBlock);
          m_nextFreeBlock = blockIdx;
 
          ++m_freeBlocks;
          --m_usedBlocks;
        }
 
        GAIA_NODISCARD uint32_t used_blocks_cnt() const {
          return m_usedBlocks;
        }
 
        GAIA_NODISCARD bool full() const {
          return used_blocks_cnt() >= NBlocks;
        }
 
        GAIA_NODISCARD bool empty() const {
          return used_blocks_cnt() == 0;
        }
 
        void verify() const {
  #if GAIA_ASSERT_ENABLED
          GAIA_ASSERT(m_sizeType < MemoryBlockSizeClasses);
          GAIA_ASSERT(m_blockCnt <= NBlocks);
          GAIA_ASSERT(m_usedBlocks <= m_blockCnt);
          GAIA_ASSERT(m_freeBlocks <= m_blockCnt);
          GAIA_ASSERT(m_usedBlocks + m_freeBlocks == m_blockCnt);
 
          const auto blockSize = (uintptr_t)mem_block_size(m_sizeType);
 
          const auto pageAddr = (uintptr_t)m_data;
          GAIA_ASSERT(pageAddr % MemoryBlockAlignment == 0);
 
    #if GAIA_DEBUG
          uint64_t freeMask = 0;
    #endif
 
          if (m_freeBlocks != 0) {
            uint32_t next = m_nextFreeBlock;
            GAIA_FOR(m_freeBlocks) {
              GAIA_ASSERT(next < m_blockCnt);
    #if GAIA_DEBUG
              const auto bit = uint64_t(1) << next;
              GAIA_ASSERT((freeMask & bit) == 0 && "Free list contains a cycle");
              freeMask |= bit;
    #endif
              next = read_block_idx(next);
            }
 
            GAIA_ASSERT(next == InvalidBlockId);
          }
 
          GAIA_FOR(m_blockCnt) {
            const auto* pMemoryBlock = (const uint8_t*)m_data + (i * blockSize);
            const auto& header = block_header(pMemoryBlock);
            GAIA_ASSERT(header.m_pageAddr == (uintptr_t)this);
            GAIA_ASSERT(((uintptr_t)pMemoryBlock % MemoryBlockAlignment) == 0);
 
    #if GAIA_DEBUG
            const bool isFree = (freeMask & (uint64_t(1) << i)) != 0;
            GAIA_ASSERT((header.m_requestedBytes == 0) == isFree);
    #endif
          }
 
    #if GAIA_DEBUG
          GAIA_ASSERT((m_usedMask & freeMask) == 0);
          const auto liveMask = m_blockCnt == 64 ? ~uint64_t(0) : ((uint64_t(1) << m_blockCnt) - 1);
          GAIA_ASSERT((m_usedMask | freeMask) == liveMask);
    #endif
  #endif
        }
 
  #if GAIA_DEBUG
        GAIA_NODISCARD uint64_t requested_bytes() const {
          if (m_usedBlocks == 0)
            return 0;
 
          uint64_t freeMask = 0;
          uint32_t next = m_nextFreeBlock;
          GAIA_FOR(m_freeBlocks) {
            GAIA_ASSERT(next < m_blockCnt);
            const auto bit = uint64_t(1) << next;
            GAIA_ASSERT((freeMask & bit) == 0 && "Free list contains a cycle");
            freeMask |= bit;
            next = read_block_idx(next);
          }
 
          uint64_t requested = 0;
          GAIA_FOR(m_blockCnt) {
            if ((freeMask & (uint64_t(1) << i)) != 0)
              continue;
 
            const auto* pMemoryBlock = (const uint8_t*)m_data + (i * mem_block_size(m_sizeType));
            requested += block_header(pMemoryBlock).m_requestedBytes;
          }
 
          return requested;
        }
  #endif
 
      private:
        static MemoryBlockHeader& block_header(void* pMemoryBlock) {
          return *(MemoryBlockHeader*)pMemoryBlock;
        }
 
        static const MemoryBlockHeader& block_header(const void* pMemoryBlock) {
          return *(const MemoryBlockHeader*)pMemoryBlock;
        }
      };
 
      enum class MemoryPageState : uint8_t { Detached, Empty, Partial, Full };
 
      struct MemoryPageContainer {
        cnt::fwd_llist<MemoryPage> pagesEmpty;
        cnt::fwd_llist<MemoryPage> pagesPartial;
        cnt::fwd_llist<MemoryPage> pagesFull;
 
        GAIA_NODISCARD bool empty() const {
          return pagesEmpty.empty() && pagesPartial.empty() && pagesFull.empty();
        }
      };
 
      class ChunkAllocatorImpl {
        friend ::gaia::ecs::ChunkAllocator;
 
        MemoryPageContainer m_pages[MemoryBlockSizeClasses];
 
        bool m_isDone = false;
 
      private:
        ChunkAllocatorImpl() = default;
 
        void on_delete() {
          flush(true);
 
          // Make sure there are no leaks
          auto memStats = stats();
          for (const auto& s: memStats.stats) {
            if (s.mem_total != 0) {
              GAIA_ASSERT2(false, "ECS leaking memory");
              GAIA_LOG_W("ECS leaking memory!");
              diag();
            }
          }
        }
 
      public:
        ~ChunkAllocatorImpl() {
          on_delete();
        }
 
        ChunkAllocatorImpl(ChunkAllocatorImpl&& world) = delete;
        ChunkAllocatorImpl(const ChunkAllocatorImpl& world) = delete;
        ChunkAllocatorImpl& operator=(ChunkAllocatorImpl&&) = delete;
        ChunkAllocatorImpl& operator=(const ChunkAllocatorImpl&) = delete;
 
        void* alloc(uint32_t bytesWanted) {
          GAIA_ASSERT(bytesWanted > 0);
          GAIA_ASSERT(bytesWanted <= MaxMemoryBlockSize);
          if (bytesWanted == 0 || bytesWanted > MaxMemoryBlockSize)
            return nullptr;
 
          const auto sizeType = mem_block_size_type(bytesWanted);
          auto& container = m_pages[sizeType];
 
          MemoryPageState prevState = MemoryPageState::Partial;
          auto* pPage = container.pagesPartial.first;
          if (pPage == nullptr) {
            prevState = MemoryPageState::Empty;
            pPage = container.pagesEmpty.first;
            if (pPage == nullptr) {
              prevState = MemoryPageState::Detached;
              pPage = alloc_page(sizeType);
            }
          }
 
          // Allocate a new chunk of memory
  #if GAIA_DEBUG
          void* pBlock = pPage->alloc_block(bytesWanted);
  #else
          void* pBlock = pPage->alloc_block();
  #endif
 
          move_page(container, pPage, prevState, state_for(*pPage));
          verify();
          return pBlock;
        }
 
        GAIA_CLANG_WARNING_PUSH()
        // Memory is aligned so we can silence this warning
        GAIA_CLANG_WARNING_DISABLE("-Wcast-align")
 
        void free(void* pBlock) {
          GAIA_ASSERT(pBlock != nullptr);
          if (pBlock == nullptr)
            return;
 
          // Decode the page from the address
          const auto& header = *(const MemoryBlockHeader*)((uint8_t*)pBlock - MemoryBlockUsableOffset);
          const auto pageAddr = header.m_pageAddr;
          GAIA_ASSERT(pageAddr % sizeof(uintptr_t) == 0);
  #if GAIA_DEBUG
          GAIA_ASSERT(header.m_requestedBytes > 0);
  #endif
          auto* pPage = (MemoryPage*)pageAddr;
          const auto prevState = state_for(*pPage);
 
          auto& container = m_pages[pPage->m_sizeType];
 
  #if GAIA_ASSERT_ENABLED
          if (prevState == MemoryPageState::Full) {
            const auto res = container.pagesFull.has(pPage);
            GAIA_ASSERT(res && "Memory page couldn't be found among full pages");
          } else if (prevState == MemoryPageState::Partial) {
            const auto res = container.pagesPartial.has(pPage);
            GAIA_ASSERT(res && "Memory page couldn't be found among partial pages");
          } else {
            GAIA_ASSERT(false && "Allocated block can't belong to an empty page");
          }
  #endif
 
          // Free the chunk
          pPage->free_block(pBlock);
 
          // Update lists
          move_page(container, pPage, prevState, state_for(*pPage));
          verify();
 
          // Special handling for the allocator signaled to destroy itself
          if (m_isDone) {
            if (pPage->empty()) {
              container.pagesEmpty.unlink(pPage);
              free_page(pPage);
            }
 
            try_delete_this();
          }
        }
 
        GAIA_CLANG_WARNING_POP()
 
        
        ChunkAllocatorStats stats() const {
          ChunkAllocatorStats stats{};
          for (uint32_t sizeType = 0; sizeType < MemoryBlockSizeClasses; ++sizeType)
            stats.stats[sizeType] = page_stats(sizeType);
          return stats;
        }
 
        void flush(bool releaseAll = false) {
          uint32_t i = 0;
          for (auto& page: m_pages)
            flushPages(page, i++, releaseAll);
          verify();
        }
 
        void diag() const {
          auto diagPage = [](const ChunkAllocatorPageStats& stats, uint32_t sizeType) {
            GAIA_LOG_N("ChunkAllocator %uK stats", mem_block_size(sizeType) / 1024);
            GAIA_LOG_N("  Allocated: %" PRIu64 " B", stats.mem_total);
            GAIA_LOG_N("  Reserved by live blocks: %" PRIu64 " B", stats.mem_used);
            GAIA_LOG_N("  Pages: %u", stats.num_pages);
            GAIA_LOG_N("  Reusable pages: %u", stats.num_pages_free);
  #if !GAIA_DEBUG
            GAIA_LOG_N(
                "  Utilization: %.1f%%",
                stats.mem_total ? 100.0 * ((double)stats.mem_used / (double)stats.mem_total) : 0);
  #else
            GAIA_LOG_N("  Requested: %" PRIu64 " B", stats.mem_requested);
            GAIA_LOG_N("  Free capacity: %" PRIu64 " B", stats.mem_total - stats.mem_used);
            GAIA_LOG_N("  Internal slack: %" PRIu64 " B", stats.mem_used - stats.mem_requested);
            GAIA_LOG_N(
                "  Utilization: %.1f%%",
                stats.mem_total ? 100.0 * ((double)stats.mem_requested / (double)stats.mem_total) : 0);
            GAIA_LOG_N("  Empty pages: %u", stats.num_pages_empty);
  #endif
          };
 
          auto memStats = stats();
          for (uint32_t sizeType = 0; sizeType < MemoryBlockSizeClasses; ++sizeType)
            diagPage(memStats.stats[sizeType], sizeType);
        }
 
        void verify() const {
  #if GAIA_ASSERT_ENABLED
          for (uint32_t sizeType = 0; sizeType < MemoryBlockSizeClasses; ++sizeType)
            verify_container(m_pages[sizeType], sizeType);
  #endif
        }
 
      private:
        static constexpr const char* s_strChunkAlloc_Chunk = "Chunk";
        static constexpr const char* s_strChunkAlloc_MemPage = "MemoryPage";
 
        static MemoryPage* alloc_page(uint8_t sizeType) {
          const uint32_t size = mem_block_size(sizeType) * MemoryPage::NBlocks;
          auto* pPageData = mem::AllocHelper::alloc_alig<uint8_t>(s_strChunkAlloc_Chunk, MemoryBlockAlignment, size);
          auto* pMemoryPage = mem::AllocHelper::alloc<MemoryPage>(s_strChunkAlloc_MemPage);
          return new (pMemoryPage) MemoryPage(pPageData, sizeType);
        }
 
        static void free_page(MemoryPage* pMemoryPage) {
          GAIA_ASSERT(pMemoryPage != nullptr);
 
          mem::AllocHelper::free_alig(s_strChunkAlloc_Chunk, pMemoryPage->m_data);
          pMemoryPage->~MemoryPage();
          mem::AllocHelper::free(s_strChunkAlloc_MemPage, pMemoryPage);
        }
 
        void done() {
          m_isDone = true;
        }
 
        void try_delete_this() {
          // When there is nothing left, delete the allocator
          bool allEmpty = true;
          for (const auto& c: m_pages)
            allEmpty = allEmpty && c.empty();
          if (allEmpty)
            delete this;
        }
 
        static constexpr uint32_t warm_pages_to_keep(uint32_t sizeType) {
          constexpr uint8_t WarmPagesPerSizeClass[] = {1, 1, 0, 0};
          return WarmPagesPerSizeClass[sizeType];
        }
 
        static MemoryPageState state_for(const MemoryPage& page) {
          if (page.empty())
            return MemoryPageState::Empty;
          if (page.full())
            return MemoryPageState::Full;
          return MemoryPageState::Partial;
        }
 
        static cnt::fwd_llist<MemoryPage>& page_list(MemoryPageContainer& container, MemoryPageState state) {
          switch (state) {
            case MemoryPageState::Empty:
              return container.pagesEmpty;
            case MemoryPageState::Partial:
              return container.pagesPartial;
            default:
              GAIA_ASSERT(state == MemoryPageState::Full);
              return container.pagesFull;
          }
        }
 
        static void move_page(
            MemoryPageContainer& container, MemoryPage* pPage, MemoryPageState fromState, MemoryPageState toState) {
          if (fromState == toState)
            return;
 
          if (fromState != MemoryPageState::Detached)
            page_list(container, fromState).unlink(pPage);
          page_list(container, toState).link(pPage);
        }
 
        [[maybe_unused]] static void verify_page_membership(
            [[maybe_unused]] const MemoryPageContainer& container, //
            [[maybe_unused]] const MemoryPage& page, //
            [[maybe_unused]] MemoryPageState expectedState //
        ) {
          (void)container;
          GAIA_ASSERT(state_for(page) == expectedState);
          GAIA_ASSERT(page.get_fwd_llist_link().linked());
        }
 
        static void verify_container(const MemoryPageContainer& container, uint32_t sizeType) {
          (void)sizeType;
          for (const auto& page: container.pagesEmpty) {
            GAIA_ASSERT(page.m_sizeType == sizeType);
            verify_page_membership(container, page, MemoryPageState::Empty);
            page.verify();
          }
 
          for (const auto& page: container.pagesPartial) {
            GAIA_ASSERT(page.m_sizeType == sizeType);
            verify_page_membership(container, page, MemoryPageState::Partial);
            page.verify();
          }
 
          for (const auto& page: container.pagesFull) {
            GAIA_ASSERT(page.m_sizeType == sizeType);
            verify_page_membership(container, page, MemoryPageState::Full);
            page.verify();
          }
        }
 
        ChunkAllocatorPageStats page_stats(uint32_t sizeType) const {
          ChunkAllocatorPageStats stats{};
          const auto& container = m_pages[sizeType];
          const auto blockSize = (uint64_t)mem_block_size(sizeType);
          const auto pageSize = blockSize * MemoryPage::NBlocks;
 
          stats.num_pages = (uint32_t)container.pagesEmpty.size() + (uint32_t)container.pagesPartial.size() +
                            (uint32_t)container.pagesFull.size();
          stats.num_pages_free = (uint32_t)container.pagesEmpty.size() + (uint32_t)container.pagesPartial.size();
          stats.mem_total = stats.num_pages * pageSize;
          stats.mem_used = container.pagesFull.size() * pageSize;
 
  #if GAIA_DEBUG
          stats.num_pages_empty = (uint32_t)container.pagesEmpty.size();
 
          for (const auto& page: container.pagesFull)
            stats.mem_requested += page.requested_bytes();
 
          for (const auto& page: container.pagesPartial) {
            stats.mem_used += page.used_blocks_cnt() * blockSize;
            stats.mem_requested += page.requested_bytes();
          }
  #else
          for (const auto& page: container.pagesPartial)
            stats.mem_used += page.used_blocks_cnt() * blockSize;
  #endif
 
          return stats;
        }
 
        void flushPages(MemoryPageContainer& container, uint32_t sizeType, bool releaseAll) {
          const bool keepWarmPage = !releaseAll && warm_pages_to_keep(sizeType) != 0;
          bool keptWarmPage = false;
          for (auto it = container.pagesEmpty.begin(); it != container.pagesEmpty.end();) {
            auto* pPage = &(*it);
            ++it;
 
            // Skip non-empty pages
            if (!pPage->empty())
              continue;
 
            if (keepWarmPage && !keptWarmPage) {
              keptWarmPage = true;
              continue;
            }
 
            container.pagesEmpty.unlink(pPage);
            free_page(pPage);
          }
        }
      };
    } // namespace detail
 
#endif
 
  } // namespace ecs
} // namespace gaia