From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 74C9D46AA6E for ; Wed, 23 Sep 2026 22:32:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790202764; cv=none; b=DpLLMgOZ4kW8D08RzlGitCgxWVNXhOtDIx89ULCm6tDXhCSY58B+MiPzgcpOXcfQ3PXtbglurlGYpmUoyC3TEIpQUzrb2eRu6iszdof5Uz62HQjCBa3tLa1DZbmVHpqow2zhkodv0JEOjTZybor4nF51r0BKHVhRYMxz8/X8+KA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790202764; c=relaxed/simple; bh=Usg75MALIgq8vAyGIN9m8/FkR1bOhhkihftjiHSqkgk=; h=Date:To:From:Subject:Message-Id; b=ICAP4STG9jyeTGPt4DrLxHA2rpXmAN/yQqYI79JMFXdtdJY3dEVIQQOoESuNGi62ndqsDpN1Oj10au4/0jmvCJ+QaLEwVD/i3XTx17fMXNVSebC4iziXLJ7fbSCoaPL7AZzcE81VVqHDIARpXumZH9MHTkd1jk3eYMi1MveQzrQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=z1uGYXxx; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="z1uGYXxx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 497891F00893; Wed, 23 Sep 2026 22:32:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790202762; bh=YQzHD+01/msDdRi6+HQ1wkbPBUqDj2z4c5iikl5U0dU=; h=Date:To:From:Subject; b=z1uGYXxx+V1pU5kCK74hZoaAcN752odcQBn5Ga1E3M2FWg/kxGVMVmQtS2SMF71Co nSW39gAnxi3PPlSRxJPTo7FpY/Kgy+E4BEtUoI+YgJewnhX2U1liY8KMmFoR/4B0uC H0SL7PBSMvDkCGTSoSu+0n6v1oVh4HmNN2QiYX38= Date: Wed, 23 Sep 2026 15:32:41 -0700 To: mm-commits@vger.kernel.org,kasong@tencent.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio.patch added to mm-unstable branch Message-Id: <20260923223242.497891F00893@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/huge_memory: move the racy refcount check into unmap_folio() has been added to the -mm mm-unstable branch. Its filename is mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Kairui Song Subject: mm/huge_memory: move the racy refcount check into unmap_folio() Date: Wed, 23 Sep 2026 23:32:41 +0200 The check only exists to avoid the expensive PMD-splitting unmap of a folio that cannot be split anyway. Move it from __folio_split() and folio_split_unmapped() into one check in unmap_folio(), right before the PMD split. All split helpers get the same early check without repeating it. unmap_folio() now returns -EAGAIN if the check fails and the split helpers propagate the error. folio_split_unmapped() drops its own copy of the check: it works on already unmapped folios and the definitive folio_ref_freeze() in __folio_freeze_split_anon() still catches unexpected references. Link: https://lore.kernel.org/20260923-swap-thp-cleanup-v6-10-ba1b4ba72c6f@tencent.com Signed-off-by: Kairui Song Signed-off-by: Andrew Morton Reviewed-by: Zi Yan Reviewed-by: Kiryl Shutsemau (Meta) Reviewed-by: Yeoreum Yun Acked-by: David Hildenbrand (Arm) Cc: Lorenzo Stoakes Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Lance Yang Cc: Usama Arif Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Chris Li Cc: Kemeng Shi Cc: Nhat Pham Cc: Baoquan He Cc: Barry Song Cc: Youngjun Park Cc: Shivam Kalra Cc: Kairui Song --- mm/huge_memory.c | 34 ++++++++++++++++++---------------- 1 file changed, 18 insertions(+), 16 deletions(-) --- a/mm/huge_memory.c~mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio +++ a/mm/huge_memory.c @@ -3538,13 +3538,22 @@ void vma_adjust_trans_huge(struct vm_are split_huge_pmd_if_needed(next, end); } -static void unmap_folio(struct folio *folio) +/* + * A return value of 0 does not mean that unmapping succeeded. It might + * still have failed, but remap_anon_folio() must be called afterwards, + * for anon folios. + */ +static int unmap_folio(struct folio *folio) { enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC | TTU_BATCH_FLUSH; VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); + /* Racy check if we can split the page, before we split PMDs */ + if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1) + return -EAGAIN; + if (folio_test_pmd_mappable(folio)) ttu_flags |= TTU_SPLIT_HUGE_PMD; @@ -3558,6 +3567,8 @@ static void unmap_folio(struct folio *fo try_to_unmap(folio, ttu_flags | TTU_IGNORE_MLOCK); try_to_unmap_flush(); + + return 0; } static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, @@ -4028,7 +4039,9 @@ static int __folio_freeze_split_anon(str if (folio_mapped(folio)) { need_remap = true; - unmap_folio(folio); + ret = unmap_folio(folio); + if (ret) + return ret; } local_irq_disable(); @@ -4122,7 +4135,9 @@ static int __folio_freeze_split_file(str if (shmem_mapping(mapping)) end = shmem_fallocend(mapping->host, end); - unmap_folio(folio); + ret = unmap_folio(folio); + if (ret) + return ret; xas_lock_irq(xas); @@ -4326,15 +4341,6 @@ static int __folio_split(struct folio *f i_mmap_lock_read(mapping); } - /* - * Racy check if we can split the page, before unmap_folio() will - * split PMDs - */ - if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1) { - ret = -EAGAIN; - goto out_unlock; - } - if (is_anon) ret = __folio_freeze_split_anon(folio, new_order, split_at, true, list, split_type); @@ -4373,7 +4379,6 @@ static int __folio_split(struct folio *f free_folio_and_swap_cache(new_folio); } -out_unlock: if (anon_vma) { anon_vma_unlock_write(anon_vma); put_anon_vma(anon_vma); @@ -4421,9 +4426,6 @@ int folio_split_unmapped(struct folio *f VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio); VM_WARN_ON_ONCE_FOLIO(!folio_test_anon(folio), folio); - if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1) - return -EAGAIN; - return __folio_freeze_split_anon(folio, new_order, &folio->page, false, NULL, SPLIT_TYPE_UNIFORM); } _ Patches currently in -mm which might be from kasong@tencent.com are mm-memcontrol-move-the-lru_zone_size-sanity-check-to-the-reader-side.patch mm-mglru-introduce-helpers-for-manipulating-gen-and-refs-flags.patch mm-migrate-copy-all-referenced-state-via-folio_migrate_lru_refs.patch mm-mglru-move-max_seq-read-into-walk_update_folio.patch mm-mglru-use-explicit-tier-range-in-read_ctrl_pos.patch mm-mglru-fix-potential-generation-folio-number-leak.patch mm-swap-fix-off-by-one-in-swap-cache-replace-sanity-check.patch mm-huge_memory-fix-rejection-of-swap-cache-folios-with-a-mapping.patch mm-huge_memory-invert-folio_ref_freeze-check-to-reduce-indentation.patch mm-huge_memory-split-the-routine-for-splitting-anon-and-file-folio.patch mm-huge_memory-rename-__split_unmapped_folio-to-__split_frozen_folio.patch mm-huge_memory-consolidate-irq-and-locking-for-folio-split.patch mm-huge_memory-move-eof-trimming-into-the-file-split-helper.patch mm-huge_memory-move-unmap-and-remap-into-the-split-helpers.patch mm-huge_memory-rename-remap_page-to-remap_anon_folio.patch mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio.patch mm-huge_memory-move-filemap-management-into-the-file-split-helper.patch mm-huge_memory-move-anon_vma-handling-into-the-anon-split-helper.patch mm-huge_memory-move-memcg-switch-into-the-file-split-helper.patch mm-huge_memory-drop-the-unused-do_lru-argument-of-the-file-split-helper.patch mm-huge_memory-clean-up-after-split-folio-freeing-in-__folio_split.patch mm-huge_memory-count-only-swap-cache-refs-in-anon-folio-split.patch mm-huge_memory-drop-the-redundant-mapping-argument-of-__split_frozen_folio.patch