Add options COMPACT to produce smaller kernel

[mjg]

Summary

This adds __aligned_if_not_compact and converts __exclusive_cache_line to use it. It retains the section annotation, I may whack it.

I'm not interested in arguing about the name, propose something else and I'll rename. Alternatively, write your own patch and I'll use it in D27185

[kib]

sys/conf/options

1019

Not specifying file name means that option is stored in opt_compact.h, but you never include it.

I strongly suggest putting it in opt_global.h.

sys/sys/cdefs.h

244

This header is also used for userspace, and COMPACT is clearly is in user namespace.
Perhaps we need to use protected name for the option, like __COMPACT.

[mjg]

sys/sys/cdefs.h

244

so that would be __COMPACT put in the config? Looks like some form of prefixing would be warranted for cases like this.

I don't think the COMPACT option (with whatever name) is worth introducing at this time if it goes beyond the few lines (+ fixups) I posted here.

[kib]

sys/sys/cdefs.h

244

I think it should go somewhere in systm.h or similar. Then it could be COMPACT without prefix.

I do think that COMPAT is worth it, even if such small for now. It is first step, and I expect that it will be taken from this quite fast. It is long overdue.

[mjg]

So put together the following. This runs into further issues as users have to explicitly include opt_global to get the macro, so I think this is just too error prone in this form.

That said, I don't intend to work on this any further. If you want to see this option in you will have to take over or get someone else to do it.

[kib]

This looks fine to me as the first step.

There is no need to manually include opt_global.h, it is automatically pre-included by the build infrastructure: -include /usr/home/kostik/work/DEV/src/sys/amd64/compile/GENERIC/opt_global.h.

I wonder how much more can we pack in the first commit, e.g. mtx_padalign can be converted to __aligned_if_not_compact.

sys/sys/systm.h

159

Are there uses for 'x' or is x always CACHE_LINE_SIZE, for practical purposes ?