ZTS: optimize ksmtuned settings

[mcmilk]

Don't use KSM on the FreeBSD VMs and optimize ksmtuned settings for faster ZTS test runs.

Free kernel caches on Linux VMs via cron, to get more usable memory on them.

Motivation and Context

Some ZTS test runs fail because of memory pressure. This PR tries to fix this.

Description

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[tonyhutter]

Free kernel caches on Linux VMs via cron, to get more usable memory on them.

For Linux, you might be better off playing with some of the virtual memory tunables on either the runner or the VMs. For example, have you tried setting vm.min_free_kbytes to higher values?

[mcmilk]

Free kernel caches on Linux VMs via cron, to get more usable memory on them.

For Linux, you might be better off playing with some of the virtual memory tunables on either the runner or the VMs. For example, have you tried setting vm.min_free_kbytes to higher values?

Yes, I am trying to guess - which screw I should turn.... this is a first try.