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

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Message-ID: <aMsR4Tr9ov1pfucC@agluck-desk3>
Date: Wed, 17 Sep 2025 12:54:09 -0700
From: "Luck, Tony" <tony.luck@...el.com>
To: Jiaqi Yan <jiaqiyan@...gle.com>
CC: David Hildenbrand <david@...hat.com>, Kyle Meyer <kyle.meyer@....com>,
	Anshuman Khandual <anshuman.khandual@....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>,
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	<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 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.

-Tony