Re: [PATCH] mm/memory_hotplug: fix dead loop in offline_pages()

[David Hildenbrand]

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@xxxxxxxxx>
>
> 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@xxxxxxxx>

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

--
Thanks,

David / dhildenb