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// 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
inline const u64 HostPageSize = 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;
void FreeMemoryPages(void* base, std::size_t size) noexcept;
void DecommitVectorPage(uintptr_t base) noexcept;
/// A large page-aligned buffer that has optimized memory usage for zero-writes.
template <typename T>
// MSVC doesn't regard structs with atomics as trivially copyable
// 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)) {
UNREACHABLE_MSG("Cannot access SparseLargeVector index {} with RW permission", 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)) {
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) {
auto index = (page - reinterpret_cast<u64>(base_ptr)) / sizeof(T);
if (!IsCommittedPage(index)) {
continue;
}
if (end - page >= HostPageSize) {
DecommitPage(index);
} else {
std::memset(reinterpret_cast<void*>(page), 0, 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 bool 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)
if (!CommitVectorPage(page, true)) {
return false;
}
#else
if (mprotect(reinterpret_cast<void*>(page), HostPageSize, PROT_READ | PROT_WRITE) != 0) {
LOG_ERROR(Common_Memory, "Failed to commit large buffer region at index {}, error {}", index, strerror(errno));
return false;
}
#endif
committed_pages[page_index >> 6].fetch_or(1ULL << (page_index & 63), std::memory_order_release);
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;
committed_pages[page_index >> 6].fetch_and(~(1ULL << (page_index & 63)), std::memory_order_release);
DecommitVectorPage(page);
}
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
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