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

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Message-ID:
 <TYCPR01MB9617A2CC29E34D10B6B85ACFE52A2@TYCPR01MB9617.jpnprd01.prod.outlook.com>
Date: Fri, 29 Nov 2024 08:26:01 +0000
From: "Tomohiro Misono (Fujitsu)" <misono.tomohiro@...itsu.com>
To: 'Miaohe Lin' <linmiaohe@...wei.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 2024/11/28 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.

Regards,
Tomohiro Misono