Re: [PATCH v4 2/3] mm/memory-failure: improve large block size folio handling.

[Lance Yang <lance.yang@linux.dev>]

On 2025/10/30 09:40, 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 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>
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---

LGTM! Feel free to add:

Reviewed-by: Lance Yang <lance.yang@linux.dev>

>   mm/memory-failure.c | 31 +++++++++++++++++++++++++++----
>   1 file changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index f698df156bf8..acc35c881547 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)) {
> +		const int new_order = min_order_for_split(folio);
> +		int err;
> +
>   		/*
>   		 * The flag must be set after the refcount is bumped
>   		 * otherwise it may race with THP split.
> @@ -2294,7 +2298,16 @@ 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 splitting a folio to order-0 fails, kill the process.
> +		 * Split the folio regardless to minimize unusable pages.
> +		 * Because the memory failure code cannot handle large
> +		 * folios, this split is always treated as if it failed.
> +		 */
> +		if (err || new_order) {
> +			/* get folio again in case the original one is split */
> +			folio = page_folio(p);
>   			res = -EHWPOISON;
>   			kill_procs_now(p, pfn, flags, folio);
>   			put_page(p);
> @@ -2621,7 +2634,17 @@ static int soft_offline_in_use_page(struct page *page)
>   	};
>   
>   	if (!huge && folio_test_large(folio)) {
> -		if (try_to_split_thp_page(page, true)) {
> +		const int new_order = min_order_for_split(folio);
> +
> +		/*
> +		 * If new_order (target split order) is not 0, do not split the
> +		 * folio at all to retain the still accessible large folio.
> +		 * NOTE: if minimizing the number of soft offline pages is
> +		 * preferred, split it to non-zero new_order like it is done in
> +		 * memory_failure().
> +		 */
> +		if (new_order || try_to_split_thp_page(page, /* new_order= */ 0,
> +						       /* release= */ true)) {
>   			pr_info("%#lx: thp split failed\n", pfn);
>   			return -EBUSY;
>   		}