When a paging-space low condition is detected, additional paging space should be defined. The system monitors the number of free paging space blocks and detects when a paging-space shortage exists. Processes that dynamically allocate memory can ensure that sufficient paging space exists by monitoring the paging-space levels with the psdanger subroutine or by using special allocation routines. You can use the disclaim subroutine to prevent processes from ending when the paging-space kill level is reached. The default late allocation algorithm for memory and paging space allocation assists in the efficient use of disk resources and supports applications of customers who wish to take advantage of a sparse allocation algorithm for resource management.
Some programs allocate large amounts of virtual memory and then use only a fraction of the memory.
Examples of such programs are technical applications that use sparse vectors or matrices as data structures. For AIX 4.3.2 and later, the late allocation algorithm is modified to further delay the allocation of paging space. As mentioned above, before AIX 4.3.2, paging space was allocated when a page was touched. However, this paging space may never be used, especially on systems with large real memory where paging is rare. Therefore, the allocation of paging space is delayed until it is necessary to page out the page, which results in no wasted paging space allocation.