I realized that two things can be separated. One is whether DIAGNOSTIC
turns on features that increase the size of memory allocations, which is
my real concern. The other is whether the KMEM_SIZE and KMEM_REDZONE
should be on by default in -current on various architectures, which is I
think your primary concern. On i386 and amd64, it may well be that the
performance change is not really noticeable. But increasing memory
sizes on small-memory architectures is something else. With these
rolled into DIAGNOSTIC, it becomes infeasible to enable the
invariant-checking part of DIAGNOSTIC without these on those
architectures.
So, I'd like you to still remove these from being auto-enabled, and add
them to src/sys/arch/{i386,amd64}/conf/GENERIC, and optionally on
whatever other arches make sense.
greg
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