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

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Message-ID: <bec37700-8176-45b1-91b3-fb47420679ab@kernel.org>
Date: Thu, 20 Nov 2025 10:37:55 +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>, 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 04:59, 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

I'm wondering whether we should change min_order_for_split() to something like:

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7c69572b6c3f5..34eb6fec9a059 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4210,16 +4210,19 @@ int folio_split(struct folio *folio, unsigned int new_order,
                              SPLIT_TYPE_NON_UNIFORM);
  }

-int min_order_for_split(struct folio *folio)
+unsigned int min_order_for_split(struct folio *folio)
  {
         if (folio_test_anon(folio))
                 return 0;

+       /*
+        * If the folio got truncated, we don't know the previous mapping and
+        * consequently the old min order. But it doesn't matter, as any split
+        * attempt will immediately fail with -EBUSY as the folio cannot get
+        * split until freed.
+        */
         if (!folio->mapping) {
-               if (folio_test_pmd_mappable(folio))
-                       count_vm_event(THP_SPLIT_PAGE_FAILED);
-               return -EBUSY;
-       }
+               return 0;

         return mapping_min_folio_order(folio->mapping);
  }

-- 
Cheers

David