[PATCH v5 2/3] mm/memory-failure: improve large block size folio handling.

Zi Yan
2025-10-31T16:19:37Z

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>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
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;
}
--
2.51.0