+ mm-memory-failure-improve-large-block-size-folio-handling.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/memory-failure: improve large block size folio handling.
has been added to the -mm mm-new branch.  Its filename is
     mm-memory-failure-improve-large-block-size-folio-handling.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-failure-improve-large-block-size-folio-handling.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: mm/memory-failure: improve large block size folio handling.
Date: Wed, 29 Oct 2025 21:40:19 -0400

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.

Link: https://lkml.kernel.org/r/20251030014020.475659-3-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Suggested-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Pankaj Raghav <kernel@pankajraghav.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |   31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

--- a/mm/memory-failure.c~mm-memory-failure-improve-large-block-size-folio-handling
+++ a/mm/memory-failure.c
@@ -1656,12 +1656,13 @@ static int identify_page_state(unsigned
  * 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 @@ try_again:
 	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 @@ try_again:
 		 * 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(stru
 	};
 
 	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;
 		}
_

Patches currently in -mm which might be from ziy@nvidia.com are

mm-huge_memory-do-not-change-split_huge_page-target-order-silently.patch
mm-huge_memory-preserve-pg_has_hwpoisoned-if-a-folio-is-split-to-0-order.patch
mm-huge_memory-add-split_huge_page_to_order.patch
mm-memory-failure-improve-large-block-size-folio-handling.patch
mm-huge_memory-fix-kernel-doc-comments-for-folio_split-and-related.patch