Re: [PATCH v4 4/6] mm/memory-hotplug: add finite retries in offline_pages() if migration fails

[Joanne Koong <joannelkoong@gmail.com>]

On Fri, Nov 8, 2024 at 1:27 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> On Fri, Nov 08, 2024 at 08:00:25PM +0100, David Hildenbrand wrote:
> > On 08.11.24 19:56, David Hildenbrand wrote:
> > > On 08.11.24 18:33, SeongJae Park wrote:
> > > > + David Hildenbrand
> > > >
> > > > On Thu, 7 Nov 2024 15:56:12 -0800 Joanne Koong <joannelkoong@gmail.com> wrote:
> > > >
> > > > > In offline_pages(), do_migrate_range() may potentially retry forever if
> > > > > the migration fails. Add a return value for do_migrate_range(), and
> > > > > allow offline_page() to try migrating pages 5 times before erroring
> > > > > out, similar to how migration failures in __alloc_contig_migrate_range()
> > > > > is handled.
> > > >
> > > > I'm curious if this could cause unexpected behavioral differences to memory
> > > > hotplugging users, and how '5' is chosen.  Could you please enlighten me?
> > > >
> > >
> > > I'm wondering how much more often I'll have to nack such a patch. :)
> >
> > A more recent discussion: https://lore.kernel.org/linux-mm/52161997-15aa-4093-a573-3bfd8da14ff1@fujitsu.com/T/#mdda39b2956a11c46f8da8796f9612ac007edbdab
> >
> > Long story short: this is expected and documented
>
> Thanks David for the background.
>
> Joanne, simply drop this patch. It is not required for your series.

Awesome, I'm happy to drop this patch.

Just curious though - don't we need this in order to mitigate the
scenario where if an unprivileged fuse server never completes
writeback, we don't run into this infinite loop? Or is it that memory
hotplugging is always initiated from userspace so if it does run into
an infinite loop (like also in that thread David linked), userspace is
responsible for sending a signal to terminate it?


Thanks,
Joanne