Lecture 10 - Virtual memory #

Scope of the lecture #

Virtual memory - fundamentals:
- Motivation: smaller memory allocation ⇒ better utilization, higher degree of multi-programming, smaller I/O -related overhead; virtual address space can be much larger than physical and sparse
- Implementations: demand paging, demand segmentation
- Memory management unit (MMU)
Demand paging:
- valid-invalid bid, page fault, page swapping
- lazy swapping, pager
- memory reference locality and page fault frequency
- CPU instruction restart
- average performance of demand paging, average memory access time
- page/frame replacement algorithms: FIFO, OPT, LRU and approximations; Belady effect
- page buffering and raw disk mode
- allocation of frames to a process: equal/proportional/priority, local/global; NUMA, CPU affinityS.
- thrashing: causes, symptoms, remedies; working-set mode, page-fault frequency, middle-term scheduler.
Measures to improve the use of memory access:
- memory-mapped files; memory-mapped I/O devices
- copy-on-write(COW) and efficiency of fork()
- allocating kernel memory; buddy algorithm, slab algorithm
- locality of memory references and efficiency of large data structures processing
Examples of VM implementations: Windows, Unix, Linux