linux-kernel - Re: [PATCH v2 3/4] mm/huge_memory: make min_order_for

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Message-ID: <257c778f-1997-4986-8a6b-ae42bffc46d6@kernel.org>
Date: Mon, 24 Nov 2025 11:43:03 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Zi Yan <ziy@...dia.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 Miaohe Lin <linmiaohe@...wei.com>, Naoya Horiguchi
 <nao.horiguchi@...il.com>, Wei Yang <richard.weiyang@...il.com>,
 Balbir Singh <balbirs@...dia.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] mm/huge_memory: make min_order_for_split() always
 return an order

On 11/22/25 03:55, Zi Yan wrote:
> min_order_for_split() returns -EBUSY when the folio is truncated and cannot
> be split. In commit 77008e1b2ef7 ("mm/huge_memory: do not change
> split_huge_page*() target order silently"), memory_failure() does not
> handle it and pass -EBUSY to try_to_split_thp_page() directly.
> try_to_split_thp_page() returns -EINVAL since -EBUSY becomes 0xfffffff0 as
> new_order is unsigned int in __folio_split() and this large new_order is
> rejected as an invalid input. The code does not cause a bug.
> soft_offline_in_use_page() also uses min_order_for_split() but it always
> passes 0 as new_order for split.
> 
> Fix it by making min_order_for_split() always return an order. When the
> given folio is truncated, namely folio->mapping == NULL, return 0 and let
> a subsequent split function handle the situation and return -EBUSY.
> 
> Add kernel-doc to min_order_for_split() to clarify its use.
> 
> Signed-off-by: Zi Yan <ziy@...dia.com>

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

-- 
Cheers

David