This paper is about AIX (IBM'S UNIX flavour)
AIX Memory Management
Understanding How AIX Manages Memory / Page Space.
Data is essentially held in pages of 4096B, and a page in RAM is accessible by the CPU, if the page is on disk the CPU can't access it directly.
A page fault occurs when a wanted page address does not translate to a real memory address. At this point the Virtual Memory Manager (VMM) knows it needs to get data from disk and place it in RAM - it therefore checks to see that there is space in RAM in which to out this data.
If there's enough room, VMM checks to see if the wanted page has been used previously by this process:
- if not, an "initial page fault", VMM allocates _two_ pages for the data; one in RAM and the other on a backing page on disk where it can go if it has to be temporarily removed from RAM. This is known as "late page space allocation".
- if it has, a "repage fault" I/O is scheduled to bring the data back from disk and into RAM -......
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