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

[Shiyang Ruan <ruansy.fnst@fujitsu.com>]

在 2024/6/22 4:44, Luck, Tony 写道:
>> 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.

Since the hardware provides the instruction(CPU)/command(CXL) to clear 
the poison, we could make the function work, at least as an optional 
feature.  Then users could decide to use it or not after evaluating the 
risk and benefit.

I think doing recovery is an improvement step, and may need a lot of 
discussion.  I'm not sure if we could reach a conclusion in this thread. 
  Just hope more comments on the original problem (duplicate report) to 
solve in this patch.


--
Thanks,
Ruan.

> 
> -Tony