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

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Message-ID: <aMsDJ3EU1zVJ00cX@hpe.com>
Date: Wed, 17 Sep 2025 13:51:19 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: David Hildenbrand <david@...hat.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>, akpm@...ux-foundation.org,
        corbet@....net, linmiaohe@...wei.com, shuah@...nel.org,
        tony.luck@...el.com, jane.chu@...cle.com, jiaqiyan@...gle.com,
        Liam.Howlett@...cle.com, bp@...en8.de, hannes@...xchg.org,
        jack@...e.cz, joel.granados@...nel.org, laoar.shao@...il.com,
        lorenzo.stoakes@...cle.com, mclapinski@...gle.com, mhocko@...e.com,
        nao.horiguchi@...il.com, osalvador@...e.de, rafael.j.wysocki@...el.com,
        rppt@...nel.org, russ.anderson@....com, shawn.fan@...el.com,
        surenb@...gle.com, vbabka@...e.cz, linux-acpi@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] mm/memory-failure: Support disabling soft offline for
 HugeTLB pages

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