RE: [RFC PATCH] cxl: avoid duplicating report from MCE & device

["Luck, Tony" <tony.luck@intel.com>]

> So who actually cares about recovering poisoned volatile memory?
> I'd like to understand more on how significant a use case this is.
> Whilst I can conjecture that its an extreme case of wanting to avoid
> loosing the ability to create 1GiB or larger pages due to poison
> is that a real problem for anyone today?  Note this is just the case
> where you've reached an actual uncorrectable error and probably
> / possibly killed something, not the more common soft offlining
> of memory due to correctable errors being detected.

I guess you really need a reply from someone with a data center
with thousands of machines, since that's where this question
may be important.

My humble opinion is that, outside of the huge page issue, nobody
should try to recover a poisoned page. Systems that can report
and recover from poison have tens, hundreds, or more GBytes
of memory. Dropping 4K pages will not have any measurable
impact on a system (even if there are hundreds of pages dropped).

There's no reliable way to determine whether the poisoned page
was due to some transient issue, or a permanent defect. Recovering
a poisoned page runs the risk that the poison will re-occur. Perhaps
next use of the page will be in some unrecoverable (kernel) context.

So recovery has some risk, but very little upside benefit.

-Tony