linux-kernel - Re: [PATCH v2 2/3] mm/memory-failure: improve large block size folio handling.

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Message-ID: <CAHbLzkoOZm0PXxE9qwtF4gKR=cpRXrSrJ9V9Pm2DJexs985q4g@mail.gmail.com>
Date: Fri, 17 Oct 2025 12:11:17 -0700
From: Yang Shi <shy828301@...il.com>
To: Zi Yan <ziy@...dia.com>
Cc: linmiaohe@...wei.com, david@...hat.com, jane.chu@...cle.com, 
	kernel@...kajraghav.com, 
	syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com, 
	syzkaller-bugs@...glegroups.com, akpm@...ux-foundation.org, mcgrof@...nel.org, 
	nao.horiguchi@...il.com, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, 
	Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, Wei Yang <richard.weiyang@...il.com>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v2 2/3] mm/memory-failure: improve large block size folio handling.

On Wed, Oct 15, 2025 at 8:38 PM Zi Yan <ziy@...dia.com> 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.
>
> Suggested-by: Jane Chu <jane.chu@...cle.com>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  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) {

folio split will clear PG_has_hwpoisoned flag. It is ok for splitting
to order-0 folios because the PG_hwpoisoned flag is set on the
poisoned page. But if you split the folio to some smaller order large
folios, it seems you need to keep PG_has_hwpoisoned flag on the
poisoned folio.

Yang


> +                       /* 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 +2630,15 @@ static int soft_offline_in_use_page(struct page *page)
>         };
>
>         if (!huge && folio_test_large(folio)) {
> -               if (try_to_split_thp_page(page, true)) {
> +               int new_order = min_order_for_split(folio);
> +
> +               /*
> +                * If the folio cannot be split to order-0, do not split it at
> +                * all to retain the still accessible large folio.
> +                * NOTE: if getting free memory is perferred, split it like it
> +                * is done in memory_failure().
> +                */
> +               if (new_order || try_to_split_thp_page(page, new_order, true)) {
>                         pr_info("%#lx: thp split failed\n", pfn);
>                         return -EBUSY;
>                 }
> --
> 2.51.0
>
>