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AJvYcCUZCfMnNJqH+utk6onHPvPvDU//dcUwAtYTj8M1XtFV6RqAC3Hbs8b/7HFaGdd42BwY2IoO9rUM0Zw=@vger.kernel.org X-Gm-Message-State: AOJu0Yz1PMQmKAEZbuZuQKNSn7ormXCj0SptTtZql2j+xCMK7qrYkr/0 y/UuMF2QjjA8ZE8Q92M/YnwnmPTwoetCIU6ixf8IERSLIBYiBU8korqLmRPiECBxZkNH9NbgYMW EeQ== X-Google-Smtp-Source: AGHT+IFqU1mAmYOjarqaEBcrctfJ39DVCGZvcnhZHusudh7jNm8NK23hT9sU/SxfoGJNKCasg65TO0nhtlQ= X-Received: from oabpu8.prod.google.com ([2002:a05:6870:9e88:b0:294:c73f:1037]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6871:67c2:b0:2bc:7c3d:18d8 with SMTP id 586e51a60fabf-2bc7c3d685cmr120712fac.33.1739486819281; Thu, 13 Feb 2025 14:46:59 -0800 (PST) Date: Thu, 13 Feb 2025 14:46:37 -0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog Message-ID: <20250213224655.1680278-1-surenb@google.com> Subject: [PATCH v10 00/18] reimplement per-vma lock as a refcount From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, david.laight.linux@gmail.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, richard.weiyang@gmail.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com Content-Type: text/plain; charset="UTF-8" Back when per-vma locks were introduces, 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. replaces vm_lock and vma->detached flag with a reference counter; 4. regroups vm_area_struct members to fit them into 3 cachelines; 5. changes vm_area_struct cache to SLAB_TYPESAFE_BY_RCU to allow for their reuse and to minimize call_rcu() calls. Pagefault microbenchmarks show performance improvement: Hmean faults/cpu-1 507926.5547 ( 0.00%) 506519.3692 * -0.28%* Hmean faults/cpu-4 479119.7051 ( 0.00%) 481333.6802 * 0.46%* Hmean faults/cpu-7 452880.2961 ( 0.00%) 455845.6211 * 0.65%* Hmean faults/cpu-12 347639.1021 ( 0.00%) 352004.2254 * 1.26%* Hmean faults/cpu-21 200061.2238 ( 0.00%) 229597.0317 * 14.76%* Hmean faults/cpu-30 145251.2001 ( 0.00%) 164202.5067 * 13.05%* Hmean faults/cpu-48 106848.4434 ( 0.00%) 120641.5504 * 12.91%* Hmean faults/cpu-56 92472.3835 ( 0.00%) 103464.7916 * 11.89%* Hmean faults/sec-1 507566.1468 ( 0.00%) 506139.0811 * -0.28%* Hmean faults/sec-4 1880478.2402 ( 0.00%) 1886795.6329 * 0.34%* Hmean faults/sec-7 3106394.3438 ( 0.00%) 3140550.7485 * 1.10%* Hmean faults/sec-12 4061358.4795 ( 0.00%) 4112477.0206 * 1.26%* Hmean faults/sec-21 3988619.1169 ( 0.00%) 4577747.1436 * 14.77%* Hmean faults/sec-30 3909839.5449 ( 0.00%) 4311052.2787 * 10.26%* Hmean faults/sec-48 4761108.4691 ( 0.00%) 5283790.5026 * 10.98%* Hmean faults/sec-56 4885561.4590 ( 0.00%) 5415839.4045 * 10.85%* Changes since v9 [4]: PATCH [4/18] - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() in vma_assert_{attached|detached}, per Lorenzo Stoakes - Rename vma_iter_store() into vma_iter_store_new(), per Lorenzo Stoakes - Expand changelog, per Lorenzo Stoakes - Update vma tests to check for vma detached state correctness, per Lorenzo Stoakes PATCH [5/18] - Add Reviewed-by, per Lorenzo Stoakes PATCH [6/18] - Add Acked-by, per Lorenzo Stoakes PATCH [7/18] - Refactor the code, per Lorenzo Stoakes - Remove Vlastimil's Acked-by since code is changed PATCH [8/18] - Drop inline for mmap_init_lock(), per Lorenzo Stoakes - Add Reviewed-by, per Lorenzo Stoakes PATCH [9/18] - Add Reviewed-by, per Lorenzo Stoakes PATCH [10/18] - New patch to add refcount_add_not_zero_acquire/refcount_set_release - Add Acked-by #slab, per Vlastimil Babka PATCH [11/18] - Change refcount limit to be used with xxx_acquire functions PATCH [12/18] - Use __refcount_inc_not_zero_limited_acquire() in vma_start_read(), per Hillf Danton - Refactor vma_assert_locked() to avoid vm_refcnt read when CONFIG_DEBUG_VM=n, per Mateusz Guzik - Update changelog, per Wei Yang - Change vma_start_read() to return EAGAIN if vma got isolated and changed lock_vma_under_rcu() back to detect this condition, per Wei Yang - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() when checking vma detached state, per Lorenzo Stoakes - Remove Vlastimil's Reviewed-by since code is changed PATCH [13/18] - Update vm_area_struct for tests, per Lorenzo Stoakes - Add Reviewed-by, per Lorenzo Stoakes PATCH [14/18] - Minimized duplicate code, per Lorenzo Stoakes PATCH [15/18] - Add Reviewed-by, per Lorenzo Stoakes PATCH [17/18] - Use refcount_set_release() in vma_mark_attached(), per Will Deacon PATCH [18/18] - Updated documenation, per Lorenzo Stoakes - Add Reviewed-by, per Lorenzo Stoakes [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/ [4] https://lore.kernel.org/all/20250111042604.3230628-1-surenb@google.com/ Patchset applies over mm-unstable Suren Baghdasaryan (18): mm: introduce vma_start_read_locked{_nested} helpers mm: move per-vma lock into vm_area_struct mm: mark vma as detached until it's added into vma tree mm: introduce vma_iter_store_attached() to use with attached vmas mm: mark vmas detached upon exit types: move struct rcuwait into types.h mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail mm: move mmap_init_lock() out of the header file mm: uninline the main body of vma_start_write() refcount: provide ops for cases when object's memory can be reused refcount: introduce __refcount_{add|inc}_not_zero_limited_acquire mm: replace vm_lock and detached flag with a reference count mm: move lesser used vma_area_struct members into the last cacheline mm/debug: print vm_refcnt state when dumping the vma mm: remove extra vma_numab_state_init() call mm: prepare lock_vma_under_rcu() for vma reuse possibility mm: make vma cache SLAB_TYPESAFE_BY_RCU docs/mm: document latest changes to vm_lock Documentation/RCU/whatisRCU.rst | 10 + Documentation/core-api/refcount-vs-atomic.rst | 37 +++- Documentation/mm/process_addrs.rst | 44 +++-- include/linux/mm.h | 176 ++++++++++++++---- include/linux/mm_types.h | 75 ++++---- include/linux/mmap_lock.h | 6 - include/linux/rcuwait.h | 13 +- include/linux/refcount.h | 125 +++++++++++++ include/linux/slab.h | 15 +- include/linux/types.h | 12 ++ kernel/fork.c | 129 ++++++------- mm/debug.c | 6 + mm/init-mm.c | 1 + mm/memory.c | 106 ++++++++++- mm/mmap.c | 3 +- mm/nommu.c | 4 +- mm/userfaultfd.c | 38 ++-- mm/vma.c | 27 ++- mm/vma.h | 15 +- tools/include/linux/refcount.h | 5 + tools/testing/vma/linux/atomic.h | 6 + tools/testing/vma/vma.c | 42 ++++- tools/testing/vma/vma_internal.h | 127 ++++++------- 23 files changed, 702 insertions(+), 320 deletions(-) base-commit: 47aa60e930fe7fc2a945e4406e3ad1dfa73bb47c -- 2.48.1.601.g30ceb7b040-goog