PPT Slide
Virtual Memory System Examples
- Swap area: section of a disk reserved for pages.
- In emergencies, most UNIXes can swap to a file in the filesystem using the “mkfile” and “swapon” commands.
- Various optimizations can be done at process creation to minimize initial swap disk traffic (Figure 12.24).
- Copy-on-write: useful trick for implementing UNIX fork(). A child initially shares all the pages with it’s parent in a read-only fashion and the parent’s page table entries are all set to read-only When child or parent attempts to change a page a new copy of the page is created in a new page frame and the page table adjusted accordingly (Figure 12.25). This is more efficient than simply duplicating the parent’ memory.