kernel memory checks on boot vs. boot time

[Ed Maste]

On Tue, Mar 22, 2011 at 03:51:13PM -0400, John Baldwin wrote:

> Do other platforms bother with these sorts of memory tests?  If not I'd vote 
> to just drop it.  I think this mattered more when you didn't have things like 
> SMAP (so you had to guess at where memory ended sometimes).  Also, modern 
> server class x86 machines generally support ECC RAM which will trigger a 
> machine check if there is a problem.  I doubt that the early checks are 
> catching anything even for the non-ECC case.

In the common case at work we want this off to reduce boot time.  The
desire for a tunable though that can add extended memory tests is to be
able to use the FreeBSD startup code as a replacement for memtest86+,
for a couple of reasons:

- FreeBSD's serial console output is more easily parsed by automated
  tools
- Memtest86+ appears to be limited to 64GB of RAM at the moment
- Memtest86+ lacks support for the Tylersburg architecture last I looked

-Ed