[common/core/dynarmic] Optimize page table allocations (#4219)

Reduces the page entries from 32 bytes to 8 and rewrites `VirtualBuffer` to be more efficient in memory usage and specifically for large zero regions.

The page table will now only reserve 1GiB instead of 4GiB and of this memory it should only use at most ~8MiB.

This PR has the side effect of using Eden on Windows on low memory systems much more plausible since it would previously require ~10GiB of committable memory at front (despite using ~5-6 at most, inadvertently stalling other processes) where as now it should only require around the amount that it'll actually use.

Co-authored-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4219
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Reviewed-by: lizzie <lizzie@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

src/common/CMakeLists.txt

@@ -108,6 +108,8 @@ add_library(
     settings_setting.h
     slot_vector.h
     socket_types.h
+    sparse_large_vector.cpp
+    sparse_large_vector.h
     spin_lock.h
     stb.cpp
     stb.h
@@ -137,8 +139,6 @@ add_library(
     uuid.cpp
     uuid.h
     vector_math.h
-    virtual_buffer.cpp
-    virtual_buffer.h
     zstd_compression.cpp
     zstd_compression.h
     fs/ryujinx_compat.h fs/ryujinx_compat.cpp

src/common/fiber.cpp

@@ -9,7 +9,6 @@
 
 #include "common/assert.h"
 #include "common/fiber.h"
-#include "common/virtual_buffer.h"
 
 #include <boost/context/detail/fcontext.hpp>
 

src/common/host_memory.cpp

@@ -178,6 +178,14 @@ public:
         Release();
     }
 
+    void* Allocate(size_t size) {
+        auto* ptr = VirtualAlloc(nullptr, size, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+        if (ptr == nullptr) {
+            LOG_CRITICAL(HW_Memory, "Failed to allocate fallback buffer with size {:#x}, error {}", size, GetLastError());
+        }
+        return ptr;
+    }
+
     void Map(size_t virtual_offset, size_t host_offset, size_t length, MemoryPermission perms) {
         std::unique_lock lock{placeholder_mutex};
         if (!IsNiechePlaceholder(virtual_offset, length)) {
@@ -398,6 +406,10 @@ private:
 // For managarm: see https://github.com/managarm/managarm/issues/1370
 #else // ^^^ Windows ^^^ vvv POSIX vvv
 
+#ifndef MAP_NOCORE
+#define MAP_NOCORE 0
+#endif
+
 #ifdef ARCHITECTURE_arm64
 
 static void* ChooseVirtualBase(size_t virtual_size) {
@@ -422,7 +434,7 @@ static void* ChooseVirtualBase(size_t virtual_size) {
         // Note: we may be able to take advantage of MAP_FIXED_NOREPLACE here.
         void* map_pointer =
             mmap(reinterpret_cast<void*>(hint_address), virtual_size, PROT_READ | PROT_WRITE,
-                 MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
+                 MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE | MAP_NOCORE, -1, 0);
 
         // If we successfully mapped, we're done.
         if (reinterpret_cast<uintptr_t>(map_pointer) == hint_address) {
@@ -442,11 +454,11 @@ static void* ChooseVirtualBase(size_t virtual_size) {
 
 static void* ChooseVirtualBase(size_t virtual_size) {
 #if defined(__FreeBSD__) || defined(__DragonFly__) || defined(__OpenBSD__) || defined(__sun__) || defined(__HAIKU__) || defined(__managarm__) || defined(__AIX__)
-    void* virtual_base = mmap(nullptr, virtual_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE | MAP_ALIGNED_SUPER, -1, 0);
+    void* virtual_base = mmap(nullptr, virtual_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE | MAP_ALIGNED_SUPER | MAP_NOCORE, -1, 0);
     if (virtual_base != MAP_FAILED)
         return virtual_base;
 #endif
-    return mmap(nullptr, virtual_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
+    return mmap(nullptr, virtual_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE | MAP_NOCORE, -1, 0);
 }
 
 #endif
@@ -540,13 +552,13 @@ public:
         }
         if (use_anon) {
             LOG_WARNING(Common_Memory, "Using private mappings instead of shared ones");
-            backing_base = static_cast<u8*>(mmap(nullptr, backing_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0));
+            backing_base = static_cast<u8*>(mmap(nullptr, backing_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_NOCORE, -1, 0));
             if (fd > 0) {
                 fd = -1;
                 close(fd);
             }
         } else {
-            backing_base = static_cast<u8*>(mmap(nullptr, backing_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
+            backing_base = static_cast<u8*>(mmap(nullptr, backing_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_NOCORE, fd, 0));
         }
         if (backing_base == MAP_FAILED) {
             LOG_CRITICAL(HW_Memory, "mmap failed: {}", strerror(errno));
@@ -570,6 +582,14 @@ public:
         Release();
     }
 
+    void* Allocate(size_t size) {
+        auto* ptr = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+        if (ptr == MAP_FAILED) {
+            LOG_CRITICAL(HW_Memory, "Failed to allocate fallback buffer with size {:#x}, {}", size, strerror(errno));
+        }
+        return ptr;
+    }
+
     void Map(size_t virtual_offset, size_t host_offset, size_t length, MemoryPermission perms) {
         // Intersect the range with our address space.
         AdjustMap(&virtual_offset, &length);
@@ -690,12 +710,10 @@ HostMemory::HostMemory(size_t backing_size_, size_t virtual_size_)
 {
 #if defined(__OPENORBIS__) || defined(__managarm__)
     LOG_WARNING(HW_Memory, "Platform doesn't support fastmem");
-    fallback_buffer.emplace(backing_size);
-    backing_base = fallback_buffer->data();
+    backing_base = static_cast<u8*>(mmap(nullptr, backing_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
     virtual_base = nullptr;
 #else
     // Try to allocate a fastmem arena.
-    // The implementation will fail with std::bad_alloc on errors.
     impl = std::make_unique<HostMemory::Impl>(AlignUp(backing_size, PageAlignment), AlignUp(virtual_size, PageAlignment) + HugePageSize);
     if (impl->Init()) {
         backing_base = impl->backing_base;
@@ -706,16 +724,26 @@ HostMemory::HostMemory(size_t backing_size_, size_t virtual_size_)
             virtual_base_offset = virtual_base - impl->virtual_base;
         }
     } else {
-        impl.reset();
         LOG_WARNING(HW_Memory, "Platform can support fastmem, but can't create it");
-        fallback_buffer.emplace(backing_size);
-        backing_base = fallback_buffer->data();
+        fallback_buffer = true;
+        backing_base = static_cast<u8*>(impl->Allocate(backing_size));
         virtual_base = nullptr;
+        impl.reset();
     }
 #endif
 }
 
-HostMemory::~HostMemory() = default;
+HostMemory::~HostMemory() {
+#ifdef _WIN32
+    if (fallback_buffer) {
+        VirtualFree(backing_base, backing_size, MEM_RELEASE);
+    }
+#else
+    if (fallback_buffer) {
+        munmap(backing_base, backing_size);
+    }
+#endif
+}
 
 HostMemory::HostMemory(HostMemory&&) noexcept = default;
 

src/common/host_memory.h

@@ -10,7 +10,6 @@
 #include <optional>
 #include "common/common_funcs.h"
 #include "common/common_types.h"
-#include "common/virtual_buffer.h"
 
 namespace Common {
 
@@ -86,7 +85,7 @@ private:
     u8* virtual_base{};
     size_t virtual_base_offset{};
     // Windows requires it for kernels whom lack proper support for some functions!
-    std::optional<Common::VirtualBuffer<u8>> fallback_buffer;
+    bool fallback_buffer{false};
 };
 
 } // namespace Common

src/common/page_table.cpp

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: Copyright 2019 yuzu Emulator Project
@@ -13,39 +13,11 @@ PageTable::PageTable() = default;
 
 PageTable::~PageTable() noexcept = default;
 
-bool PageTable::BeginTraversal(TraversalEntry* out_entry, TraversalContext* out_context,
-                               Common::ProcessAddress address) const {
-    out_context->next_offset = GetInteger(address);
-    out_context->next_page = address / page_size;
-
-    return this->ContinueTraversal(out_entry, out_context);
-}
-
-bool PageTable::ContinueTraversal(TraversalEntry* out_entry, TraversalContext* context) const {
-    // Setup invalid defaults.
-    out_entry->phys_addr = 0;
-    out_entry->block_size = page_size;
-    // Validate that we can read the actual entry.
-    if (auto const page = context->next_page; page < entries.size()) {
-        // Validate that the entry is mapped.
-        if (auto const paddr = entries[page].addr; paddr != 0) {
-            // Populate the results.
-            out_entry->phys_addr = paddr + context->next_offset;
-            context->next_page += 1;
-            context->next_offset += page_size;
-            return true;
-        }
-    }
-    context->next_page += 1;
-    context->next_offset += page_size;
-    return false;
-}
-
-void PageTable::Resize(std::size_t address_space_width_in_bits, std::size_t page_size_in_bits) {
-    auto const num_page_table_entries = 1ULL << (address_space_width_in_bits - page_size_in_bits);
-    entries.resize(num_page_table_entries);
+void PageTable::Resize(std::size_t address_space_width_in_bits, std::size_t page_bits) {
+    auto const num_page_table_entries = 1ULL << (address_space_width_in_bits - page_bits);
+    entries.ResizeAndClear(num_page_table_entries);
     current_address_space_width_in_bits = address_space_width_in_bits;
-    page_size = 1ULL << page_size_in_bits;
+    current_page_bits = page_bits;
 }
 
 } // namespace Common

src/common/page_table.h

@@ -9,22 +9,22 @@
 #include <atomic>
 
 #include "common/common_types.h"
+#include "common/sparse_large_vector.h"
 #include "common/typed_address.h"
-#include "common/virtual_buffer.h"
 
 namespace Common {
 
 enum class PageType : u8 {
     /// Page is unmapped and should cause an access error.
-    Unmapped,
+    Unmapped = 0b00,
     /// Page is mapped to regular memory. This is the only type you can get pointers to.
-    Memory,
+    Memory = 0b01,
     /// Page is mapped to regular memory, but inaccessible from CPU fastmem and must use
     /// the callbacks.
-    DebugMemory,
+    DebugMemory = 0b10,
     /// Page is mapped to regular memory, but also needs to check for rasterizer cache flushing and
     /// invalidation
-    RasterizerCachedMemory,
+    RasterizerCachedMemory = 0b11,
 };
 
 /**
@@ -42,57 +42,86 @@ struct PageTable {
         u64 next_offset{};
     };
 
-    /// Number of bits reserved for attribute tagging.
-    /// This can be at most the guaranteed alignment of the pointers in the page table.
-    static constexpr int ATTRIBUTE_BITS = 2;
+    /// Masks out bits reserved for attribute tagging.
+    static constexpr u64 ATTRIBUTE_MASK = ((1ULL << 44) - 1) << 12;
+
+    /// Specifies sign bit for page table entries.
+    static constexpr u64 SIGN_BIT = 45 + 12; // 44 bits of data + page offset
 
     /**
-     * Pair of host pointer and page type attribute.
-     * This uses the lower bits of a given pointer to store the attribute tag.
+     * Atomic tuple of host pointer, page type, and block id.
+     * This uses the lower bits of a given pointer to store the attributes.
      * Writing and reading the pointer attribute pair is guaranteed to be atomic for the same method
      * call. In other words, they are guaranteed to be synchronized at all times.
      */
-    class PageInfo {
+    class PageEntryData {
     public:
+        struct Data {
+            Data(bool marked_, PageType type_, u16 block_, u64 page_)
+                : marked(static_cast<u64>(marked_)       & 0b1)
+                , type(static_cast<u64>(type_)           & ((1ULL << 2) - 1))
+                , block(static_cast<u64>(block_)         & ((1ULL << 9) - 1))
+                , page((page_ >> 12)                     & ((1ULL << 45) - 1))
+                , block2((static_cast<u64>(block_) >> 9) & ((1ULL << 7) - 1)) {}
+            u64 marked : 1;
+            u64 type   : 2;
+            u64 block  : 9;
+            u64 page   : 45; // 44 bits of actual data (64 - page offset (12) - reserved (8)) + a sign bit
+            u64 block2 : 7;
+        };
+
+        [[nodiscard]] Data Raw() const noexcept {
+            return std::bit_cast<Data>(data_raw.load(std::memory_order_relaxed));
+        }
+
         /// Returns the page pointer
-        [[nodiscard]] uintptr_t Pointer() const noexcept {
-            return ExtractPointer(raw.load(std::memory_order_relaxed));
+        [[nodiscard]] uintptr_t Pointer(bool ignored_marked = false) const noexcept {
+            return ExtractPointer(std::bit_cast<Data>(data_raw.load(std::memory_order_relaxed)), ignored_marked);
         }
 
         /// Returns the page type attribute
         [[nodiscard]] PageType Type() const noexcept {
-            return ExtractType(raw.load(std::memory_order_relaxed));
+            return static_cast<PageType>(std::bit_cast<Data>(data_raw.load(std::memory_order_relaxed)).type);
+        }
+
+        /// Returns the block identifier.
+        [[nodiscard]] u16 Block() const noexcept {
+            return ExtractBlock(std::bit_cast<Data>(data_raw.load(std::memory_order_relaxed)));
         }
 
         /// Returns the page pointer and attribute pair, extracted from the same atomic read
-        [[nodiscard]] std::pair<uintptr_t, PageType> PointerType() const noexcept {
-            const uintptr_t non_atomic_raw = raw.load(std::memory_order_relaxed);
-            return {ExtractPointer(non_atomic_raw), ExtractType(non_atomic_raw)};
+        [[nodiscard]] std::tuple<uintptr_t, PageType, u16> PointerTypeBlock(bool ignore_marked = false) const noexcept {
+            const auto non_atomic_raw = std::bit_cast<Data>(data_raw.load(std::memory_order_relaxed));
+            return {ExtractPointer(non_atomic_raw, ignore_marked), static_cast<PageType>(non_atomic_raw.type), ExtractBlock(non_atomic_raw)};
         }
 
-        /// Returns the raw representation of the page information.
-        /// Use ExtractPointer and ExtractType to unpack the value.
-        [[nodiscard]] uintptr_t Raw() const noexcept {
-            return raw.load(std::memory_order_relaxed);
+        /// Write page info atomically
+        constexpr void Store(bool marked, PageType type, u16 block, uintptr_t pointer) noexcept {
+            data_raw.store(std::bit_cast<u64>(Data{marked, type, block, pointer}));
         }
 
-        /// Write a page pointer and type pair atomically
-        void Store(uintptr_t pointer, PageType type) noexcept {
-            raw.store(pointer | uintptr_t(type));
+        constexpr void MarkRasterizerCached() noexcept {
+            data_raw.fetch_or(0b111);
+        }
+
+        constexpr void MarkDebug(u64 ptr, u16 block) noexcept {
+            Store(true, PageType::DebugMemory, block, ptr);
         }
 
         /// Unpack a pointer from a page info raw representation
-        [[nodiscard]] static uintptr_t ExtractPointer(uintptr_t raw) noexcept {
-            return raw & (~uintptr_t{0} << ATTRIBUTE_BITS);
+        [[nodiscard]] static uintptr_t ExtractPointer(Data raw, bool ignore_marked = false) noexcept {
+            return raw.marked && !ignore_marked ? 0
+                // shift raw.page's fake sign bit to the actual sign bit, then sign extend
+                : ((s64)(raw.page << (64 - 44))) >> (64 - 44 - 12);
         }
 
-        /// Unpack a page type from a page info raw representation
-        [[nodiscard]] static PageType ExtractType(uintptr_t raw) noexcept {
-            return static_cast<PageType>(raw & ((uintptr_t{1} << ATTRIBUTE_BITS) - 1));
+        [[nodiscard]] static u16 ExtractBlock(Data raw) noexcept {
+            return static_cast<u16>(raw.block | (raw.block2 << 9));
         }
 
     private:
-        std::atomic<uintptr_t> raw;
+        std::atomic<u64> data_raw;
+        static_assert(sizeof(Data) == sizeof(std::atomic<u64>));
     };
 
     PageTable();
@@ -100,13 +129,8 @@ struct PageTable {
 
     PageTable(const PageTable&) = delete;
     PageTable& operator=(const PageTable&) = delete;
-
-    PageTable(PageTable&&) noexcept = default;
-    PageTable& operator=(PageTable&&) noexcept = default;
-
-    bool BeginTraversal(TraversalEntry* out_entry, TraversalContext* out_context,
-                        Common::ProcessAddress address) const;
-    bool ContinueTraversal(TraversalEntry* out_entry, TraversalContext* context) const;
+    PageTable(PageTable&&) noexcept = delete;
+    PageTable& operator=(PageTable&&) noexcept = delete;
 
     /**
      * Resizes the page table to be able to accommodate enough pages within
@@ -121,30 +145,14 @@ struct PageTable {
         return current_address_space_width_in_bits;
     }
 
-    bool GetPhysicalAddress(Common::PhysicalAddress* out_phys_addr,
-                            Common::ProcessAddress virt_addr) const {
-        if (virt_addr > (1ULL << this->GetAddressSpaceBits())) {
-            return false;
-        }
-
-        *out_phys_addr = entries[virt_addr / page_size].addr + GetInteger(virt_addr);
-        return true;
-    }
-
     /// Vector of memory pointers backing each page. An entry can only be non-null if the
     /// corresponding attribute element is of type `Memory`.
-    struct PageEntryData {
-        PageInfo ptr;
-        u64 block;
-        u64 addr;
-        u64 padding;
-    };
-    VirtualBuffer<PageEntryData> entries;
-    static_assert(sizeof(PageEntryData) == 32);
+    SparseLargeVector<PageEntryData> entries;
+    static_assert(sizeof(PageEntryData) == 8);
 
     u8* fastmem_arena{};
     std::size_t current_address_space_width_in_bits{};
-    std::size_t page_size{};
+    std::size_t current_page_bits{};
 };
 
 } // namespace Common

src/common/sparse_large_vector.cpp

@@ -0,0 +1,143 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+/* virtual_buffer.cpp */
+// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifdef _WIN32
+#include <windows.h>
+#include <mutex>
+#else
+#include <sys/mman.h>
+#endif
+
+#include "common/alignment.h"
+#include "common/assert.h"
+#include "common/sparse_large_vector.h"
+
+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
+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
+        return EXCEPTION_CONTINUE_SEARCH;
+    }
+
+    u64 addr = 0, addr2 = 0;
+
+    for (auto region: vector_regions) {
+        auto addr_shifted = exception_addr >> HostPageBits;
+        if (region.first <= addr_shifted && addr_shifted <= region.second) {
+            addr = addr_shifted;
+        }
+
+        // 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;
+        }
+    }
+
+    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);
+
+    // Commit this region
+    if (addr != 0) {
+        if (!CommitVectorPage(addr << HostPageBits, false)) {
+            return EXCEPTION_CONTINUE_SEARCH;
+        }
+    }
+    // Commit next region if needed
+    if (addr2 != 0) {
+        if (!CommitVectorPage(addr2 << HostPageBits, false)) {
+            return EXCEPTION_CONTINUE_SEARCH;
+        }
+    }
+
+    return EXCEPTION_CONTINUE_EXECUTION;
+}
+
+bool CommitVectorPage(uintptr_t addr, bool write) noexcept {
+    MEMORY_BASIC_INFORMATION info {};
+    auto res = VirtualQuery(reinterpret_cast<void*>(addr), &info, sizeof(info));
+    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_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);
+        return false;
+    }
+
+    auto perm = write ? PAGE_READWRITE : PAGE_READONLY;
+    void* res2 = VirtualAlloc(reinterpret_cast<LPVOID>(addr), HostPageSize, MEM_COMMIT, perm);
+    if (res2 == nullptr) {
+        LOG_ERROR(HW_Memory, "Failed to commit large buffer region at {:#x}, error {}", addr, GetLastError());
+        return false;
+    }
+
+    return true;
+}
+#endif
+
+#ifndef MAP_NOCORE
+#define MAP_NOCORE 0
+#endif
+
+void* AllocateMemoryPages(std::size_t size) noexcept {
+    if (auto page = HostPageSize; size % page != 0) {
+        LOG_WARNING(HW_Memory, "Allocating unaligned large vector with size {:#x}; aligning to {} page size", size, page);
+        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);
+
+        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));
+#endif
+    return base;
+}
+
+void FreeMemoryPages(void* base, [[maybe_unused]] std::size_t size) noexcept {
+    if (auto page = HostPageSize; size % page != 0) {
+        size = AlignUp(size, page);
+    }
+    if (!base)
+        return;
+#ifdef _WIN32
+    ASSERT(VirtualFree(base, 0, MEM_RELEASE));
+#else
+    ASSERT(munmap(base, size) == 0);
+#endif
+}
+
+} // namespace Common

src/common/sparse_large_vector.h

@@ -0,0 +1,194 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+/* virtual_buffer.h */
+// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <atomic>
+#include <bit>
+#include <utility>
+#include <vector>
+
+#ifndef _WIN32
+#include <unistd.h>
+#include <sys/mman.h>
+#endif
+
+#include "common/alignment.h"
+#include "common/assert.h"
+
+namespace Common {
+
+#ifdef _WIN32
+constexpr u64 HostPageSize = 0x1000;
+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);
+#endif
+
+void* AllocateMemoryPages(std::size_t size) noexcept;
+void FreeMemoryPages(void* base, std::size_t size) noexcept;
+
+/// A large page-aligned buffer that has optimized memory usage for zero-writes.
+template <typename T>
+requires std::is_trivially_copyable_v<T>
+class SparseLargeVector final {
+public:
+    constexpr 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);
+    }
+
+    ~SparseLargeVector() noexcept {
+        FreeMemoryPages(base_ptr, alloc_size);
+    }
+
+    SparseLargeVector(const SparseLargeVector&) = delete;
+    SparseLargeVector& operator=(const SparseLargeVector&) = delete;
+    SparseLargeVector(SparseLargeVector&& other) = delete;
+    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);
+        }
+    }
+
+    /// 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 (!IsCommittedPage(index)) {
+            CommitPage(index);
+        }
+        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 {
+#ifdef _WIN32
+        if (!IsCommittedPage(index)) {
+            return *reinterpret_cast<const T*>(&default_val);
+        }
+#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);
+            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_]);
+
+        const u64 end_page = AlignUp(base, HostPageSize);
+        const u64 first_size = (std::min)(end_page, end) - base;
+
+        if (IsCommittedPage(start / sizeof(T))) {
+            std::memset(reinterpret_cast<void*>(base), 0, first_size);
+        }
+
+        if (end <= end_page)
+            return;
+
+        base = end_page;
+
+        for (u64 page = base; page < end; page += HostPageSize) {
+            if (!IsCommittedPage((page - reinterpret_cast<u64>(base_ptr)) / sizeof(T))) {
+                continue;
+            }
+
+            std::memset(reinterpret_cast<void*>(page), 0, (std::min)( HostPageSize, end - page));
+        }
+    }
+
+    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));
+            }
+        }
+    }
+
+    constexpr T& GetUnchecked(size_t index) {
+        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);
+    }
+
+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);
+            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);
+    }
+
+    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
+};
+
+} // namespace Common

src/common/virtual_buffer.cpp

@@ -1,44 +0,0 @@
-// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
-// SPDX-License-Identifier: GPL-3.0-or-later
-
-// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
-// SPDX-License-Identifier: GPL-2.0-or-later
-
-#ifdef _WIN32
-#include <windows.h>
-#else
-#include <sys/mman.h>
-#endif
-
-#include "common/assert.h"
-#include "common/virtual_buffer.h"
-
-namespace Common {
-
-void* AllocateMemoryPages(std::size_t size) noexcept {
-#ifdef _WIN32
-    void* base = VirtualAlloc(nullptr, size, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
-    if (base == nullptr) {
-        // Probably failing to reserve is less likely than failing to commit
-        base = VirtualAlloc(nullptr, size, MEM_COMMIT, PAGE_READWRITE);
-    }
-#else
-    void* base = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
-    if (base == MAP_FAILED)
-        base = nullptr;
-#endif
-    ASSERT(base);
-    return base;
-}
-
-void FreeMemoryPages(void* base, [[maybe_unused]] std::size_t size) noexcept {
-    if (!base)
-        return;
-#ifdef _WIN32
-    ASSERT(VirtualFree(base, 0, MEM_RELEASE));
-#else
-    ASSERT(munmap(base, size) == 0);
-#endif
-}
-
-} // namespace Common

src/common/virtual_buffer.h

@@ -1,84 +0,0 @@
-// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
-// SPDX-License-Identifier: GPL-3.0-or-later
-
-// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
-// SPDX-License-Identifier: GPL-2.0-or-later
-
-#pragma once
-
-#include <utility>
-
-namespace Common {
-
-void* AllocateMemoryPages(std::size_t size) noexcept;
-void FreeMemoryPages(void* base, std::size_t size) noexcept;
-
-template <typename T>
-class VirtualBuffer final {
-public:
-    // TODO: Uncomment this and change Common::PageTable::PageInfo to be trivially constructible
-    // using std::atomic_ref once libc++ has support for it
-    // static_assert(
-    //     std::is_trivially_constructible_v<T>,
-    //     "T must be trivially constructible, as non-trivial constructors will not be executed "
-    //     "with the current allocator");
-
-    constexpr VirtualBuffer() = default;
-    explicit VirtualBuffer(std::size_t count) noexcept
-        : alloc_size{count * sizeof(T)}
-    {
-        base_ptr = reinterpret_cast<T*>(AllocateMemoryPages(alloc_size));
-    }
-
-    ~VirtualBuffer() noexcept {
-        FreeMemoryPages(base_ptr, alloc_size);
-    }
-
-    VirtualBuffer(const VirtualBuffer&) = delete;
-    VirtualBuffer& operator=(const VirtualBuffer&) = delete;
-
-    VirtualBuffer(VirtualBuffer&& other) noexcept
-        : alloc_size{std::exchange(other.alloc_size, 0)}
-        , base_ptr{std::exchange(other.base_ptr, nullptr)}
-    {}
-
-    VirtualBuffer& operator=(VirtualBuffer&& other) noexcept {
-        alloc_size = std::exchange(other.alloc_size, 0);
-        base_ptr = std::exchange(other.base_ptr, nullptr);
-        return *this;
-    }
-
-    void resize(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 = reinterpret_cast<T*>(AllocateMemoryPages(alloc_size));
-        }
-    }
-
-    [[nodiscard]] constexpr const T& operator[](std::size_t index) const noexcept {
-        return base_ptr[index];
-    }
-
-    [[nodiscard]] constexpr T& operator[](std::size_t index) noexcept {
-        return base_ptr[index];
-    }
-
-    [[nodiscard]] constexpr T* data() noexcept {
-        return base_ptr;
-    }
-
-    [[nodiscard]] constexpr const T* data() const noexcept {
-        return base_ptr;
-    }
-
-    [[nodiscard]] constexpr std::size_t size() const noexcept {
-        return alloc_size / sizeof(T);
-    }
-
-private:
-    std::size_t alloc_size{};
-    T* base_ptr{};
-};
-
-} // namespace Common