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

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Message-Id: <20250915201618.7d9d294a6b22e0f71540884b@linux-foundation.org>
Date: Mon, 15 Sep 2025 20:16:18 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Kyle Meyer <kyle.meyer@....com>
Cc: corbet@....net, david@...hat.com, 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 Mon, 15 Sep 2025 19:27:41 -0500 Kyle Meyer <kyle.meyer@....com> wrote:

> Soft offlining a HugeTLB page reduces the HugeTLB page pool.
> 
> Commit 56374430c5dfc ("mm/memory-failure: userspace controls soft-offlining pages")
> introduced the following sysctl interface to control soft offline:
> 
> /proc/sys/vm/enable_soft_offline
> 
> The interface does not distinguish between page types:
> 
>     0 - Soft offline is disabled
>     1 - Soft offline is enabled
> 
> Convert enable_soft_offline to a bitmask and support disabling soft
> offline for HugeTLB pages:
> 
> Bits:
> 
>     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)
> 
> Existing behavior is preserved.

um, why?  What benefit does this patch provide to our users? 
Use-cases, before-and-after scenarios, etc?

> Update documentation and HugeTLB soft offline self tests.
> 
> Reported-by: Shawn Fan <shawn.fan@...el.com>

Interesting.  What did Shawn report? (Closes:!).

> Suggested-by: Tony Luck <tony.luck@...el.com>
> Signed-off-by: Kyle Meyer <kyle.meyer@....com>
>
> ...
>
>  .../ABI/testing/sysfs-memory-page-offline     |  3 ++
>  Documentation/admin-guide/sysctl/vm.rst       | 28 ++++++++++++++++---
>  mm/memory-failure.c                           | 17 +++++++++--
>  .../selftests/mm/hugetlb-soft-offline.c       | 19 ++++++++++---
>  4 files changed, 56 insertions(+), 11 deletions(-)

I'll add it because testing, but please do explain why I added it?