CSE 131 Lecture Notes - Lecture 15: Virtual Memory, Memory Address, Page Fault
Document Summary
Use slabs (each 1+ pages long) to allocate and manage a large number of equal-sized objects. Free a slab only when all of its objects are freed. Keep track of free objects and hand out again when needed. Process must fit into physical memory (impossible to run larger processes) External fragmentation: lots of small free areas. Compaction needed to reassemble larger free areas. Processes are either in memory or on disk. Bring in pieces of the process over time (typically data) Still doesn"t solve the problem of fragmentation or partially resident processes. Basic idea: allow os to hand out more memory than exists on the system. Keep recently used stuff in physical memory. Move less recently used stuff to disk. Keep all of this hidden from processes. Processes still see an address space from 0 to max_address. Movement of information to and from disk handled by the os without process help. Virtual memory (vm) especially helpful in multiprogrammed systems.
