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

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Message-ID: <aNI4QgvyoSrP9-K4@hpe.com>
Date: Tue, 23 Sep 2025 01:03:46 -0500
From: Kyle Meyer <kyle.meyer@....com>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: "Luck, Tony" <tony.luck@...el.com>, Jiaqi Yan <jiaqiyan@...gle.com>,
        David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
        corbet@....net, linmiaohe@...wei.com, shuah@...nel.org,
        jane.chu@...cle.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 Sun, Sep 21, 2025 at 05:06:31PM +0530, Anshuman Khandual wrote:
> 
> 
> On 18/09/25 1:24 AM, Luck, Tony wrote:
> > On Wed, Sep 17, 2025 at 12:32:47PM -0700, Jiaqi Yan wrote:
> >> +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.
> > 
> > So the expand the bitmask idea from earlier in this thread?
> > 
> > Bit0	0 = soft offline disabled. 1 = Enabled (but see other bits)
> > Bit1	0 = allow offline of 4K pages, 1 = suppress 4K offline
> > Bit2	0 = allow offline of hugetlb, 1 = suppress hugetlb offline
> > Bit3	0 = allow breakup of transparent huge pages to just offline 4K, 1 = suppress transparent breakup
> > Bit4+	Reserved for suppressing other page types we invent in the future
> > 
> > Values 0 and 1 keep their original meaning.
> > 
> > Value 5 means: offline 4K, keep hugetlb, breakup transparent huge pages.
> 
> This disable bitmask (but when generally enabled via bit[0] = 1) method
> seems much better. But I am not sure about page size being a valid page
> type classification though. Just to start with, defining first two bits
> in this bitmask should be good enough, which will atleast help document
> and validate this new interface properly.
> 
> Bit1	0 = allow offline of hugetlb, 1 = suppress hugetlb offline
> Bit2	0 = allow breakup of transparent huge pages to just offline base pages, 1 = suppress transparent breakup
> Bit3+	Reserved for suppressing other page types we invent in the future

The current patch is already applied to mm-git and supports the following bits:

    0 - Enable soft offline
    1 - Disable soft offline for HugeTLB pages

https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-new&id=9ae6eefa4b6bd3c3e7ef417a6507dce4b55101b4

Are any immediate changes needed?

Support for additional page types, such as transparent huge pages, can be added
later as needed.

Thanks,
Kyle Meyer