An overly high value for the nofile ulimit or the fs.file-max kernel tunable can cause slowness

Environment

• Red Hat Enterprise Linux 6, 7, or 8

Issue

• I set the nofile ulimit to unlimited and now my system is running slowly.
• System is slow after increasing the open files to a high value.

Resolution

Use trial-and-error to find a value for nofile (ulimit -n) or fs.file-max that is sufficient but not excessive. Techniques such as running lsof | wc -l or iterating through /proc/self/fd can be used to get the current number of open file descriptors, which can be used as a basis for tuning the limits.

Root Cause

Under investigation.

Diagnostic Steps

1. Observe system slowness when a high value is in place for ulimit -n or the fs.file-max tunable.
2. Reduce the relevant limit and see if the slowness improves.

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