Re: [PATCH 2/2] mm/memory-failure: improve large block size folio handling.

[Miaohe Lin <linmiaohe@huawei.com>]

On 2025/10/11 1:39, Zi Yan wrote:
> 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 it cannot be split to
> order-0. Since the folio is still accessible from userspace and premature
> split might lead to potential performance loss.

Thanks for your patch.

> 
> Suggested-by: Jane Chu <jane.chu@oracle.com>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
>  mm/memory-failure.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index f698df156bf8..443df9581c24 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_list_to_order(page, NULL, new_order);
>  	unlock_page(page);
>  
>  	if (ret && release)
> @@ -2280,6 +2281,7 @@ int memory_failure(unsigned long pfn, int flags)
>  	folio_unlock(folio);
>  
>  	if (folio_test_large(folio)) {
> +		int new_order = min_order_for_split(folio);
>  		/*
>  		 * The flag must be set after the refcount is bumped
>  		 * otherwise it may race with THP split.
> @@ -2294,7 +2296,14 @@ 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) {
> +		/*
> +		 * If the folio cannot be split to order-0, kill the process,
> +		 * but split the folio anyway to minimize the amount of unusable
> +		 * pages.
> +		 */
> +		if (try_to_split_thp_page(p, new_order, false) || new_order) {
> +			/* get folio again in case the original one is split */
> +			folio = page_folio(p);

If original folio A is split and the after-split new folio is B (A != B), will the
refcnt of folio A held above be missing? I.e. get_hwpoison_page() held the extra refcnt
of folio A, but we put the refcnt of folio B below. Is this a problem or am I miss
something?

Thanks.
.