Advantages: logical address space can be larger than physical, can be shared by multiple processes, efficient process creation
On-demand paging: Advantages: can reduce I/O, reduce memory usage, and fast response time
Valid bit (physical memory) invalid bit (virtual memory) distinguishes whether it is in virtual memory
Page fault: Accessed page not in memory
Solution: Check whether the internal page table reference of the process is legal, if it is legal, it will be transferred into memory, and if it is not legal, the process will be terminated
The free buffer pool allocates free pages
Page Replacement: On-Demand Paging Basics, Separate Logical and Physical Memory
Thrashing: A process frequently page faults. As a result, the CPU usage rate drops, and the process grabs the frames of other processes
Operations on files on disk: direct operations, memory mapping
Kernel memory allocation: bluddy allocation (multiples of 2), slab allocation (one or more pages, cache has multiple slabs)
File concept: It is the smallest allocation unit of logical external storage, roughly divided into data and programs. Genuine types have different structures
Properties: name, identifier, type, location, size, protection, time
System open file table, process open file table
File pointers, open counters, disk locations, access permissions
Locking: shared lock/private lock, the operating system can force or suggest locking
Access method: sequential, direct, indexed
directory structure (volume: a large chunk of space where the file system is stored)
Single-layer, double-layer, tree-like (forbidden to share file directories), acyclic graph (implementation: symbolic link, non-symbolic link), general graph
File system installation: the operating system needs to know the device name, installation location
File sharing: via FTP\distributed file system, browser
Remote file system failure and local file system failure add new failure modes and record status information
