Re: [PATCH v2 3/4] mm/huge_memory: make min_order_for_split() always return an order

[Wei Yang]

On Fri, Nov 21, 2025 at 09:55:28PM -0500, 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@xxxxxxxxxx>

LGTM, Thanks

Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxx>

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Wei Yang
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