Re: [PATCH v2] mm/memory-failure: Support disabling soft offline for HugeTLB pages

Kyle Meyer
2025-09-17T18:52:51Z

On Wed, Sep 17, 2025 at 09:02:55AM +0200, David Hildenbrand wrote:
>
> > > +
> > > + 0 - Enable soft offline
> > > + 1 - Disable soft offline for HugeTLB pages
> > > +
> > > +Supported values::
> > > +
> > > + 0 - Soft offline is disabled
> > > + 1 - Soft offline is enabled
> > > + 3 - Soft offline is enabled (disabled for HugeTLB pages)
> >
> > This looks very adhoc even though existing behavior is preserved.
> >
> > - Are HugeTLB pages the only page types to be considered ?
> > - How the remaining bits here are going to be used later ?
> >
>
> What I proposed (that could be better documented here) is that all other
> bits except the first one will be a disable mask when bit 0 is set.
>
> 2 - ... but yet disabled for hugetlb
> 4 - ... but yet disabled for $WHATEVER
> 8 - ... but yet disabled for $WHATEVERELSE
>
> > Also without a bit-wise usage roadmap, is not changing a procfs
> > interface (ABI) bit problematic ?
>
> For now we failed setting it to values that are neither 0 or 1, IIUC
> set_enable_soft_offline() correctly?

Yes, -EINVAL will be returned.

> So there should not be any problem, or which scenario do you have in mind?

Here's an alternative approach.

Do not modify the existing sysctl parameter:

/proc/sys/vm/enable_soft_offline

0 - Soft offline is disabled
1 - Soft offline is enabled

Instead, introduce a new sysctl parameter:

/proc/sys/vm/enable_soft_offline_hugetlb

0 - Soft offline is disabled for HugeTLB pages
1 - Soft offline is enabled for HugeTLB pages

and note in documentation that this setting only takes effect if
enable_soft_offline is enabled.

Anshuman (and David), would you prefer this?

Thanks,
Kyle Meyer