linux-kernel - Re: [RFC PATCH 3/3] mm/memory-failure: handle min_order_for

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Message-ID: <b7af446a-eb74-483f-8a88-d48266278f05@nvidia.com>
Date: Thu, 20 Nov 2025 15:45:39 +1100
From: Balbir Singh <balbirs@...dia.com>
To: Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...nel.org>,
 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>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] mm/memory-failure: handle min_order_for_split()
 error code properly

On 11/20/25 14:59, 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.
> 
> Handle it properly by checking min_order_for_split() return value and not
> calling try_to_split_thp_page() if the value is negative. Add a comment
> in soft_offline_in_use_page() to clarify the possible negative new_order
> value.
> 
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
>  mm/memory-failure.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 7f908ad795ad..86582f030159 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2437,8 +2437,11 @@ int memory_failure(unsigned long pfn, int flags)
>  		 * or unhandlable page.  The refcount is bumped iff the
>  		 * page is a valid handlable page.
>  		 */
> -		folio_set_has_hwpoisoned(folio);
> -		err = try_to_split_thp_page(p, new_order, /* release= */ false);
> +		if (new_order >= 0) {
> +			folio_set_has_hwpoisoned(folio);

if new_order < 0, do we skip setting hwpoisioned bit on the folio?

> +			err = try_to_split_thp_page(p, new_order, /* release= */ false);
> +		} else
> +			err = new_order;
>  		/*
>  		 * If splitting a folio to order-0 fails, kill the process.
>  		 * Split the folio regardless to minimize unusable pages.
> @@ -2779,6 +2782,7 @@ static int soft_offline_in_use_page(struct page *page)
>  		/*
>  		 * If new_order (target split order) is not 0, do not split the
>  		 * folio at all to retain the still accessible large folio.
> +		 * new_order can be -EBUSY, meaning the folio cannot be split.
>  		 * NOTE: if minimizing the number of soft offline pages is
>  		 * preferred, split it to non-zero new_order like it is done in
>  		 * memory_failure().

Balbir