Re: [PATCH v3 3/4] mm/memory-failure: improve large block size folio handling.

[David Hildenbrand <david@redhat.com>]

On 22.10.25 05:35, Zi Yan wrote:

Subject: I'd drop the trailing "."

> Large block size (LBS) folios cannot be split to order-0 folios but
> min_order_for_folio(). Current split fails directly, but that is not
> optimal. Split the folio to min_order_for_folio(), so that, after split,
> only the folio containing the poisoned page becomes unusable instead.
> 
> For soft offline, do not split the large folio if its min_order_for_folio()
> is not 0. Since the folio is still accessible from userspace and premature
> split might lead to potential performance loss.
> 
> Suggested-by: Jane Chu <jane.chu@oracle.com>
> Signed-off-by: Zi Yan <ziy@nvidia.com>

This is not a fix, correct? Because the fix for the issue we saw was 
sent out separately.

> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>   mm/memory-failure.c | 30 ++++++++++++++++++++++++++----
>   1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index f698df156bf8..40687b7aa8be 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1656,12 +1656,13 @@ static int identify_page_state(unsigned long pfn, struct page *p,
>    * there is still more to do, hence the page refcount we took earlier
>    * is still needed.
>    */
> -static int try_to_split_thp_page(struct page *page, bool release)
> +static int try_to_split_thp_page(struct page *page, unsigned int new_order,
> +		bool release)
>   {
>   	int ret;
>   
>   	lock_page(page);
> -	ret = split_huge_page(page);
> +	ret = split_huge_page_to_order(page, new_order);
>   	unlock_page(page);
>   
>   	if (ret && release)
> @@ -2280,6 +2281,9 @@ int memory_failure(unsigned long pfn, int flags)
>   	folio_unlock(folio);
>   
>   	if (folio_test_large(folio)) {
> +		int new_order = min_order_for_split(folio);

could be const

> +		int err;
> +
>   		/*
>   		 * The flag must be set after the refcount is bumped
>   		 * otherwise it may race with THP split.
> @@ -2294,7 +2298,15 @@ int memory_failure(unsigned long pfn, int flags)
>   		 * page is a valid handlable page.
>   		 */
>   		folio_set_has_hwpoisoned(folio);
> -		if (try_to_split_thp_page(p, false) < 0) {
> +		err = try_to_split_thp_page(p, new_order, /* release= */ false);
> +		/*
> +		 * If the folio cannot be split to order-0, kill the process,
> +		 * but split the folio anyway to minimize the amount of unusable
> +		 * pages.

You could briefly explain here that the remainder of memory failure 
handling code cannot deal with large folios, which is why we treat it 
just like failed split.

-- 
Cheers

David / dhildenb