Jenkins server is running slow

If Java memory is causing the problem, then you can add more heap via the -Xmx option, as suggested in Priyam's answer. By default, JVM limits heap to 25% of your available RAM.

More heap has a caveat, though: if you add heap in the range of several GB, then the default JVM garbage collection algorithm will periodically impose stop-the-world breaks in the range of several seconds. You then need to switch to a custom garbage collection algorithm (like, CMS) and then carefully tune its parameters.

If adding more heap does not fix your problem, then you need to dig deeper. There's a plethora of possible root causes for a slow master -- from JVM memory and garbage collection settings to plugin issues, on top of the usual CPU/disk/IO-dimensioning issues.

You can allocate more memory and swap heap sizes using the following commands.

These can be set in the job configuration or Jenkins -> Manage -> Configure

-Xmx512m
-XX:MaxPermSize=128m