linux-kernel - Re: [RFC PATCH] mm: memory-failure: add soft-offline stat in mf

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Message-ID: <cc401793-5ef6-55db-0028-728b865e33e0@huawei.com>
Date: Fri, 29 Nov 2024 17:07:10 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: "Tomohiro Misono (Fujitsu)" <misono.tomohiro@...itsu.com>, 'Jiaqi Yan'
	<jiaqiyan@...gle.com>
CC: "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [RFC PATCH] mm: memory-failure: add soft-offline stat in mf_stats

On 2024/11/29 16:26, Tomohiro Misono (Fujitsu) wrote:
>> On 2024/11/28 13:46, Tomohiro Misono (Fujitsu) wrote:
>>>>>> On 2024/11/21 12:55, Tomohiro Misono wrote:
>>>>>>> commit 44b8f8bf2438 ("mm: memory-failure: add memory failure stats
>>>>>>
>>>>>> Sorry for late, I've been swamped recently.
>>>>>
>>>>> Hi,
>>>>> Thanks for your comments.
>>>>>
>>>>>>
>>>>>>> to sysfs") introduces per NUMA memory error stats which show
>>>>>>> breakdown of HardwareCorrupted of /proc/meminfo in
>>>>>>> /sys/devices/system/node/nodeX/memory_failure.
>>>>>>
>>>>>> Thanks for your patch.
>>>>>>
>>>>>>>
>>>>>>> However, HardwareCorrupted also counts soft-offline pages. So, add
>>>>>>> soft-offline stats in mf_stats too to represent more accurate status.
>>>>>>
>>>>>> Adding soft-offline stats makes sense to me.
>>>>>
>>>>> Thanks for confirming.
>>>>
>>>> Agreed with Miaohe.
>>>>
>>>>>
>>>>>>
>>>>>>>
>>>>>>> This updates total count as:
>>>>>>>   total = recovered + ignored + failed + delayed + soft_offline>
>>>>>>> Test example:
>>>>>>> 1) # grep HardwareCorrupted /proc/meminfo
>>>>>>>      HardwareCorrupted:     0 kB
>>>>>>> 2) soft-offline 1 page by madvise(MADV_SOFT_OFFLINE)
>>>>>>> 3) # grep HardwareCorrupted /proc/meminfo
>>>>>>>      HardwareCorrupted:     4 kB
>>>>>>>    # grep -r "" /sys/devices/system/node/node0/memory_failure
>>>>>>>    /sys/devices/system/node/node0/memory_failure/total:1
>>>>>>>    /sys/devices/system/node/node0/memory_failure/soft_offline:1
>>>>>>>    /sys/devices/system/node/node0/memory_failure/recovered:0
>>>>>>>    /sys/devices/system/node/node0/memory_failure/ignored:0
>>>>>>>    /sys/devices/system/node/node0/memory_failure/failed:0
>>>>>>>    /sys/devices/system/node/node0/memory_failure/delayed:0
>>>>>>>
>>>>>>> Signed-off-by: Tomohiro Misono <misono.tomohiro@...itsu.com>
>>>>>>> ---
>>>>>>> Hello
>>>>>>>
>>>>>>> This is RFC because I'm not sure adding SOFT_OFFLINE in enum
>>>>>>> mf_result is a right approach. Also, maybe is it better to move
>>>>>>> update_per_node_mf_stats() into num_poisoned_pages_inc()?
>>>>>>>
>>>>>>> I omitted some cleanups and sysfs doc update in this version to
>>>>>>> highlight changes. I'd appreciate any suggestions.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Tomohiro Misono
>>>>>>>
>>>>>>>  include/linux/mm.h     | 2 ++
>>>>>>>  include/linux/mmzone.h | 4 +++-
>>>>>>>  mm/memory-failure.c    | 9 +++++++++
>>>>>>>  3 files changed, 14 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>>>>> index 5d6cd523c7c0..7f93f6883760 100644
>>>>>>> --- a/include/linux/mm.h
>>>>>>> +++ b/include/linux/mm.h
>>>>>>> @@ -3991,6 +3991,8 @@ enum mf_result {
>>>>>>>     MF_FAILED,      /* Error: handling failed */
>>>>>>>     MF_DELAYED,     /* Will be handled later */
>>>>>>>     MF_RECOVERED,   /* Successfully recovered */
>>>>>>> +
>>>>>>> +   MF_RES_SOFT_OFFLINE, /* Soft-offline */
>>>>>>
>>>>>> It might not be a good idea to add MF_RES_SOFT_OFFLINE here. 'mf_result' is used to record
>>>>>> the result of memory failure handler. So it might be inappropriate to add MF_RES_SOFT_OFFLINE
>> here.
>>>>>
>>>>> Understood. As I don't see other suitable place to put ENUM value, how about changing like below?
>>>>> Or, do you prefer adding another ENUM type instead of this?
>>>>
>>>> I think SOFT_OFFLINE-ed is one of the results of successfully
>>>> recovered, and the other one is HARD_OFFLINE-ed. So how about make a
>>>> separate sub-ENUM for MF_RECOVERED? Something like:
>>>
>>> Thanks for the suggestion.
>>>
>>>>
>>>> enum mf_recovered_result {
>>>>   MF_RECOVERED_SOFT_OFFLINE,
>>>>   MF_RECOVERED_HARD_OFFLINE,
>>>> };
>>>
>>> Ok.
>>>
>>>>
>>>> And
>>>> 1. total = recovered + ignored + failed + delayed
>>>> 2. recovered = soft_offline + hard_offline
>>>
>>> Do you mean mf_stats now have 7 entries in sysfs?
>>> (total, ignored, failed, delayed, recovered, hard_offline, soft_offline, then recovered = hard_offline +
>> soft_offline)
>>> Or 6 entries ? (in that case, hard_offline = recovered - soft_offline)
>>> It might be simpler to understand for user if total is just the sum of other entries like this RFC,
>>> but I'd like to know other opinions.
>>
>> Will it be better to have below items?
>> "
>> total
>> ignored
>> failed
>> dalayed
>> hard_offline
>> soft_offline
>> "
>>
>> though this will break the previous interface.
>> Any thoughts?
> 
> That would be great, but these files are under stable ABI and 
> I don't think we can change them, right?
> 
> https://docs.kernel.org/admin-guide/abi-stable.html
> Userspace programs are free to use these interfaces with no restrictions, and backward
> compatibility for them will be guaranteed for at least 2 years.
> Most interfaces (like syscalls) are expected to never change and always be available.

Thanks for your information. So we need to propose a better solution. Looking forward to hearing more suggestions.

Thanks.
.

> 
> Regards,
> Tomohiro Misono
>