[Linux] Implement KSM Kernel Samepage Merging with Maps (#4601)

* KSM work

* Windows fixes

* Add KSM logging, cleanup

* Cleanup raycast logging

common/memory/ksm.hpp

@@ -0,0 +1,220 @@
+#ifndef EQEMU_KSM_HPP
+#define EQEMU_KSM_HPP
+
+#include "../eqemu_logsys.h"
+#include <iostream>
+#include <vector>
+#include <cstring>
+#ifdef _WIN32
+#include <malloc.h>  // For _aligned_malloc, _aligned_free
+#include <windows.h>
+#else
+#include <sys/mman.h>  // For madvise
+#include <unistd.h>    // For sysconf, sbrk
+#endif
+
+
+// Page-aligned allocator for std::vector
+template <typename T>
+class PageAlignedAllocator {
+public:
+	using value_type = T;
+
+	PageAlignedAllocator() noexcept = default;
+	template <typename U>
+	PageAlignedAllocator(const PageAlignedAllocator<U>&) noexcept {}
+
+	T* allocate(std::size_t n) {
+		void* ptr = nullptr;
+		size_t size = n * sizeof(T);
+
+#ifdef _WIN32
+		// Simply allocate memory without alignment
+        ptr = malloc(size);
+        if (!ptr) throw std::bad_alloc();
+#else
+		size_t alignment = getPageSize(); // Get the system's page size
+		if (posix_memalign(&ptr, alignment, size) != 0) {
+			throw std::bad_alloc();
+		}
+#endif
+		return static_cast<T*>(ptr);
+	}
+
+	void deallocate(T* p, std::size_t) noexcept {
+		free(p);
+	}
+
+private:
+	size_t getPageSize() const
+	{
+#ifdef _WIN32
+		SYSTEM_INFO sysInfo;
+		GetSystemInfo(&sysInfo);
+		return sysInfo.dwPageSize; // Page size in bytes
+#else
+		return static_cast<size_t>(sysconf(_SC_PAGESIZE));
+#endif
+	};
+};
+
+template <typename T, typename U>
+bool operator==(const PageAlignedAllocator<T>&, const PageAlignedAllocator<U>&) noexcept {
+	return true;
+}
+
+template <typename T, typename U>
+bool operator!=(const PageAlignedAllocator<T>&, const PageAlignedAllocator<U>&) noexcept {
+	return false;
+}
+
+// Kernel Samepage Merging (KSM) functionality
+namespace KSM {
+
+#ifdef _WIN32
+	// Windows-specific placeholder functions (no-op)
+    inline void CheckPageAlignment(void* ptr) {
+    }
+
+    inline void* AllocatePageAligned(size_t size) {
+        return memset(malloc(size), 0, size);
+    }
+
+    inline void MarkMemoryForKSM(void* start, size_t size) {
+    }
+
+    inline void AlignHeapToPageBoundary() {
+    }
+
+    inline void* MarkHeapStart() {
+        return nullptr;
+    }
+
+    inline size_t MeasureHeapUsage(void* start) {
+        return 0;
+    }
+#else
+	// Linux-specific functionality
+	inline void CheckPageAlignment(void* ptr) {
+		size_t page_size = sysconf(_SC_PAGESIZE);
+		if (reinterpret_cast<uintptr_t>(ptr) % page_size == 0) {
+			LogKSMDetail("Memory is page-aligned [{}]", ptr);
+		} else {
+			LogKSMDetail("Memory is NOT page-aligned [{}]", ptr);
+		}
+	}
+
+	inline void* AllocatePageAligned(size_t size) {
+		size_t page_size = sysconf(_SC_PAGESIZE);
+		void* aligned_ptr = nullptr;
+		if (posix_memalign(&aligned_ptr, page_size, size) != 0) {
+			LogKSM("Failed to allocate page-aligned memory on Linux. page_size [{}] size [{}] bytes", page_size, size);
+		}
+		std::memset(aligned_ptr, 0, size);
+		return aligned_ptr;
+	}
+
+	inline void MarkMemoryForKSM(void* start, size_t size) {
+		if (madvise(start, size, MADV_MERGEABLE) == 0) {
+			LogKSM("Marked memory for KSM | start [{}] size [{}] bytes", start, size);
+		} else {
+			perror("madvise failed");
+		}
+	}
+
+	inline void AlignHeapToPageBoundary() {
+		size_t page_size = sysconf(_SC_PAGESIZE);
+		if (page_size == 0) {
+			LogKSM("Failed to retrieve page size SC_PAGESIZE [{}]", page_size);
+			return;
+		}
+
+		void* current_break = sbrk(0);
+		if (current_break == (void*)-1) {
+			LogKSM("Failed to retrieve the current program break");
+			return;
+		}
+
+		uintptr_t current_address = reinterpret_cast<uintptr_t>(current_break);
+		size_t misalignment = current_address % page_size;
+
+		if (misalignment != 0) {
+			size_t adjustment = page_size - misalignment;
+			if (sbrk(adjustment) == (void*)-1) {
+				LogKSM("Failed to align heap to page boundary. adjustment [{}] bytes", adjustment);
+				return;
+			}
+		}
+
+		LogKSMDetail("Heap aligned to next page boundary. Current break [{}]", sbrk(0));
+	}
+
+	inline void* MarkHeapStart() {
+		void* current_pos = sbrk(0);
+		AlignHeapToPageBoundary();
+		return current_pos;
+	}
+
+	inline size_t MeasureHeapUsage(void* start) {
+		void* current_break = sbrk(0);
+		return static_cast<char*>(current_break) - static_cast<char*>(start);
+	}
+#endif
+
+
+	inline size_t getPageSize()
+	{
+#ifdef _WIN32
+		SYSTEM_INFO sysInfo;
+		GetSystemInfo(&sysInfo);
+		return sysInfo.dwPageSize; // Page size in bytes
+#else
+		return static_cast<size_t>(sysconf(_SC_PAGESIZE)); // POSIX page size
+#endif
+	};
+
+	template <typename T>
+	inline void PageAlignVectorAligned(std::vector<T, PageAlignedAllocator<T>>& vec) {
+		if (vec.empty()) {
+			return;
+		}
+
+		size_t page_size = getPageSize();
+		void* start = vec.data();
+		size_t size = vec.size() * sizeof(T);
+
+		// Check if the memory is page-aligned
+		if (reinterpret_cast<std::uintptr_t>(start) % page_size != 0) {
+			// Allocate a new aligned vector
+			std::vector<T, PageAlignedAllocator<T>> aligned_vec(vec.get_allocator());
+			aligned_vec.reserve(vec.capacity()); // Match capacity to avoid reallocation during copy
+
+			// Copy elements from the original vector
+			aligned_vec.insert(aligned_vec.end(), vec.begin(), vec.end());
+
+			// Swap the aligned vector with the original vector
+			vec.swap(aligned_vec);
+
+			// Clear the temporary aligned vector to free its memory
+			aligned_vec.clear();
+
+			// Verify the new alignment
+			start = vec.data();
+			if (reinterpret_cast<std::uintptr_t>(start) % page_size != 0) {
+				throw std::runtime_error("Failed to align vector memory to page boundaries.");
+			}
+
+			LogKSMDetail("Vector reallocated to ensure page alignment. start [{}] size [{}] bytes", start, size);
+		} else {
+			LogKSMDetail("Vector is already page-aligned. start [{}] size [{}] bytes", start, size);
+		}
+
+#ifndef _WIN32
+		// Mark memory for KSM (only on non-Windows systems)
+		MarkMemoryForKSM(start, size);
+#endif
+	}
+
+}
+
+#endif // EQEMU_KSM_HPP