If available paging space depletes to a low level, the operating system attempts to release resources by first warning processes to release paging space and finally by killing processes if there still is not enough paging space available for the current processes.
The npswarn and npskill thresholds are used by the VMM to determine when to first warn processes and eventually when to kill processes.
These two parameters can be set through the vmtune command:
npswarn = maximum (512, 4*npskill)
The value of npswarn must be greater than zero and less than the total number of paging-space pages on the system. It can be changed with the command vmtune -w.
npskill = maximum (64, number_of_paging_space_pages/128)
The npskill value must be greater than zero and less than the total number of paging space pages on the system. It can be changed with the command vmtune -k.
By setting the nokilluid option to a nonzero value with the command vmtune -n, user IDs lower than this value will be exempt from being killed because of low page-space conditions. This option is only available in operating system version 22.214.171.124 and later.
If a process cannot be forked due to a lack of paging-space pages, the scheduler will retry the fork five times. In between each retry, the scheduler will delay for a default of 10 clock ticks.
The -f parameter of the schedtune command specifies the number of clock ticks to wait before retrying a failed fork() call. For example, if a fork() subroutine call fails because there is not enough space available to create a new process, the system retries the call after waiting the specified number of clock ticks. The default value is 10, and because there is one clock tick every 10 ms, the system would retry the fork() call every 100 ms.
If the paging space is low only due to brief, sporadic workload peaks, increasing the retry interval (such as in the following) might allow processes to delay long enough to be released:
# /usr/samples/kernel/schedtune -f 15
In this way, when the system retries the fork() call, there is a higher chance of success because some processes might have finished their execution and, consequently, released pages from paging space.