kernel memory checks on boot vs. boot time

[Ivan Voras]

On 23/03/2011 12:51, Andriy Gapon wrote:
> on 22/03/2011 21:54 Matthew Jacob said the following:
>> 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.
>>>
>>> If nothing else, I would definitely drop this from amd64 (all those systems
>>> have SMAP and machine check support, etc.).
>>>
>>>
>> Memory checks are definitely still useful. Loading the linux mem tester has
>> helped find lots of problems, even on so-called modern machines. I'd voter for
>> leaving this as an option.
>
> I think that you talk about a different kind of memory checking/testing.
> What we have in FreeBSD looks a lot like what BIOSes use(d) to do on startup.
> Besides, AFAIR, it doesn't report any results to you.

I'd say that is the main point. At least once I've thought the machine 
hung when it was doing this check for a surprisingly long time. I'd vote 
for *at least* adding a "twirling baton" indicator (every 1 GB or so) 
that something is going on, on all platforms :)

If these tests have any effect at all (how can they fail? has anyone 
seen them fail?) I'd vote to keep them enabled by default, with a 
tunable to optionally disable them, as every little bit helps for 
reliability. If there is no effect at all from the tests, then just 
remove them.