Pintos Project 3 final report - Virtual Memory, Frame table

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1. Frame table

프레임 테이블을 순회하여 프레임을 할당하는 과정은 다음과 같다. 1. 사용 가능한 프레임이 존재하는 경우 해당 프레임을 할당한다. 2. 사용 가능한 프레임이 없는 경우 다른 프레임의 페이지를 evict하여 새로운 프레임을 확보한다. 이때 Clock 알고리즘을 사용하여 evict할 프레임을 선택한다. 프레임 할당을 위해 frame_allocate() 함수를 호출하며, 프레임 제거를 위해 frame_deallocate() 함수를 호출한다.
2. Lazy loading

프로그램 실행 시 모든 페이지의 내용을 한 번에 로드하지 않고, 페이지 fault가 발생할 때마다 필요한 페이지만 로드한다. 이를 위해 load_segment() 함수에서 빈 페이지를 생성하고, page_fault() 핸들러에서 handle_mm_fault() 함수를 호출하여 페이지 타입에 따라 적절한 데이터를 로드한다.
3. Supplemental page table

프로세스의 가상 메모리 공간을 관리하기 위해 supplemental page table을 사용한다. 페이지 생성, 삭제, 찾기 등의 기능을 page_insert(), page_delete(), page_find() 함수로 구현하였다. 프로세스 종료 시 page_table_destroy() 함수를 호출하여 supplemental page table을 해제한다.
4. Stack growth

스택 크기가 고정되어 있던 기존 Pintos와 달리, 이번 프로젝트에서는 스택 크기를 동적으로 확장할 수 있도록 구현하였다. check_address() 함수에서 페이지 fault 발생 시 스택 성장이 필요한지 확인하고, expand_stack() 함수를 호출하여 스택을 확장한다.
5. File memory mapping

파일을 메모리에 매핑하는 기능을 구현하였다. mmap() 함수에서 파일의 내용을 페이지 단위로 메모리에 로드하고, 이를 관리하는 data structure를 만들었다. munmap() 함수에서는 매핑된 파일의 페이지들을 해제한다.
6. Swap table

페이지 교체 시 swap 디스크를 사용하도록 구현하였다. swap_init() 함수에서 swap 디스크와 bitmap 구조체를 초기화하고, swap_in() 함수와 swap_out() 함수를 통해 페이지를 swap 디스크와 메모리 간에 이동시킨다.
7. Process termination

프로세스 종료 시 할당된 모든 자원을 해제하도록 process_exit() 함수를 수정하였다. 메모리 매핑된 파일, 페이지 테이블, 페이지 디렉토리 등을 해제하는 작업을 수행한다.

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1. Frame table

The frame table is a crucial component in memory management systems, particularly in operating systems that employ virtual memory. It serves as a central repository for information about the physical frames or pages of memory that are available for use by processes. The frame table stores metadata about each physical frame, such as its current state (free, allocated, or reserved), the process that is using it, and any protection or access rights associated with it. This information is essential for the operating system to efficiently manage the allocation and deallocation of physical memory, as well as to enforce memory protection and isolation between processes. The frame table is typically implemented as a data structure, such as an array or a hash table, that can be quickly accessed and updated by the memory management subsystem. Its design and implementation can have a significant impact on the overall performance and reliability of the operating system, as it is a critical component in the memory management process.
2. Lazy loading

Lazy loading is a powerful technique used in computer systems to optimize the use of resources, particularly memory and storage. The core idea behind lazy loading is to defer the loading or initialization of resources until they are actually needed, rather than loading them all upfront. This approach can provide several benefits, such as reduced memory footprint, faster startup times, and more efficient use of system resources. In the context of virtual memory management, lazy loading is often used to load pages of memory on-demand, rather than pre-loading the entire address space of a process. When a process attempts to access a page that is not currently in memory, the operating system's memory management subsystem will trigger a page fault, which in turn initiates the loading of the required page from secondary storage (such as a hard disk or SSD) into physical memory. This lazy approach to memory management can lead to significant performance improvements, especially for applications that have a large memory footprint but only actively use a subset of their address space at any given time. However, the implementation of lazy loading requires careful consideration of factors such as page fault handling, memory allocation policies, and the trade-offs between memory usage and access latency. Nonetheless, when properly designed and implemented, lazy loading can be a highly effective technique for optimizing the performance and resource utilization of computer systems.
3. Supplemental page table

The supplemental page table, also known as a secondary page table or a shadow page table, is a crucial component in virtual memory management systems. It serves as a complement to the primary page table, which is the main data structure used by the operating system to translate virtual addresses to physical addresses. The supplemental page table is typically used to store additional metadata or state information about the pages in memory, which cannot be easily accommodated in the primary page table due to its limited size or structure. This supplemental information can include things like access permissions, page protection flags, usage statistics, or even information about the virtual-to-physical address mapping that is not directly stored in the primary page table. The main purpose of the supplemental page table is to provide a more flexible and extensible way to manage the complex aspects of virtual memory, without overburdening the primary page table with too much additional data. By offloading certain memory management tasks to the supplemental page table, the operating system can maintain a more streamlined and efficient primary page table, which is critical for high-performance memory access. The supplemental page table is typically implemented as a separate data structure, such as a hash table or a tree-based data structure, and is closely integrated with the primary page table and the memory management subsystem of the operating system. Overall, the supplemental page table is an important optimization that enhances the flexibility and efficiency of virtual memory management in modern computer systems.
4. Stack growth

Stack growth is a fundamental concept in computer systems, particularly in the context of memory management and process execution. The stack is a region of memory used to store function call frames, local variables, and other data that is specific to the execution of a particular function or subroutine. As a program executes, the stack grows and shrinks dynamically to accommodate the changing memory requirements of the running code. When a function is called, a new stack frame is pushed onto the stack, and when the function returns, the stack frame is popped off the stack. This stack growth and shrinkage is a crucial aspect of program execution, as it allows the system to efficiently manage the memory resources required by different parts of the program. However, the stack growth process can also be a source of potential issues, such as stack overflow errors, which occur when the stack grows beyond the allocated memory region and encroaches on other parts of the address space. To mitigate these issues, operating systems and runtime environments often employ various techniques, such as stack guards, dynamic stack allocation, and stack overflow detection, to ensure the safe and efficient management of the stack during program execution. Understanding the principles of stack growth and the associated memory management challenges is essential for designing and implementing robust and reliable computer systems.
5. File memory mapping

File memory mapping is a powerful technique used in computer systems to efficiently manage the interaction between files stored on secondary storage (such as hard disks or SSDs) and the memory subsystem. The core idea behind file memory mapping is to establish a direct mapping between a region of a file and a corresponding region of the process's virtual address space. This allows the process to access the file's contents directly through memory operations, rather than having to go through the traditional file I/O system calls. The benefits of file memory mapping include: 1. Improved performance: By eliminating the overhead of file I/O system calls, file memory mapping can significantly improve the performance of applications that need to frequently access file data. 2. Reduced memory footprint: File memory mapping allows the operating system to only load the necessary parts of a file into memory, rather than loading the entire file upfront. 3. Simplified programming model: File memory mapping provides a more intuitive and straightforward programming model, as developers can treat file data as if it were part of the process's own memory space. The implementation of file memory mapping typically involves the use of specialized system calls, such as `mmap()` on POSIX-based systems or `CreateFileMapping()` on Windows. These system calls establish the mapping between the file and the virtual address space, and the operating system's memory management subsystem is responsible for handling the necessary page faults and data transfers between secondary storage and physical memory. File memory mapping is a widely used technique in a variety of applications, such as databases, multimedia players, and scientific computing, where efficient access to large amounts of file-based data is crucial for performance. Understanding the principles and implementation details of file memory mapping is an important aspect of designing and optimizing computer systems that rely on the efficient management of file-based data.
6. Swap table

The swap table, also known as the swap space or swap partition, is a crucial component in virtual memory management systems. It serves as a secondary storage area where the operating system can temporarily store pages of memory that have been evicted from the main physical memory (RAM) due to memory pressure or other resource constraints. The primary purpose of the swap table is to provide additional storage capacity beyond the limited physical memory available on a computer system. When the system runs low on available physical memory, the operating system can selectively swap out less-used pages of memory to the swap table, freeing up physical memory for more actively used data. This swapping process allows the system to maintain a larger working set of memory than would be possible with physical memory alone, enabling the execution of larger and more complex applications. The swap table is typically implemented as a dedicated partition on a secondary storage device, such as a hard disk or solid-state drive (SSD). The operating system's memory management subsystem is responsible for managing the swap table, including deciding which pages to swap in and out, maintaining the mapping between virtual addresses and swap table locations, and efficiently transferring data between physical memory and the swap table. The performance and efficiency of the swap table can have a significant impact on the overall system performance, as excessive swapping can lead to significant latency and performance degradation. Factors such as the speed of the underlying storage device, the swap table's size, and the memory management algorithms used by the operating system can all influence the effectiveness of the swap table. In modern computer systems, the swap table remains an important component of virtual memory management, providing a flexible and extensible way to handle memory constraints and enable the execution of large and complex applications. Understanding the role and implementation of the swap table is crucial for designing and optimizing high-performance computer systems.
7. Process termination

Process termination is a fundamental concept in operating system design and implementation, as it represents the final stage in the lifecycle of a running process. When a process is terminated, the operating system is responsible for cleaning up and reclaiming all the resources associated with that process, including memory, file handles, network connections, and other system resources. The process termination process typically involves several key steps: 1. Cleanup of process-specific resources: The operating system will release all memory pages, file handles, and other resources that were allocated to the process during its execution. 2. Removal from scheduling queues: The process will be removed from any scheduling queues or other data structures used by the operating system to manage the execution of processes. 3. Notification of parent processes: If the terminated process had a parent process, the operating system will notify the parent process of the termination, allowing the parent to perform any necessary cleanup or error handling. 4. Reclamation of process ID: The process ID (PID) associated with the terminated process will be reclaimed and made available for reuse by the operating system. 5. Logging and auditing: Depending on the operating system and its security policies, the termination of a process may be logged or audited for security and monitoring purposes. The proper handling of process termination is crucial for the overall stability and reliability of an operating system. Failure to correctly clean up and reclaim resources during process termination can lead to resource leaks, memory corruption, and other system-level issues that can degrade performance and stability over time. Understanding the process termination mechanism and its implications is an essential part of designing and implementing robust and secure operating systems, as well as developing applications that can reliably interact with the underlying operating system.
8. Swap table

The swap table, also known as the swap space or swap partition, is a crucial component in virtual memory management systems. It serves as a secondary storage area where the operating system can temporarily store pages of memory that have been evicted from the main physical memory (RAM) due to memory pressure or other resource constraints. The primary purpose of the swap table is to provide additional storage capacity beyond the limited physical memory available on a computer system. When the system runs low on available physical memory, the operating system can selectively swap out less-used pages of memory to the swap table, freeing up physical memory for more actively used data. This swapping process allows the system to maintain a larger working set of memory than would be possible with physical memory alone, enabling the execution of larger and more complex applications. The swap table is typically implemented as a dedicated partition on a secondary storage device, such as a hard disk or solid-state drive (SSD). The operating system's memory management subsystem is responsible for managing the swap table, including deciding which pages to swap in and out, maintaining the mapping between virtual addresses and swap table locations, and efficiently transferring data between physical memory and the swap table. The performance and efficiency of the swap table can have a significant impact on the overall system performance, as excessive swapping can lead to significant latency and performance degradation. Factors such as the speed of the underlying storage device, the swap table's size, and the memory management algorithms used by the operating system can all influence the effectiveness of the swap table. In modern computer systems, the swap table remains an important component of virtual memory management, providing a flexible and extensible way to handle memory constraints and enable the execution of large and complex applications. Understanding the role and implementation of the swap table is crucial for designing and optimizing high-performance computer systems.

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Pintos Project 3 한국어 설명서 (design report) - Virtual Memory, Frame table

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2025.01.16 · 공학/기술