linux-kernel - Re: [PATCH] mm/memory-failure: Disable soft offline for HugeTLB pages by default

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Message-ID: <749511a8-7c57-4f97-9e49-8ebe8befe9aa@redhat.com>
Date: Thu, 11 Sep 2025 10:46:10 +0200
From: David Hildenbrand <david@...hat.com>
To: Kyle Meyer <kyle.meyer@....com>, akpm@...ux-foundation.org,
 corbet@....net, linmiaohe@...wei.com, shuah@...nel.org, tony.luck@...el.com
Cc: Liam.Howlett@...cle.com, bp@...en8.de, hannes@...xchg.org, jack@...e.cz,
 jane.chu@...cle.com, jiaqiyan@...gle.com, 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] mm/memory-failure: Disable soft offline for HugeTLB pages
 by default

On 10.09.25 18:15, Kyle Meyer wrote:
> Soft offlining a HugeTLB page reduces the available HugeTLB page pool.
> Since HugeTLB pages are preallocated, reducing the available HugeTLB
> page pool can cause allocation failures.
> 
> /proc/sys/vm/enable_soft_offline provides a sysctl interface to
> disable/enable soft offline:
> 
> 0 - Soft offline is disabled.
> 1 - Soft offline is enabled.
> 
> The current sysctl interface does not distinguish between HugeTLB pages
> and other page types.
> 
> Disable soft offline for HugeTLB pages by default (1) and extend the
> sysctl interface to preserve existing behavior (2):
> 
> 0 - Soft offline is disabled.
> 1 - Soft offline is enabled (excluding HugeTLB pages).
> 2 - Soft offline is enabled (including HugeTLB pages).
> 
> Update documentation for the sysctl interface, reference the sysctl
> interface in the sysfs ABI documentation, and update HugeTLB soft
> offline selftests.

I'm sure you spotted that the documentation for 
"/sys/devices/system/memory/soft_offline_pag" resides under "testing".

If your read about MADV_SOFT_OFFLINE in the man page it clearly says:

"This feature is intended for testing of memory error-handling code; it 
is available  only if the kernel was configured with CONFIG_MEMORY_FAILURE."

So I'm sorry to say: I miss why we should add all this complexity to 
make a feature used for testing soft-offlining work differently for 
hugetlb folios -- with a testing interface.

-- 
Cheers

David / dhildenb