2026-09-25 13:00:48

Signed-off-by: lizzie <lizzie@eden-emu.dev>

src/common/sparse_large_vector.cpp

@@ -8,7 +8,14 @@
 #ifdef _WIN32
 #include <windows.h>
 #include <mutex>
-#else
+#include <algorithm>
+#include <vector>
+#endif
+
+#include <cerrno>
+#include <cstring>
+
+#ifndef _WIN32
 #include <sys/mman.h>
 #endif
 
@@ -19,54 +26,60 @@
 namespace Common {
 
 #ifdef _WIN32
-static std::vector<std::pair<u64, u64>> vector_regions {};
 
-// Workaround for handling non-commited memory accessed by Dynarmic; usually result of an error
+struct VectorRegion {
+    u64 start_page;
+    u64 end_page;
+};
+
+static std::mutex& GetVectorRegionsMutex() {
+    static std::mutex* m = new std::mutex();
+    return *m;
+}
+
+static std::vector<VectorRegion>& GetVectorRegions() {
+    static std::vector<VectorRegion>* v = new std::vector<VectorRegion>();
+    return *v;
+}
+
 static LONG WINAPI FakePageFaultHandler(PEXCEPTION_POINTERS info) {
-    DWORD code = info->ExceptionRecord->ExceptionCode;
-    u64 exception_addr = reinterpret_cast<u64>(info->ExceptionRecord->ExceptionAddress);
-
-    if (code != EXCEPTION_ACCESS_VIOLATION) {
-        // Not our problem
+    if (info->ExceptionRecord->ExceptionCode != EXCEPTION_ACCESS_VIOLATION) {
         return EXCEPTION_CONTINUE_SEARCH;
     }
 
-    u64 addr = 0, addr2 = 0;
+    const u64 fault_addr = info->ExceptionRecord->ExceptionInformation[1];
+    const u64 access_type = info->ExceptionRecord->ExceptionInformation[0];
+    const bool is_write = (access_type == 1);
+    const u64 fault_page = fault_addr >> HostPageBits;
 
-    for (auto region: vector_regions) {
-        auto addr_shifted = exception_addr >> HostPageBits;
-        if (region.first <= addr_shifted && addr_shifted <= region.second) {
-            addr = addr_shifted;
-        }
+    u64 addr = 0;
+    u64 addr2 = 0;
 
-        // Page-boundary accesses
-        if (auto addr_ = (exception_addr + 0x40) >> HostPageBits; addr_ != addr_shifted && region.first <= addr_ && addr_ <= region.second) {
-            addr2 = addr_;
-        }
-
-        if (addr != 0 || addr2 != 0) {
-            break;
+    {
+        std::lock_guard lock(GetVectorRegionsMutex());
+        for (const auto& region : GetVectorRegions()) {
+            if (fault_page >= region.start_page && fault_page < region.end_page) {
+                addr = fault_page;
+            }
+            const u64 page2 = (fault_addr + 0x3F) >> HostPageBits;
+            if (page2 != fault_page && page2 >= region.start_page && page2 < region.end_page) {
+                addr2 = page2;
+            }
+            if (addr != 0 || addr2 != 0) break;
         }
     }
 
     if (addr == 0 && addr2 == 0) {
-        // Not our problem
         return EXCEPTION_CONTINUE_SEARCH;
     }
 
-    LOG_ERROR(HW_Memory, "Accessing an unallocated region of a SparseLargeVector at {:#x}; this shouldn't happen and is likely a Dynarmic error!", exception_addr);
+    LOG_ERROR(HW_Memory, "Accessing an unallocated region of a SparseLargeVector at {:#x}; this shouldn't happen and is likely a Dynarmic error!", fault_addr);
 
-    // Commit this region
-    if (addr != 0) {
-        if (!CommitVectorPage(addr << HostPageBits, false)) {
-            return EXCEPTION_CONTINUE_SEARCH;
-        }
+    if (addr != 0 && !CommitVectorPage(addr << HostPageBits, is_write)) {
+        return EXCEPTION_CONTINUE_SEARCH;
     }
-    // Commit next region if needed
-    if (addr2 != 0) {
-        if (!CommitVectorPage(addr2 << HostPageBits, false)) {
-            return EXCEPTION_CONTINUE_SEARCH;
-        }
+    if (addr2 != 0 && !CommitVectorPage(addr2 << HostPageBits, is_write)) {
+        return EXCEPTION_CONTINUE_SEARCH;
     }
 
     return EXCEPTION_CONTINUE_EXECUTION;
@@ -74,23 +87,31 @@ static LONG WINAPI FakePageFaultHandler(PEXCEPTION_POINTERS info) {
 
 bool CommitVectorPage(uintptr_t addr, bool write) noexcept {
     MEMORY_BASIC_INFORMATION info {};
-    auto res = VirtualQuery(reinterpret_cast<void*>(addr), &info, sizeof(info));
+    const auto res = VirtualQuery(reinterpret_cast<void*>(addr), &info, sizeof(info));
+    const DWORD perm = write ? PAGE_READWRITE : PAGE_READONLY;
+
     if (res == 0) {
         LOG_CRITICAL(HW_Memory, "Failed to query large buffer region at {:#x} with error {}, will try committing anyway", addr, GetLastError());
+    } else if (info.State == MEM_COMMIT) {
+        DWORD old_protect {};
+        if (!VirtualProtect(reinterpret_cast<void*>(addr), HostPageSize, perm, &old_protect)) {
+            LOG_ERROR(HW_Memory, "VirtualProtect failed at {:#x}, error {}", addr, GetLastError());
+            return false;
+        }
+        return true;
     } else if (info.State != MEM_RESERVE) {
-        LOG_ERROR(HW_Memory, "Tried to commit an unreserved large buffer region at {:#x} that is not mapped or is already committed (state {:#x})", addr, info.State);
+        LOG_ERROR(HW_Memory, "Tried to commit an unreserved large buffer region at {:#x} (state {:#x})", addr, info.State);
         return false;
     }
 
-    auto perm = write ? PAGE_READWRITE : PAGE_READONLY;
-    void* res2 = VirtualAlloc(reinterpret_cast<LPVOID>(addr), HostPageSize, MEM_COMMIT, perm);
-    if (res2 == nullptr) {
+    if (VirtualAlloc(reinterpret_cast<LPVOID>(addr), HostPageSize, MEM_COMMIT, perm) == nullptr) {
         LOG_ERROR(HW_Memory, "Failed to commit large buffer region at {:#x}, error {}", addr, GetLastError());
         return false;
     }
 
     return true;
 }
+
 #endif
 
 #ifndef MAP_NOCORE
@@ -102,57 +123,103 @@ bool CommitVectorPage(uintptr_t addr, bool write) noexcept {
 
 void DecommitVectorPage(uintptr_t base) noexcept {
 #if defined(_WIN32)
-    VirtualFree(reinterpret_cast<LPVOID>(base), HostPageSize, MEM_DECOMMIT);
+    if (!VirtualFree(reinterpret_cast<LPVOID>(base), HostPageSize, MEM_DECOMMIT)) {
+        LOG_WARNING(HW_Memory, "VirtualFree(MEM_DECOMMIT) failed at {:#x}, error {}", base, GetLastError());
+    }
 #elif defined(__linux__)
-    // Linux's MADV_DONTNEED zeros out pages for us
-    madvise(reinterpret_cast<void*>(base), HostPageSize, MADV_DONTNEED);
+    if (madvise(reinterpret_cast<void*>(base), HostPageSize, MADV_DONTNEED) != 0) {
+        LOG_WARNING(HW_Memory, "madvise(MADV_DONTNEED) failed at {:#x}: {}", base, std::strerror(errno));
+    }
 #else
-    madvise(reinterpret_cast<void*>(base), HostPageSize, MADV_FREE);
+    if (madvise(reinterpret_cast<void*>(base), HostPageSize, MADV_FREE) != 0) {
+        LOG_WARNING(HW_Memory, "madvise(MADV_FREE) failed at {:#x}: {}", base, std::strerror(errno));
+    }
     std::memset(reinterpret_cast<void*>(base), 0, HostPageSize);
 #endif
 }
 
 void* AllocateMemoryPages(std::size_t size) noexcept {
-    if (auto page = HostPageSize; size % page != 0) {
+    if (size == 0) {
+        return nullptr;
+    }
+
+    const auto page = HostPageSize;
+    if (size % page != 0) {
         LOG_WARNING(HW_Memory, "Allocating unaligned large vector with size {:#x}; aligning to {} page size", size, page);
+        if (size > SIZE_MAX - (page - 1)) {
+            LOG_CRITICAL(HW_Memory, "Size {:#x} would overflow page alignment", size);
+            return nullptr;
+        }
         size = AlignUp(size, page);
     }
 
 #ifdef _WIN32
-    // We will never use this memory entirely so instead of committing it up front let's just reserve it and commit each page individually
     void* base = VirtualAlloc(nullptr, size, MEM_RESERVE, PAGE_READWRITE);
 
     if (base != nullptr) {
-        vector_regions.emplace_back(reinterpret_cast<u64>(base), reinterpret_cast<u64>(base) + size);
+        {
+            std::lock_guard lock(GetVectorRegionsMutex());
+            GetVectorRegions().push_back({
+                reinterpret_cast<u64>(base) >> HostPageBits,
+                (reinterpret_cast<u64>(base) + size) >> HostPageBits,
+            });
+        }
 
         static std::once_flag flag;
         std::call_once(flag, []() { AddVectoredExceptionHandler(1, FakePageFaultHandler); });
     } else {
-        // Try committing everything instead??
         LOG_WARNING(HW_Memory, "Failed to reserve large vector region with error {}, trying to commit instead..", GetLastError());
         base = VirtualAlloc(nullptr, size, MEM_COMMIT, PAGE_READWRITE);
     }
     ASSERT_MSG(base, "Failed to reserve {:#x} sized region with error {}", size, GetLastError());
 #else
-    void* base = mmap(nullptr, size, PROT_READ, MAP_ANON | MAP_PRIVATE | MAP_NOCORE, -1, 0);
-    if (base == MAP_FAILED)
-        base = nullptr;
-    ASSERT_MSG(base, "Failed to allocate {:#x} sized region with error {}", size, strerror(errno));
+    int flags = MAP_ANON | MAP_PRIVATE;
+#ifdef MAP_NORESERVE
+    flags |= MAP_NORESERVE;
 #endif
+#if defined(MAP_NOCORE)
+    flags |= MAP_NOCORE;
+#endif
+    void* base = mmap(nullptr, size, PROT_READ, flags, -1, 0);
+    if (base == MAP_FAILED) {
+        base = nullptr;
+    }
+#ifdef MADV_HUGEPAGE
+    if (base != nullptr) {
+        madvise(base, size, MADV_HUGEPAGE);
+    }
+#endif
+    ASSERT_MSG(base, "Failed to allocate {:#x} sized region with error {}", size, std::strerror(errno));
+#endif
+
     return base;
 }
 
 void FreeMemoryPages(void* base, [[maybe_unused]] std::size_t size) noexcept {
-    if (auto page = HostPageSize; size % page != 0) {
+    if (base == nullptr) {
+        return;
+    }
+
+    if (const auto page = HostPageSize; size % page != 0) {
         size = AlignUp(size, page);
     }
-    if (!base)
-        return;
+
 #ifdef _WIN32
-    ASSERT(VirtualFree(base, 0, MEM_RELEASE));
+    {
+        std::lock_guard lock(GetVectorRegionsMutex());
+        auto& regions = GetVectorRegions();
+        const u64 base_page = reinterpret_cast<u64>(base) >> HostPageBits;
+        regions.erase(std::remove_if(regions.begin(), regions.end(),
+            [base_page](const VectorRegion& r) { return r.start_page == base_page; }), regions.end());
+    }
+    if (!VirtualFree(base, 0, MEM_RELEASE)) {
+        LOG_ERROR(HW_Memory, "VirtualFree failed, error {}", GetLastError());
+    }
 #else
-    ASSERT(munmap(base, size) == 0);
+    if (munmap(base, size) != 0) {
+        LOG_ERROR(HW_Memory, "munmap failed: {}", std::strerror(errno));
+    }
 #endif
 }
 
-} // namespace Common
+} // namespace Common

src/common/sparse_large_vector.h

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 /* virtual_buffer.h */
@@ -7,10 +7,14 @@
 
 #pragma once
 
+#include <array>
 #include <atomic>
 #include <bit>
-#include <utility>
-#include <vector>
+#include <cerrno>
+#include <cstdlib>
+#include <cstring>
+#include <memory>
+#include <type_traits>
 
 #ifndef _WIN32
 #include <unistd.h>
@@ -28,9 +32,9 @@ constexpr u64 HostPageBits = 12;
 constexpr u64 HostPageMask = ~(HostPageSize - 1);
 bool CommitVectorPage(uintptr_t addr, bool write) noexcept;
 #else
-const u64 HostPageSize = sysconf(_SC_PAGESIZE);
-const u64 HostPageBits = std::countr_zero(HostPageSize);
-const u64 HostPageMask = ~(HostPageSize - 1);
+inline const u64 HostPageSize = static_cast<u64>(sysconf(_SC_PAGESIZE));
+inline const u64 HostPageBits = std::countr_zero(HostPageSize);
+inline const u64 HostPageMask = ~(HostPageSize - 1);
 #endif
 
 void* AllocateMemoryPages(std::size_t size) noexcept;
@@ -43,20 +47,18 @@ template <typename T>
     // requires std::is_trivially_copyable_v<T>
 class SparseLargeVector final {
 public:
-    constexpr SparseLargeVector() = default;
+    SparseLargeVector() = default;
 
-    explicit SparseLargeVector(std::size_t count) noexcept
-        : alloc_size{count * sizeof(T)}
-    {
-        base_ptr = static_cast<T*>(AllocateMemoryPages(alloc_size));
-
-        // each item in vector holds information for 64 pages
-        auto denom = HostPageSize * 64;
-        committed_pages = std::vector<std::atomic<u64>>((alloc_size + denom - 1) / denom);
+    explicit SparseLargeVector(std::size_t count) noexcept {
+        if (count > SIZE_MAX / sizeof(T)) {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector size overflow: {} elements", count);
+            return;
+        }
+        Allocate(count * sizeof(T));
     }
 
     ~SparseLargeVector() noexcept {
-        FreeMemoryPages(base_ptr, alloc_size);
+        Release();
     }
 
     SparseLargeVector(const SparseLargeVector&) = delete;
@@ -65,145 +67,181 @@ public:
     SparseLargeVector& operator=(SparseLargeVector&& other) = delete;
 
     void ResizeAndClear(std::size_t count) noexcept {
-        if (auto const new_size = count * sizeof(T); new_size != alloc_size) {
-            FreeMemoryPages(base_ptr, alloc_size);
-            alloc_size = new_size;
-            base_ptr = static_cast<T*>(AllocateMemoryPages(alloc_size));
-
-            auto denom = HostPageSize * 64;
-            committed_pages = std::vector<std::atomic<u64>>((alloc_size + denom - 1) / denom);
+        if (count > SIZE_MAX / sizeof(T)) {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector resize overflow: {} elements", count);
+            return;
         }
+        const std::size_t new_size = count * sizeof(T);
+        if (new_size == alloc_size) {
+            ZeroRegion(0, alloc_size / sizeof(T));
+            return;
+        }
+        Release();
+        Allocate(new_size);
     }
 
-    /// Returns a reference to the value of the requested index and allocates memory if needed.
     T& GetAndFault(std::size_t index) noexcept {
-        if (index > alloc_size / sizeof(T)) {
-            UNREACHABLE_MSG("Out of bounds RW access on SparseLargeVector @ {}", index);
+        if (base_ptr == nullptr || index >= size()) [[unlikely]] {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector RW access out of bounds @ {} (size {})", index, size());
+            std::abort();
         }
-
-        if (!IsCommittedPage(index)) {
-            CommitPage(index);
+        const u64 byte_offset = static_cast<u64>(index) * sizeof(T);
+        if (!CommitPage(byte_offset)) [[unlikely]] {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector commit failed @ {} (offset {:#x})", index, byte_offset);
+            std::abort();
         }
         return base_ptr[index];
     }
 
-    /// Returns a reference to the value of the requested index if initialized, or will otherwise return a zero-initialized object.
-    const T& GetOrDefault(std::size_t index) const {
+    const T& GetOrDefault(std::size_t index) const noexcept {
+        if (base_ptr == nullptr || index >= size()) [[unlikely]] {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector RO access out of bounds @ {}", index);
+            return DefaultValue();
+        }
 #ifdef _WIN32
-        if (!IsCommittedPage(index)) {
-            return *reinterpret_cast<const T*>(&default_val);
+        if (!IsPageCommitted(static_cast<u64>(index) * sizeof(T))) {
+            return DefaultValue();
         }
 #endif
-        // On non-Windows, OS page table should optimize this by pointing to a zero page if unallocated.
         return base_ptr[index];
     }
 
     void Set(std::size_t index, const T& value) noexcept {
-        if (index > alloc_size / sizeof(T)) {
-            LOG_CRITICAL(Common_Memory, "Out of bounds write on SparseLargeVector @ {}", index);
+        if (base_ptr == nullptr || index >= size()) [[unlikely]] {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector write out of bounds @ {}", index);
+            return;
+        }
+        const u64 byte_offset = static_cast<u64>(index) * sizeof(T);
+        if (!CommitPage(byte_offset)) [[unlikely]] {
+            LOG_CRITICAL(Common_Memory, "SparseLargeVector commit failed for write @ {}", index);
             return;
         }
-        if (!IsCommittedPage(index))
-            CommitPage(index);
         base_ptr[index] = value;
     }
 
     void ZeroRegion(std::size_t start, std::size_t end_) noexcept {
-        u64 base = reinterpret_cast<u64>(&base_ptr[start]);
-        const u64 end = reinterpret_cast<u64>(&base_ptr[end_]);
+        if (base_ptr == nullptr || start >= end_) return;
 
-        const u64 end_page = AlignUp(base, HostPageSize);
-        const u64 first_size = (std::min)(end_page, end) - base;
+        const u64 start_off = static_cast<u64>(start) * sizeof(T);
+        const u64 end_off = static_cast<u64>(end_) * sizeof(T);
+        const u64 first_page_end = (start_off + HostPageSize - 1) & HostPageMask;
 
-        if (IsCommittedPage(start)) {
-            std::memset(reinterpret_cast<void*>(base), 0, first_size);
+        if (start_off < first_page_end) {
+            const u64 chunk_end = (std::min)(first_page_end, end_off);
+            const u64 chunk_size = chunk_end - start_off;
+            if (chunk_size != 0 && IsPageCommitted(start_off)) {
+                std::memset(reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(base_ptr) + start_off), 0, chunk_size);
+            }
+            if (end_off <= first_page_end) return;
         }
 
-        if (end <= end_page)
-            return;
-
-        base = end_page;
-
-        for (u64 page = base; page < end; page += HostPageSize) {
-            auto index = (page - reinterpret_cast<u64>(base_ptr)) / sizeof(T);
-            if (!IsCommittedPage(index)) {
-                continue;
-            }
-
-            if (end - page >= HostPageSize) {
-                DecommitPage(index);
+        for (u64 off = first_page_end; off < end_off; off += HostPageSize) {
+            if (!IsPageCommitted(off)) continue;
+            const u64 remaining = end_off - off;
+            if (remaining >= HostPageSize) {
+                DecommitPage(off);
             } else {
-                std::memset(reinterpret_cast<void*>(page), 0, end - page);
+                std::memset(reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(base_ptr) + off), 0, remaining);
             }
         }
     }
 
-    constexpr void CommitRegion(size_t index, size_t end_) {
-        const u64 base = static_cast<u64>(index) * sizeof(T);
-        const u64 end = static_cast<u64>(end_) * sizeof(T);
-
-        for (u64 page = AlignDown(base, HostPageSize); page < end; page += HostPageSize) {
-            if (!IsCommittedPage(page / sizeof(T))) {
-                CommitPage(page / sizeof(T));
+    void CommitRegion(std::size_t index, std::size_t end_) noexcept {
+        if (base_ptr == nullptr || index >= end_) return;
+        const u64 start_off = static_cast<u64>(index) * sizeof(T);
+        const u64 end_off = static_cast<u64>(end_) * sizeof(T);
+        const u64 start_page = start_off & HostPageMask;
+        for (u64 off = start_page; off < end_off; off += HostPageSize) {
+            if (!IsPageCommitted(off)) {
+                (void)CommitPage(off);
             }
         }
     }
 
-    constexpr T& GetUnchecked(size_t index) {
-        return base_ptr[index];
-    }
+    T& GetUnchecked(std::size_t index) noexcept { return base_ptr[index]; }
 
-    [[nodiscard]] constexpr const T& operator[](std::size_t index) const noexcept {
-        return GetOrDefault(index);
-    }
-
-    [[nodiscard]] constexpr const T* data() const noexcept {
-        return base_ptr;
-    }
-
-    [[nodiscard]] constexpr std::size_t size() const noexcept {
-        return alloc_size / sizeof(T);
-    }
+    [[nodiscard]] const T& operator[](std::size_t index) const noexcept { return GetOrDefault(index); }
+    [[nodiscard]] const T* data() const noexcept { return base_ptr; }
+    [[nodiscard]] std::size_t size() const noexcept { return alloc_size / sizeof(T); }
 
 private:
-    [[nodiscard]] constexpr bool IsCommittedPage(std::size_t index) const noexcept {
-        if (index > alloc_size / sizeof(T)) {
-            LOG_CRITICAL(Common_Memory, "Out of bounds access on large vector @ {}", index);
+    void Allocate(std::size_t new_size) noexcept {
+        alloc_size = new_size;
+        if (alloc_size == 0) {
+            base_ptr = nullptr;
+            committed_pages.reset();
+            return;
+        }
+        base_ptr = static_cast<T*>(AllocateMemoryPages(alloc_size));
+        const std::size_t num_pages = NumPages();
+        const std::size_t num_words = (num_pages + 63) / 64;
+        committed_pages = std::make_unique<std::atomic<u64>[]>(num_words);
+    }
+
+    void Release() noexcept {
+        if (base_ptr != nullptr) {
+            FreeMemoryPages(base_ptr, alloc_size);
+            base_ptr = nullptr;
+        }
+        committed_pages.reset();
+        alloc_size = 0;
+    }
+
+    [[nodiscard]] u64 NumPages() const noexcept {
+        return (alloc_size + HostPageSize - 1) >> HostPageBits;
+    }
+
+    [[nodiscard]] bool IsPageCommitted(u64 byte_offset) const noexcept {
+        const u64 page_index = byte_offset >> HostPageBits;
+        if (committed_pages == nullptr || page_index >= NumPages()) return false;
+        const auto val = committed_pages[page_index >> 6].load(std::memory_order_acquire);
+        return (val >> (page_index & 63)) & 1;
+    }
+
+    void SetPageBit(u64 page_index, bool value) noexcept {
+        if (committed_pages == nullptr) return;
+        const u64 bit = 1ULL << (page_index & 63);
+        auto& atom = committed_pages[page_index >> 6];
+        if (value) {
+            atom.fetch_or(bit, std::memory_order_release);
+        } else {
+            atom.fetch_and(~bit, std::memory_order_release);
+        }
+    }
+
+    bool CommitPage(u64 byte_offset) noexcept {
+        const u64 page_index = byte_offset >> HostPageBits;
+        const uintptr_t page_addr = (reinterpret_cast<uintptr_t>(base_ptr) + byte_offset) & HostPageMask;
+
+        if (IsPageCommitted(byte_offset)) return true;
+
+#if defined(_WIN32)
+        if (!CommitVectorPage(page_addr, true)) return false;
+#else
+        if (mprotect(reinterpret_cast<void*>(page_addr), HostPageSize, PROT_READ | PROT_WRITE) != 0) {
+            LOG_ERROR(Common_Memory, "mprotect failed at {:#x}: {}", page_addr, std::strerror(errno));
             return false;
         }
-
-        auto page = (index * sizeof(T)) >> HostPageBits;
-        auto val = committed_pages[page >> 6].load(std::memory_order_acquire);
-        return (val >> (page & 63)) & 1;
-    }
-
-    constexpr void CommitPage(std::size_t index) noexcept {
-        auto page_index = (index * sizeof(T)) >> HostPageBits;
-        auto page = reinterpret_cast<uintptr_t>(base_ptr + index) & HostPageMask;
-#if defined(_WIN32)
-        CommitVectorPage(page, true);
-#else
-        mprotect(reinterpret_cast<void*>(page), HostPageSize, PROT_READ | PROT_WRITE);
 #endif
-
-        committed_pages[page_index >> 6].fetch_or(1ULL << (page_index & 63), std::memory_order_release);
+        SetPageBit(page_index, true);
+        return true;
     }
 
-    constexpr void DecommitPage(std::size_t index) noexcept {
-        auto page_index = (index * sizeof(T)) >> HostPageBits;
-        auto page = reinterpret_cast<uintptr_t>(base_ptr + index) & HostPageMask;
+    void DecommitPage(u64 byte_offset) noexcept {
+        const u64 page_index = byte_offset >> HostPageBits;
+        const uintptr_t page_addr = (reinterpret_cast<uintptr_t>(base_ptr) + byte_offset) & HostPageMask;
+        DecommitVectorPage(page_addr);
+        SetPageBit(page_index, false);
+    }
 
-        committed_pages[page_index >> 6].fetch_and(~(1ULL << (page_index & 63)), std::memory_order_release);
-        DecommitVectorPage(page);
+    [[nodiscard]] const T& DefaultValue() const noexcept {
+        return *reinterpret_cast<const T*>(&default_val);
     }
 
     std::size_t alloc_size{};
     T* base_ptr{};
-
-    std::vector<std::atomic<u64>> committed_pages{};
-#ifdef _WIN32
-    const std::array<u8, sizeof(T)> default_val{};
-#endif
+    std::unique_ptr<std::atomic<u64>[]> committed_pages{};
+    alignas(T) const std::array<u8, sizeof(T)> default_val{};
 };
 
-} // namespace Common
+} // namespace Common