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

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Message-ID: <86CBD3DE-2245-4C79-BDA3-4977548898E3@nvidia.com>
Date: Thu, 20 Nov 2025 10:00:55 -0500
From: Zi Yan <ziy@...dia.com>
To: Balbir Singh <balbirs@...dia.com>
Cc: David Hildenbrand <david@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 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 19 Nov 2025, at 23:45, Balbir Singh wrote:

> 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?

The bit should be set. Anyway, I am going to take David’s approach to
change min_order_for_split().

Thanks.

>
>> +			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


Best Regards,
Yan, Zi