Add sysctl_mem option for FreeBSD

[xbeaudouin]

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General information

This rework from Brad works on PR#578 and new PR from #696, with Allan suggestions.

Proposed changes

Making a sysctl_mem option per default.
This permit to have information using sysctl information in addition of other way to have this.
Since sysctl is always present on FreeBSD this information is alway given.

We should have a new section giving the following informations:

<<<sysctl_mem>>>
mem.cache 0
mem.free 188102864896
mem.total 274779779072
mem.used 79134859264
swap.free 8589934592
swap.total 8589934592
swap.used 0

Kind regards

[xbeaudouin]

Hello, any news about this PR ? Thanks

[xbeaudouin]

Dear check_mk maintainers, is there any news about this PR ?
Kind regards

[xbeaudouin]

@mo-ki Hello, any news about this PR? We discussed a lot on this previously...
Kind regards

[mo-ki]

Hi, sorry about the silence. I was on vacation. I haven't forgotten about this, but we're currently struggling with limited resources....

[mo-ki]

But I think my comments from #578 still remain valid.

[xbeaudouin]

Well sorry about pinged you on holidays, I hope the holidays was nice !
Well this PR is #696, that took your comments from #578 in consideration.

Really I hope this can be merged if possible. In the meantime I will add this PR on FreeBSD ports.

[mo-ki]

Oh, I see. In this case:

• The section in the agent should be enclosed in a function (that should be the case for all sections, but we're not there yet...)
• A parse function needs to be implemented in https:/Checkmk/checkmk/blob/master/cmk/plugins/collection/agent_based/mem_used_sections.py
• Interpretation and computations should be left to the parse function. The section can simply output all the required values: sysctl vm.stats.vm.v_page_size vm.stats... 2>&1.

[xbeaudouin]

Oh, I see. In this case:

* The section in the agent should be enclosed in a function (that should be the case for all sections, but we're not there yet...)

* A parse function needs to be implemented in `https:/Checkmk/checkmk/blob/master/cmk/plugins/collection/agent_based/mem_used_sections.py`

* Interpretation and computations should be left to the parse function. The section can simply output all the required values:  `sysctl vm.stats.vm.v_page_size vm.stats... 2>&1`.

This has been done.