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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , "Matthew Wilcox (Oracle)" , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 1/2] mm/huge_memory: do not change split_huge_page*() target order silently. 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charset="utf-8" Page cache folios from a file system that support large block size (LBS) can have minimal folio order greater than 0, thus a high order folio might not be able to be split down to order-0. Commit e220917fa507 ("mm: split a folio in minimum folio order chunks") bumps the target order of split_huge_page*() to the minimum allowed order when splitting a LBS folio. This causes confusion for some split_huge_page*() callers like memory failure handling code, since they expect after-split folios all have order-0 when split succeeds but in really get min_order_for_split() order folios. Fix it by failing a split if the folio cannot be split to the target order. Fixes: e220917fa507 ("mm: split a folio in minimum folio order chunks") [The test poisons LBS folios, which cannot be split to order-0 folios, and also tries to poison all memory. The non split LBS folios take more memory than the test anticipated, leading to OOM. The patch fixed the kernel warning and the test needs some change to avoid OOM.] Reported-by: syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68d2c943.a70a0220.1b52b.02b3.GAE@google= .com/ Signed-off-by: Zi Yan Reviewed-by: Luis Chamberlain Reviewed-by: Pankaj Raghav --- include/linux/huge_mm.h | 28 +++++----------------------- mm/huge_memory.c | 9 +-------- mm/truncate.c | 6 ++++-- 3 files changed, 10 insertions(+), 33 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 8eec7a2a977b..9950cda1526a 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -394,34 +394,16 @@ static inline int split_huge_page_to_list_to_order(st= ruct page *page, struct lis * Return: 0: split is successful, otherwise split failed. */ static inline int try_folio_split(struct folio *folio, struct page *page, - struct list_head *list) + struct list_head *list, unsigned int order) { - int ret =3D min_order_for_split(folio); - - if (ret < 0) - return ret; - - if (!non_uniform_split_supported(folio, 0, false)) + if (!non_uniform_split_supported(folio, order, false)) return split_huge_page_to_list_to_order(&folio->page, list, - ret); - return folio_split(folio, ret, page, list); + order); + return folio_split(folio, order, page, list); } static inline int split_huge_page(struct page *page) { - struct folio *folio =3D page_folio(page); - int ret =3D min_order_for_split(folio); - - if (ret < 0) - return ret; - - /* - * split_huge_page() locks the page before splitting and - * expects the same page that has been split to be locked when - * returned. split_folio(page_folio(page)) cannot be used here - * because it converts the page to folio and passes the head - * page to be split. - */ - return split_huge_page_to_list_to_order(page, NULL, ret); + return split_huge_page_to_list_to_order(page, NULL, 0); } void deferred_split_folio(struct folio *folio, bool partially_mapped); =20 diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 0fb4af604657..af06ee6d2206 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3829,8 +3829,6 @@ static int __folio_split(struct folio *folio, unsigne= d int new_order, =20 min_order =3D mapping_min_folio_order(folio->mapping); if (new_order < min_order) { - VM_WARN_ONCE(1, "Cannot split mapped folio below min-order: %u", - min_order); ret =3D -EINVAL; goto out; } @@ -4173,12 +4171,7 @@ int min_order_for_split(struct folio *folio) =20 int split_folio_to_list(struct folio *folio, struct list_head *list) { - int ret =3D min_order_for_split(folio); - - if (ret < 0) - return ret; - - return split_huge_page_to_list_to_order(&folio->page, list, ret); + return split_huge_page_to_list_to_order(&folio->page, list, 0); } =20 /* diff --git a/mm/truncate.c b/mm/truncate.c index 91eb92a5ce4f..1c15149ae8e9 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -194,6 +194,7 @@ bool truncate_inode_partial_folio(struct folio *folio, = loff_t start, loff_t end) size_t size =3D folio_size(folio); unsigned int offset, length; struct page *split_at, *split_at2; + unsigned int min_order; =20 if (pos < start) offset =3D start - pos; @@ -223,8 +224,9 @@ bool truncate_inode_partial_folio(struct folio *folio, = loff_t start, loff_t end) if (!folio_test_large(folio)) return true; =20 + min_order =3D mapping_min_folio_order(folio->mapping); split_at =3D folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE); - if (!try_folio_split(folio, split_at, NULL)) { + if (!try_folio_split(folio, split_at, NULL, min_order)) { /* * try to split at offset + length to make sure folios within * the range can be dropped, especially to avoid memory waste @@ -254,7 +256,7 @@ bool truncate_inode_partial_folio(struct folio *folio, = loff_t start, loff_t end) */ if (folio_test_large(folio2) && folio2->mapping =3D=3D folio->mapping) - try_folio_split(folio2, split_at2, NULL); + try_folio_split(folio2, split_at2, NULL, min_order); =20 folio_unlock(folio2); out: --=20 2.51.0 From nobody Fri Dec 19 12:15:10 2025 Received: from SA9PR02CU001.outbound.protection.outlook.com (mail-southcentralusazon11013026.outbound.protection.outlook.com [40.93.196.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BB8152248B4; 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Received: from DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) by IA1PR12MB8222.namprd12.prod.outlook.com (2603:10b6:208:3f2::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9203.10; Fri, 10 Oct 2025 17:39:30 +0000 Received: from DS7PR12MB9473.namprd12.prod.outlook.com ([fe80::5189:ecec:d84a:133a]) by DS7PR12MB9473.namprd12.prod.outlook.com ([fe80::5189:ecec:d84a:133a%5]) with mapi id 15.20.9203.009; Fri, 10 Oct 2025 17:39:30 +0000 From: Zi Yan To: linmiaohe@huawei.com, david@redhat.com, jane.chu@oracle.com, kernel@pankajraghav.com, syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com Cc: ziy@nvidia.com, akpm@linux-foundation.org, mcgrof@kernel.org, nao.horiguchi@gmail.com, Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , "Matthew Wilcox (Oracle)" , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 2/2] mm/memory-failure: improve large block size folio handling. 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charset="utf-8" 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 Signed-off-by: Zi Yan Reviewed-by: Luis Chamberlain --- 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, s= truct 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; =20 lock_page(page); - ret =3D split_huge_page(page); + ret =3D split_huge_page_to_list_to_order(page, NULL, new_order); unlock_page(page); =20 if (ret && release) @@ -2280,6 +2281,7 @@ int memory_failure(unsigned long pfn, int flags) folio_unlock(folio); =20 if (folio_test_large(folio)) { + int new_order =3D 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 =3D page_folio(p); res =3D -EHWPOISON; kill_procs_now(p, pfn, flags, folio); put_page(p); @@ -2621,7 +2630,15 @@ static int soft_offline_in_use_page(struct page *pag= e) }; =20 if (!huge && folio_test_large(folio)) { - if (try_to_split_thp_page(page, true)) { + int new_order =3D 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; } --=20 2.51.0