Re: [PATCH v4 0/4] Userspace controls soft-offline pages

[Andi Kleen <ak@linux.intel.com>]

On Fri, Jun 21, 2024 at 04:53:41PM -0700, Jiaqi Yan wrote:
> Thanks for your comment, Andi.
> 
> On Thu, Jun 20, 2024 at 3:53 PM Andi Kleen <ak@linux.intel.com> wrote:
> >
> > Jiaqi Yan <jiaqiyan@google.com> writes:
> >
> > > Correctable memory errors are very common on servers with large
> > > amount of memory, and are corrected by ECC, but with two
> > > pain points to users:
> > > 1. Correction usually happens on the fly and adds latency overhead
> > > 2. Not-fully-proved theory states excessive correctable memory
> > >    errors can develop into uncorrectable memory error.
> >
> > This patchkit is amusing (or maybe sad) because it basically tries to
> > reconstruct the original soft offline design using a user space daemon
> > instead of doing policy badly in the kernel.
> 
> Some clarifications. I don't intend to reconstruct. I think this
> patchset can also be treated as "patch some missing places so that
> kernel doesn't soft offline behind the back of userspace daemon".
> I agree with you (IIUC) that the policy for corrected memory errors
> should exist in userspace. But the situation is that some behaviors in
> the kernel don't respect that (they either have a reason to not
> respect, or just forget to respect). enable_soft_offline is basically
> the big button in userspace to block these kernel violators.

It would be better to disable them earlier before they waste work
tracking things unnecessarily.  But yes it's a step in the right direction.

> 
> >
> > You can still have it by enabling CONFIG_X86_MCELOG_LEGACY and
> > use http://www.mcelog.org or an equivalent daemon of your chosing
> > that listens to /dev/mcelog.
> 
> If I didn't miss anything important in
> https://github.com/andikleen/mcelog and
> arch/x86/kernel/cpu/mce/dev-mcelog.c, I don't think /dev/mcelog works
> on ARM platforms where CPER is used to convey hw errors from platform
> to OS.

Yes or not on AMD even. 

-Andi