Add descriptions for sysctls in kern_mib.c which lack them.

[rpokala]

Summary

r343532 noted the difference between "hw.realmem" and "hw.physmem", which I
was previously unaware of. I discovered that neither sysctl had a description
visible via sysctl -d, so I found where they were defined and added
suitable descriptions. While in the file, I went ahead and added descriptions
for all the others which lacked them.

[trond.endrestol_ximalas.info]

This is a step in the right direction. I appreciate the units are mentioned explicitly.

[kib]

sys/kern/kern_mib.c

192

modules, not drivers.

That said, also the dcons buffer, if any, is not accounted for, on x86.

205–206

Realmem is in fact silly and often not reliable.

It is the amount of memory reported by bios. which is often does not have any resemblance to the reality. If system somehow detects this, it reports the max memory address as the hw.realmem.

222

Again, this is not true. It is the difference between physmem (see above) and the size of wired memory. Many of kernel allocations do not wire underlying pages. Some user allocations are wired.

[rpokala]

Update descriptions based on Kostik's feedback.

[rpokala]

Thanks for the feedback, @kib; take another look?

[kib]

I do not like it. The sysctl descriptions are supposed to be single-line and perhaps even shorter, now it looks like the paragraph from a man page.

So I propose to move the new text to the sysctl(3) manpage where it belongs. Instead, single-liners from sysctl(3) might be used for the sysctl description lines.

sys/kern/kern_mib.c

192

dcons buffer is accounted on x86.

[rpokala]

As suggested, simplified the descriptions and added a pointer to the manpage.

[bcr]

OK from manpages. Thanks for doing the work.

[kib]

sys/kern/kern_mib.c

191

'; see sysctl(3)' is redundand, why kernel should lecture users how to use man(1) ? We do not do things like 'No such file or directory, see open(2)'.

[rpokala]

Remove the reference to sysctl(3) from the individual descriptions.