The fork() retry interval parameter

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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 pacefork parameter of the schedo 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 might allow processes to delay long enough to be released like in the following example:

# schedo -o pacefork=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.