Re: [PATCH] mm/Kconfig: allow user to select MIGRATION if MEMORY_FAILURE is enabled

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Wed, Aug 12, 2026 at 07:55:29PM +0800, Xie Yuanbin wrote:
> On Wed, 12 Aug 2026 11:53:29 +0100, Lorenzo Stoakes (ARM) wrote:
> > But you seem to be implying the two options cannot both be enabled, that's
> > untrue:
> >
> > $ grep CONFIG_MIGRATION .config
> > CONFIG_MIGRATION=y
> > $ grep CONFIG_MEMORY_FAILURE .config
> > CONFIG_MEMORY_FAILURE=y
> >
> > Have you disabled compaction somehow?
> >
> > It sounds like your .config is broken and... you need to fix it yourself not
> > edit mm/Kconfig?
> >
> > If not you need to spell out exactly what config it is you have where you must
> > not have one of the things that select migration, but do want it anyway.
> >
> > I'm not sure we'd even support that?
> >
> > Right now:
> >
> >	CONFIG_COMPACTION (!)
> >	CONFIG_MEMORY_HOTREMOVE
> >	CONFIG_NUMA_MIGRATION
> >	CONFIG_CMA
> >
> > All select CONFIG_MIGRATION. Why is it that you cannot select one of these?
>
> As you say, currently, MEMORY_FAILURE and MIGRATION can be both
> enabled, however, you must enable one of the following configs
> at the same time:
> 	CONFIG_COMPACTION
> 	CONFIG_MEMORY_HOTREMOVE
> 	CONFIG_NUMA_MIGRATION
> 	CONFIG_CMA
>
> However, for embedded devices, these configs are not always enabled, and
> they can indeed be manually disable. This is the actual situation I am
> currently encountering.

Hmm really? It's a small embedded system that still needs to defragment for
large folios?

But...

>
> > What
> > weird config needs CONFIG_COMPACTION disabled but does want migration just for
> > soft offline debugging?
>
> It is not for debugging, but a real configuration in the production environment:
> 	CONFIG_COMPACTION=n
> 	CONFIG_MEMORY_HOTREMOVE=n
> 	CONFIG_NUMA=n
> 	CONFIG_CMA=n
> 	CONFIG_MEMORY_FAILURE=y
>
> > Users shouldn't select this at all. And this is an absolutely horrible way of
> > resolving whatever your real configuration issue is.
> >
> > I hate hate hate this. This is just completely the wrong resolution.
>
> What abort making MEMORY_FAILURE select MIGRATION, just like what Mike
> Rapoport said? If it's not appropriate no matter what, then let's stop
> discussing this patch as if it was never submitted. I'm sorry about that.

...reality trumps theory, so if this is really a config you need, Mike's
approach seems the least worst way.

So respin with something that just adds a select CONFIG_MIGRATION there and
please put a description of your real world use case in the commit
message.

I doubt there are users who would find the combination problematic.

>
> Thanks very much.

--
Cheers, Lorenzo