linux-kernel - Re: [PATCH] mm/memory-failure: Do not call action

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Message-ID: <aK0UTovxnKfjPwXs@hpe.com>
Date: Mon, 25 Aug 2025 20:56:30 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: jane.chu@...cle.com
Cc: Miaohe Lin <linmiaohe@...wei.com>, Jiaqi Yan <jiaqiyan@...gle.com>,
        akpm@...ux-foundation.org, david@...hat.com, tony.luck@...el.com,
        bp@...en8.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-edac@...r.kernel.org, lorenzo.stoakes@...cle.com,
        Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org,
        surenb@...gle.com, mhocko@...e.com, nao.horiguchi@...il.com,
        osalvador@...e.de
Subject: Re: [PATCH] mm/memory-failure: Do not call action_result() on
 already poisoned pages

On Mon, Aug 25, 2025 at 03:36:54PM -0700, jane.chu@...cle.com wrote:
> On 8/25/2025 9:09 AM, Kyle Meyer wrote:
> > On Mon, Aug 25, 2025 at 11:04:43AM +0800, Miaohe Lin wrote:
> > > On 2025/8/22 8:24, Jiaqi Yan wrote:
> > > > On Thu, Aug 21, 2025 at 12:36 PM Kyle Meyer <kyle.meyer@....com> wrote:
> > > > > 
> > > > > On Thu, Aug 21, 2025 at 11:23:48AM -0700, Jiaqi Yan wrote:
> > > > > > On Thu, Aug 21, 2025 at 9:46 AM Kyle Meyer <kyle.meyer@....com> wrote:
> > > > > > > 
> > > > > > > Calling action_result() on already poisoned pages causes issues:
> > > > > > > 
> > > > > > > * The amount of hardware corrupted memory is incorrectly incremented.
> > > > > > > * NUMA node memory failure statistics are incorrectly updated.
> > > > > > > * Redundant "already poisoned" messages are printed.
> 
> Assuming this means that the numbers reported from
>   /sys/devices/system/node/node*/memory_failure/*
> do not match certain expectation, right?
> 
> If so, could you clarify what is the expectation?

Sure, and please let me know if I'm mistaken.

Here's the description of total:

What:		/sys/devices/system/node/nodeX/memory_failure/total
Date:		January 2023
Contact:	Jiaqi Yan <jiaqiyan@...gle.com>
Description:
		The total number of raw poisoned pages (pages containing
		corrupted data due to memory errors) on a NUMA node.

That should emit the number of poisoned pages on NUMA node X. That's
incremented each time update_per_node_mf_stats() is called.

Here's the description of failed:

What:		/sys/devices/system/node/nodeX/memory_failure/failed
Date:		January 2023
Contact:	Jiaqi Yan <jiaqiyan@...gle.com>
Description:
		Of the raw poisoned pages on a NUMA node, how many pages are
		failed by memory error recovery attempt. This usually means
		a key recovery operation failed.

That should emit the number of poisoned pages on NUMA node X that could
not be recovered because the attempt failed. That's incremented each time
update_per_node_mf_stats() is called with MF_FAILED.

We're currently calling action_result() with MF_FAILED each time we encounter
a poisoned page (note: the huge page path is a bit different, we only call
action_result() with MF_FAILED when MF_ACTION_REQUIRED is set). That, IMO,
breaks the descriptions. We already incremented the per NUMA node MF statistics
to account for that poisoned page.

> > > > > > 
> > > > > > All agreed.
> > > > > > 
> > > > > > > 
> > > > > > > Do not call action_result() on already poisoned pages and drop unused
> > > > > > > MF_MSG_ALREADY_POISONED.
> > > > > > 
> > > > > > Hi Kyle,
> > > > > > 
> > > > > > Patch looks great to me, just one thought...
> > > 
> > > Thanks both.
> > > 
> > > > > > 
> > > > > > Alternatively, have you thought about keeping MF_MSG_ALREADY_POISONED
> > > > > > but changing action_result for MF_MSG_ALREADY_POISONED?
> > > > > > - don't num_poisoned_pages_inc(pfn)
> > > > > > - don't update_per_node_mf_stats(pfn, result)
> > > > > > - still pr_err("%#lx: recovery action for %s: %s\n", ...)
> > > > > > - meanwhile remove "pr_err("%#lx: already hardware poisoned\n", pfn)"
> > > > > > in memory_failure and try_memory_failure_hugetlb
> > > > > 
> > > > > I did consider that approach but I was concerned about passing
> > > > > MF_MSG_ALREADY_POISONED to action_result() with MF_FAILED. The message is a
> > > > > bit misleading.
> > > > 
> > > > Based on my reading the documentation for MF_* in static const char
> > > > *action_name[]...
> > > > 
> > > > Yeah, for file mapped pages, kernel may not have hole-punched or
> > > > truncated it from the file mapping (shmem and hugetlbfs for example)
> > > > but that still considered as MF_RECOVERED, so touching a page with
> > > > HWPoison flag doesn't mean that page was failed to be recovered
> > > > previously.
> > > > 
> > > > For pages intended to be taken out of the buddy system, touching a
> > > > page with HWPoison flag does imply it isn't isolated and hence
> > > > MF_FAILED.
> > > 
> > > There should be other cases that memory_failure failed to isolate the
> > > hwpoisoned pages at first time due to various reasons.
> > > 
> > > > 
> > > > In summary, seeing the HWPoison flag again doesn't necessarily
> > > > indicate what the recovery result was previously; it only indicate
> > > > kernel won't re-attempt to recover?
> > > 
> > > Yes, kernel won't re-attempt to or just cannot recover.
> > > 
> > > > 
> > > > > 
> > > > > How about introducing a new MF action result? Maybe MF_NONE? The message could
> > > > > look something like:
> > > > 
> > > > Adding MF_NONE sounds fine to me, as long as we correctly document its
> > > > meaning, which can be subtle.
> > > 
> > > Adding a new MF action result sounds good to me. But IMHO MF_NONE might not be that suitable
> > > as kill_accessing_process might be called to kill proc in this case, so it's not "NONE".
> > 
> > OK, would you like a separate MF action result for each case? Maybe
> > MF_ALREADY_POISONED and MF_ALREADY_POISONED_KILLED?
> > 
> > MF_ALREADY_POISONED can be the default and MF_ALREADY_POISONED_KILLED can be
> > used when kill_accessing_process() returns -EHWPOISON.
> > 
> > The log messages could look like...
> > 
> > Memory failure: 0xXXXXXXXX: recovery action for already poisoned page: None
> > 	and
> > Memory failure: 0xXXXXXXXX: recovery action for already poisoned page: Process killed
> 
> Agreed with Miaohe that "None" won't work.

What action is M-F() taking to recover already poisoned pages that don't have
MF_ACTION_REQUIRED set?

> "Process killed" sounds okay for MF_MSG_ALREADY_POISONED, but
> we need to understand why "Failed" doesn't work for your usecase.
> "Failed" means process is killed but page is not successfully isolated which
> applies to MF_MSG_ALREADY_POISONED case as well.

So that accessing process is killed. Why call action_result() with MF_FAILED?
Doesn't that indicate we poisoned another page and the recovery attempt failed?

Thanks,
Kyle Meyer