meta mode

Hi,

I use meta-mode in /etc/src-env.conf so that if (for example) a small
change in the kernel config is made, the machine doesn't take hours recompiling.

Also, (I *think* it works this way) if src gets updated by git and 
world/kernel rebuilt it won't recompile already compiled files provided
I don't delete /usr/obj/*

But, from time to time, one might be required to make
cleanworld && make cleandir (to be sure) && make clean (to be *really* sure)

What circumstances & notices in /usr/src/UPDATING would require it?

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