mmap()
The mmap() callable service is typically used by a single process to map a file into
virtual memory by using the same sort of logic that is used by data-in-virtual (DIV). Each page of
the file requires three RSM control blocks (anchor block, user page, and kernel data space page).
Each additional user that is sharing a mmap page of a file will consume an additional control
block.
The __MAP_MEGA option of mmap() enables applications to map very large files without the system overhead in ESQA. If you have applications that use the __MAP_MEGA option, you do not need to be concerned with the preceding calculations. If you are not using _MAP_MEGA and issue mmap(), you can estimate the ESQA usage just as you would for shared memory.
The mmap() callable service returns an out-of-memory condition when it can no longer obtain shared storage without exceeding its respective shared storage limit.