From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7CB024D8D1 for ; Sat, 7 Dec 2024 04:29:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733545765; cv=none; b=kIuFABXBYdyTOvY2N9OLbX/wUA2bSOnOFHnyPD/OtJ0VMe0hCotgfI9K8WJ+tfAjvjYTOOlRKemLDl7VRAPPP1l0B1d10TNtEBDb3K/25CXDfdq4vayv5zhhRcn8snhXLViv3Mo3vzA59ICyVlaCmSN/n5rv4mto5yHOL2XVW6c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733545765; c=relaxed/simple; bh=IA8qJMevyqUxWmzGDtQBVMjrjYbeY6pg0a3ihmZRE/w=; h=Date:To:From:Subject:Message-Id; b=E7wyP0MdcXMGKN4lwmelTbfApQ97S+S7jB5QjvUoFfL1zNO8inmSrGYqpiDDgF26CBh+McDMBAXwiVkvPwZ431DtvibdnW8dGDRjYJ0f6VRQ6OqOn8LUvnnv3w+ZMUGWUptjFoeW36nhpAg7vxz4vzKJbm0IG4N0Wlwqxaeu44M= 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=CF2pcgNZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="CF2pcgNZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 04F8BC4CECD; Sat, 7 Dec 2024 04:29:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1733545765; bh=IA8qJMevyqUxWmzGDtQBVMjrjYbeY6pg0a3ihmZRE/w=; h=Date:To:From:Subject:From; b=CF2pcgNZK8vLWzHAurujIGPtRzLF62J7/jIvqr7HNV66ZpMsGmsPPXHzI5qZwQgic Y8f5cPZbb7TxgxyIJtyyl/wxnuBC4beeFL4V2Wh0bpQxfsb9PmPTa6ezcK/3cdtaWp oR0wj8hqACphGTzWiogp4HRCDfau81/Y3tf0RTio= Date: Fri, 06 Dec 2024 20:29:24 -0800 To: mm-commits@vger.kernel.org,willy@infradead.org,vbabka@suse.cz,souravpanda@google.com,shakeel.butt@linux.dev,richard.weiyang@gmail.com,peterz@infradead.org,peterx@redhat.com,paulmck@kernel.org,pasha.tatashin@soleen.com,oleg@redhat.com,mjguzik@gmail.com,minchan@google.com,mhocko@suse.com,mgorman@techsingularity.net,lorenzo.stoakes@oracle.com,Liam.Howlett@Oracle.com,jannh@google.com,hughd@google.com,hdanton@sina.com,hannes@cmpxchg.org,dhowells@redhat.com,david@redhat.com,dave@stgolabs.net,corbet@lwn.net,brauner@kernel.org,surenb@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-introduce-vma_start_read_locked_nested-helpers.patch added to mm-unstable branch Message-Id: <20241207042925.04F8BC4CECD@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: introduce vma_start_read_locked{_nested} helpers has been added to the -mm mm-unstable branch. Its filename is mm-introduce-vma_start_read_locked_nested-helpers.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-introduce-vma_start_read_locked_nested-helpers.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 the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Suren Baghdasaryan Subject: mm: introduce vma_start_read_locked{_nested} helpers Date: Fri, 6 Dec 2024 14:51:58 -0800 Patch series "move per-vma lock into vm_area_struct", v5. Back when per-vma locks were introduced, vm_lock was moved out of vm_area_struct in [1] because of the performance regression caused by false cacheline sharing. Recent investigation [2] revealed that the regressions is limited to a rather old Broadwell microarchitecture and even there it can be mitigated by disabling adjacent cacheline prefetching, see [3]. Splitting single logical structure into multiple ones leads to more complicated management, extra pointer dereferences and overall less maintainable code. When that split-away part is a lock, it complicates things even further. With no performance benefits, there are no reasons for this split. Merging the vm_lock back into vm_area_struct also allows vm_area_struct to use SLAB_TYPESAFE_BY_RCU later in this patchset. This patchset: 1. moves vm_lock back into vm_area_struct, aligning it at the cacheline boundary and changing the cache to be cacheline-aligned to minimize cacheline sharing; 2. changes vm_area_struct initialization to mark new vma as detached until it is inserted into vma tree; 3. changes vm_area_struct cache to SLAB_TYPESAFE_BY_RCU to allow for their reuse and to minimize call_rcu() calls. To avoid bloating vm_area_struct, we introduce unioned freeptr_t field and allow freeptr_offset to be used with ctor in a separate patch. Pagefault microbenchmarks do not show noticeable performance change. [1] https://lore.kernel.org/all/20230227173632.3292573-34-surenb@google.com/ [2] https://lore.kernel.org/all/ZsQyI%2F087V34JoIt@xsang-OptiPlex-9020/ [3] https://lore.kernel.org/all/CAJuCfpEisU8Lfe96AYJDZ+OM4NoPmnw9bP53cT_kbfP_pR+-2g@mail.gmail.com/ This patch (of 6): Introduce helper functions which can be used to read-lock a VMA when holding mmap_lock for read. Replace direct accesses to vma->vm_lock with these new helpers. Link: https://lkml.kernel.org/r/20241206225204.4008261-1-surenb@google.com Link: https://lkml.kernel.org/r/20241206225204.4008261-2-surenb@google.com Signed-off-by: Suren Baghdasaryan Reviewed-by: Lorenzo Stoakes Reviewed-by: Davidlohr Bueso Reviewed-by: Shakeel Butt Cc: Christian Brauner Cc: David Hildenbrand Cc: David Howells says: Cc: Hillf Danton Cc: Hugh Dickins Cc: Jann Horn Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Liam R. Howlett Cc: Mateusz Guzik Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Cc: Minchan Kim Cc: Oleg Nesterov Cc: Pasha Tatashin Cc: Paul E. McKenney Cc: Peter Xu Cc: Sourav Panda Cc: Vlastimil Babka Cc: Peter Zijlstra Cc: Wei Yang Signed-off-by: Andrew Morton --- include/linux/mm.h | 24 ++++++++++++++++++++++++ mm/userfaultfd.c | 22 +++++----------------- 2 files changed, 29 insertions(+), 17 deletions(-) --- a/include/linux/mm.h~mm-introduce-vma_start_read_locked_nested-helpers +++ a/include/linux/mm.h @@ -734,6 +734,30 @@ static inline bool vma_start_read(struct return true; } +/* + * Use only while holding mmap read lock which guarantees that locking will not + * fail (nobody can concurrently write-lock the vma). vma_start_read() should + * not be used in such cases because it might fail due to mm_lock_seq overflow. + * This functionality is used to obtain vma read lock and drop the mmap read lock. + */ +static inline void vma_start_read_locked_nested(struct vm_area_struct *vma, int subclass) +{ + mmap_assert_locked(vma->vm_mm); + down_read_nested(&vma->vm_lock->lock, subclass); +} + +/* + * Use only while holding mmap read lock which guarantees that locking will not + * fail (nobody can concurrently write-lock the vma). vma_start_read() should + * not be used in such cases because it might fail due to mm_lock_seq overflow. + * This functionality is used to obtain vma read lock and drop the mmap read lock. + */ +static inline void vma_start_read_locked(struct vm_area_struct *vma) +{ + mmap_assert_locked(vma->vm_mm); + down_read(&vma->vm_lock->lock); +} + static inline void vma_end_read(struct vm_area_struct *vma) { rcu_read_lock(); /* keeps vma alive till the end of up_read */ --- a/mm/userfaultfd.c~mm-introduce-vma_start_read_locked_nested-helpers +++ a/mm/userfaultfd.c @@ -84,16 +84,8 @@ static struct vm_area_struct *uffd_lock_ mmap_read_lock(mm); vma = find_vma_and_prepare_anon(mm, address); - if (!IS_ERR(vma)) { - /* - * We cannot use vma_start_read() as it may fail due to - * false locked (see comment in vma_start_read()). We - * can avoid that by directly locking vm_lock under - * mmap_lock, which guarantees that nobody can lock the - * vma for write (vma_start_write()) under us. - */ - down_read(&vma->vm_lock->lock); - } + if (!IS_ERR(vma)) + vma_start_read_locked(vma); mmap_read_unlock(mm); return vma; @@ -1491,14 +1483,10 @@ static int uffd_move_lock(struct mm_stru mmap_read_lock(mm); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (!err) { - /* - * See comment in uffd_lock_vma() as to why not using - * vma_start_read() here. - */ - down_read(&(*dst_vmap)->vm_lock->lock); + vma_start_read_locked(*dst_vmap); if (*dst_vmap != *src_vmap) - down_read_nested(&(*src_vmap)->vm_lock->lock, - SINGLE_DEPTH_NESTING); + vma_start_read_locked_nested(*src_vmap, + SINGLE_DEPTH_NESTING); } mmap_read_unlock(mm); return err; _ Patches currently in -mm which might be from surenb@google.com are alloc_tag-fix-module-allocation-tags-populated-area-calculation.patch alloc_tag-fix-set_codetag_empty-when-config_mem_alloc_profiling_debug.patch seqlock-add-raw_seqcount_try_begin.patch mm-convert-mm_lock_seq-to-a-proper-seqcount.patch mm-introduce-mmap_lock_speculate_try_beginretry.patch mm-introduce-vma_start_read_locked_nested-helpers.patch mm-move-per-vma-lock-into-vm_area_struct.patch mm-mark-vma-as-detached-until-its-added-into-vma-tree.patch mm-make-vma-cache-slab_typesafe_by_rcu.patch mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch docs-mm-document-latest-changes-to-vm_lock.patch