Re: [RFC PATCH 3/3] mm/memory-failure: handle min_order_for_split() error code properly

[David Hildenbrand (Red Hat)]

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