Re: three kernel patches for review

[Chris Pressey <cpressey@xxxxxxxxxxxxxxx>]

On Tue, 19 Apr 2005 18:48:02 -0700 (PDT)
Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx> wrote:

> [...]
>     Otherwise, the ANSIfication patch generally looks good, go ahead
>     and commit #1 after you clean up that comment.
> 
>     On #2 ... looks reasonable.  Commit away!

OK, committed!

>     On #3 ... that doesn't look so reasonable.  I suppose on a machine
>     with huge amounts of memory one might want such a mechanism, but
>     frankly if memory is bad (especially if it is ECC'd memory), the
>     only correct solution is to replace it.  

I'm going to call you on that one, Matt - _why_ do you say that is the
only correct solution?

My understanding of the service curve of RAM is that it is not like that
of disks.  Entropy does affect RAM, but at a much longer time-scale, so
the first few bad bits you see are much more likely to be flukes than an
indication that the RAM stick is reaching the end of its useful life.

Also, the conventional wisdom that the thing you should do when you have
bad bits in a stick of RAM is to replace the entire stick, sounds like
it stems from the fact that the OS has no way of remapping those bad
bits (like it has with a disk.)  Of course, with this patch, that fact
would no longer be a fact, and that wisdom wouldn't hold water anymore.

On Wed, 20 Apr 2005 10:24:37 +0200
Joerg Sonnenberger <joerg@xxxxxxxxxxxxxxxxx> wrote:

> I'm also split on the badram patch. I have some RAM modules which have
> static bad bits, so they could be used with the bad ram patch. On the
> other hand, such modules should be replaced and burned :)

Same question to you, Joerg - _why_ should they be replaced and burned?

When I consider the sheer amount of resources that go into manufacturing
a stick, and that there are typically millions of still-good bits that
could still be put to use on a "bad" one, I'd consider it a rotten shame
to just throw it out.

The Linux BadRAM project's website also lists some sound motivations,
including a commercial one:

  http://rick.vanrein.org/linux/badram/

Anyway, that's my case for including this patch.  If you still don't
think it should go in, I won't say anything further, but please do at
least consider the reasons I've given.

-Chris