separating out memory checks from INVARIANTS

[Bruce Evans]

On Sat, 15 Mar 2008, Jeff Roberson wrote:

> On Sat, 15 Mar 2008, Kip Macy wrote:
>> Would it make it possible to do memory allocation without holding a
>> lock in the M_NOWAIT case?
>
> Yes, when I originally wrote the code it didn't require a lock because I 
> relied on byte writes being atomic.  However, we had platforms for which that 
> wasn't true. (alpha).  It may be that it's safe not to lock even now on 
> x86/amd64.  I don't know the specifics of the memory architectures on 
> powerpc, arm, mips, etc. though.

sparc64 only supports atomic ops on sizes 32 and 64 bits.  I think it
and not alpha was responsible for eliminating use of 8 and 16 bit
atomic ops in MI code.

My version of atomic.h for i386 only supports atomic ops on size 32.
8 and 16 bit atomic ops are not usable in MI code and are or were not
used in i386 MD code, so they are just interface bloat.

Bruce