linux-kernel - Re: [PATCH] mm/memory_hotplug: fix dead loop in offline

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Message-ID: <ae2e301d-21ae-bf25-57b5-b9be9777bfe2@redhat.com>
Date:   Fri, 28 Apr 2023 18:22:38 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>, Yajun Deng <yajun.deng@...ux.dev>
Cc:     osalvador@...e.de, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/memory_hotplug: fix dead loop in offline_pages()

On 28.04.23 13:07, Michal Hocko wrote:
> On Fri 28-04-23 18:08:46, Yajun Deng wrote:
>> When migration failure in do_migrate_range() and then the
>> scan_movable_pages() will most likely return the same movable pfn.
>> In this case, there is no condition to bail out, they will
>> always run like this:
>>
>> ...
>> [878020.623959] migrating pfn 1727813 failed ret:1
>> [878020.623960] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813
>> [878020.623962] memcg:ffffa0ff82d5a000
>> [878020.623962] aops:def_blk_aops ino:fd00001
>> [878020.623964] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff)
>> [878020.623966] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018
>> [878020.623967] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000
>> [878020.623968] page dumped because: migration failure
>> [878020.626196] migrating pfn 1727813 failed ret:1
>> [878020.626198] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813
>> [878020.626200] memcg:ffffa0ff82d5a000
>> [878020.626200] aops:def_blk_aops ino:fd00001
>> [878020.626202] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff)
>> [878020.626204] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018
>> [878020.626205] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000
>> [878020.626206] page dumped because: migration failure
>> ...
>>
>> Bail out when migration failures reach 3 times.
>>
>> Fixes: bb8965bd82fd ("mm, memory_hotplug: deobfuscate migration part of offlining")
>> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> 
> Any hard coded failure retry limit will lead to premature failures. Have
> a look at 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too
> early"). A proper way to deal with this is to implement termination from
> the userspace (e.g. timeout $TIMEOUT /bin/echo 0 > $PATH_TO_MEM/online)
> Nacked-by: Michal Hocko <mhocko@...e.com>

Agreed; it's a bit more complicated when offlining is triggered by ACPI 
code :(

-- 
Thanks,

David / dhildenb