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

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Message-ID: <2bd5c32b-dfc4-4345-8cc8-bbda5acdc596@oracle.com>
Date: Mon, 25 Aug 2025 15:36:54 -0700
From: jane.chu@...cle.com
To: Kyle Meyer <kyle.meyer@....com>, Miaohe Lin <linmiaohe@...wei.com>
Cc: 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 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?

>>>>>
>>>>> 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.
"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.

thanks!
-jane

> 
> Thanks,
> Kyle Meyer