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 170B07DA66 for ; Tue, 15 Sep 2026 00:45:13 +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=1789433116; cv=none; b=SeVWQUUQzWCBvXbbwmpjZEC8u2rtSsgrIcwBuE/9Kvqc8swPkDbpos+GDHPhsLQllP54e7ruSmiQecimMQu0dlYCkHlXN9kTjmV+C9IFWS5wNiG/b1dyWLVRnd8Y7INdigLLXHdC8ZFAe9O2hMJJhOdP18ttdvUyD8WzRm54T6k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789433116; c=relaxed/simple; bh=uUjZc5OdMfvO1MaONUqHqnm7+zrbs+M2EQ0cACi78Ws=; h=Date:To:From:Subject:Message-Id; b=RlgJZ/H+s0uwr7XzpXhJngTOlbi2PbRvA3Z/c9tVGIWxptQ3+iRaBCHdDn42FC4oxXOF2Hmfs7jsKaThOlRpLYfRjiHiSqy6CER4p8DohNtMRK66k/cVOkpTYKFO3qsE2dqElk9aTk+zH0uhMpmsSMaZUgW5n9nz1NGWBsbSRBc= 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=iS+COEfZ; 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="iS+COEfZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19F2A1F00899; Tue, 15 Sep 2026 00:45:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789433113; bh=AaZfqYA7nWtFd/vCMQAAfUzCLNhaVumlNdqj3yl69UU=; h=Date:To:From:Subject; b=iS+COEfZ6mtQxByjoKe9l+aBYjk/S4AC+/dfOFopsaZ4yK8CjsBtjzFVT8shG6ZQt meiw1Jf5MdDS1tBwB9PVnfxv6uBp/rPnZSVtJEADuG78yo2Rc1it0WmYLXY+Iws4nN Vg/00GY+YgyV85LnKckUx0qWxwzQCh59Ue1+JKvQ= Date: Mon, 14 Sep 2026 17:45:12 -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-new branch Message-Id: <20260915004513.19F2A1F00899@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-new 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-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next 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: Tue, 15 Sep 2026 01:14:51 +0800 The check only exists to avoid the expensive PMD-splitting unmap of a folio that cannot be split anyway. Move it from __folio_split() into unmap_folio(), right before the PMD split, so both the anon and file split helpers get the 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/20260915-swap-thp-cleanup-v5-10-39878b37dfb0@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 Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Chris Li Cc: David Hildenbrand (Arm) Cc: Dev Jain Cc: Kemeng Shi Cc: Lance Yang Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Nhat Pham Cc: Ryan Roberts Cc: Suren Baghdasaryan Cc: Vlastimil Babka --- mm/huge_memory.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) --- a/mm/huge_memory.c~mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio +++ a/mm/huge_memory.c @@ -3539,13 +3539,17 @@ void vma_adjust_trans_huge(struct vm_are split_huge_pmd_if_needed(next, end); } -static void unmap_folio(struct folio *folio) +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; @@ -3560,6 +3564,8 @@ 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, @@ -4030,7 +4036,9 @@ 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(); @@ -4124,7 +4132,9 @@ 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); @@ -4332,15 +4342,6 @@ 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); @@ -4379,7 +4380,6 @@ 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); @@ -4427,9 +4427,6 @@ 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