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

Jiaqi Yan
2025-09-17T19:33:00Z

On Wed, Sep 17, 2025 at 12:05 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 17.09.25 20:51, Kyle Meyer wrote:
> > 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?
>
> Hmm, at least I don't particularly like that. For each new exception we

+1. Given /proc/sys/vm/enable_soft_offline is extensible, I would
prefer a compact userspace API.

> would create a new file, and the file has weird semantics such that it
> has no meaning when enable_soft_offline=0.
>
> --
> Cheers
>
> David / dhildenb
>