Re: PATCH v3 ACPI: APEI: GHES: Don't offline huge pages just because BIOS asked

[jane.chu@oracle.com]

On 9/5/2025 12:58 PM, Luck, Tony wrote:
>> So the issue is the result of inaccurate MCA record about per rank CE
>> threshold being crossed. If OS offline the indicted page, it might be
>> signaled to offline another 4K page in the same rank upon access.
> 
> It appears that the BIOS that resulted in this report sensibly treats crossing
> the rank error threshold as needing a one-time report via GHES.
> 
>> Both MCA and offline-op are performance hitter, and as argued by this
>> patch, offline doesn't help except loosing a already corrected page.
>>
>> Here we choose to bypass hugetlb page simply because it's huge.  Is it
>> possible to argue that because the page is huge, it's less likely to get
>> another MCA on another page from the same rank?
> 
> If there really is a problem with the rank, it likely affects most pages (or
> at least most pages on the same NUMA node) because memory access
> is (usually) interleaved between channels, and accesses within a 4K page
> may hash to different ranks withing a channel.
> 
>> A while back this patch
>> 56374430c5dfc mm/memory-failure: userspace controls soft-offlining pages
>> has provided userspace control over whether to soft offline, could it be
>> a more preferable option?
> 
> Thanks for pointing that one out. I'll feed that back to the original reporter
> and see if it is an acceptable solution.
> 
>> I don't know, the patch itself is fine, it's the issue that it has
>> exposed that is more concerning.
> 
> Agreed. The root problem is the BIOS using this threshold reporting
> mechanism, without there being a way for the OS to determine the
> scope of memory affected by the threshold.
> 
> When this was originally implemented, the expectation was that the
> scope would be a 4K page.

Thanks!

BTW, forgot to ask another question.
	ghes_do_proc
	  bool sync = is_hest_sync_notify(ghes);
	  [..]
		queued = ghes_handle_memory_failure(gdata, sev, sync);
	  [..]
	  if (sync && !queued) {
	      force_sig(SIGBUS);
The question is, in the CE MCE case, 'sync' is never 'true' by design, 
correct?

thanks,
-jane


	
	


> 
> -Tony