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AJvYcCWGE3zgjoxPyClDG2Je1QAPA4A1XYEdxtsc/1JlKZutc7cKsXVDPH8ckFnkZjWlfuAF7Crma1r1hw==@kvack.org X-Gm-Message-State: AOJu0YyXGCLPOtVG64R+jZpHRshmbU828XcGfWzQgQSLynQkn/F+At4j pRIbMF+7PC82AyXeNuahtDs6ot5TAV8eJDOMgO8ZtzPn0xyvP/jSvqfLoB/f9OcQ7zH4Lbe8OxS a3M2R0s3W+O3tURAsCSXF6hnVk7QwuBOfyi6O X-Gm-Gg: ASbGnctxPnd4zM5+RJcKihBUkND1h9b2K5bMdoZnKDXKf4B0k3Mh8rJTk5MVkHX1cau SfQO9DumOXVuC5DBBDA9Up5UDSWVO18AI9Nw3VA== X-Google-Smtp-Source: AGHT+IFJyR0dDcxC/f6LHenxgewwrYv9Jx5mlAu1JXM0BBqE5F89/4BDPtKaTIDbqvtpXSYPm4Rn1RKJUXSvZp9ckNw= X-Received: by 2002:ac8:5ac5:0:b0:465:18f3:79cc with SMTP id d75a77b69052e-46c7cf3a0b0mr3738181cf.11.1736438251561; Thu, 09 Jan 2025 07:57:31 -0800 (PST) MIME-Version: 1.0 References: <20250109023025.2242447-1-surenb@google.com> <52ecd3fa-5978-4f4b-b969-c42b00a5b885@suse.cz> In-Reply-To: <52ecd3fa-5978-4f4b-b969-c42b00a5b885@suse.cz> From: Suren Baghdasaryan Date: Thu, 9 Jan 2025 07:57:20 -0800 X-Gm-Features: AbW1kvbZjINIYtb-WWp6pBAMqVSVltPTuNSh_0Yi2yz7niCtjZY4iye3-jfL8Fw Message-ID: Subject: Re: [PATCH v8 00/16] move per-vma lock into vm_area_struct To: Vlastimil Babka Cc: akpm@linux-foundation.org, peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D671A100007 X-Stat-Signature: 6ce915tx96ubwqyb4kjy5o9sskt1jaw1 X-Rspam-User: X-HE-Tag: 1736438252-897350 X-HE-Meta: U2FsdGVkX1+AI7rFzBegmwyZiOTNs4GpUMS2e1ULnJTIT2XxlmJAv59Rff29COfIBT0K/Fkrt4fumRslRtvlvL2xG+9vUjHgM75AFDfNhonpuvRx4UBlJnXYsiXGecfBm8KpX/SyLR7nm1bSEP5ggMCDQNMM1+cooJ143avQm2uD0Mdo2fEdkOfnvXsnuJmARtcUGJ4JoGZ/5J+LvcMwQoVfBa8ZCg9wRLQ7Z8wUA0xldz38zqBEa8NOilDf8ZnUSZFBiD1AatlaAP9cb5AWwP6joAiQJwcp+e7RoYRgByv1dxKIyyg3p/GoIUlmNhQvRUPc+RnxOPlR5ytBuSTk/rfIPYENlLo1jyAlbQgdLVDPCrTtUai2ApFV59aubRO2myToNJ9YP9crCDCHCFZ5LBfxCVUWIkBtC2fjMuoRjgYyYtRCq3N7W6vLeJI/Gak+G7TefzbFIzGS0qNpgMXVqVNH1QTDrvHv/MEFcRhlxXIGYhGjDFCalUv3fqf6I0HvfaA0r1tbzGe8/6Qwkc8INfmVfYkE+de6Z7A4UQdgPFYl7T48wElHihjx077XF1/TYKSNfjD6xbLzGdg5apOa5eTk51PIhnx10iqjq1Cgup+pldFuYqYA+mh/5kI+Pln04G4gm/h+MR5eP/Ry1e67ZD0GXb+mBU3+DBwAPESwuz9Uph1759iUsL6tgpNMqyBlMBN+9qPBICwpgtdUtRSQD61jxvZ0PDaAHQ+4DTMLJ1ek+NxS4mwGZB7/xk6+zUbFeTazkY4+hdLvFAPy8ed5iJUEDmObOZ66NLfotUwuf9ZhLmDlb0/zXI6iJz3jpBxhWu0cv8Vkec2f/3wgjcNr/r6MwpPubK3nGnroKnIsLfn1AHLzZni0C/8J27grp8rkUnzIQTTKRFrndV07ovKqyLphAQPG6/bS1GzGI9xbkzEGaPuf6S+IeOEfqIJy+InthvhTUrtLn/Xoi+9lQCy 80wFycj2 ABAFVgow9HJ+QED3hegMXiehzz0tJ4XUj5txbP1rr1FPtuOmc0wd9N/QcMmQu6/Lm7y5dV59NxtJaMrPiMSkjfuZvkBvqaGdUBLF93Rv6VxgSU6pjxFlaxVwyHkuOSSpoWm6Gcxw5jbZdYB5uORlXphd0ie6gTBxvfeHj6OqsPwRiYTmruPlQe5qa9qITsq+zNxnawOEA620lNcGAZF6EnLB7A49Z4oCbGZWl/EPWo9kXIT/J4UTqq7hJpU4y3QPSf8L7mQoKhNrvepSv3zECgv+PUnLyDW4EUFPAxc/pTXRmNPKpbJJFrwwef5M9HNHNYzycmKjsVUBnyhg88sWjho+mNguzy/EouQzwGlnCo2cMDOkdo4AWXHNE1tpcy468rSb/ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jan 9, 2025 at 5:40=E2=80=AFAM Vlastimil Babka wro= te: > > Btw the subject became rather incomplete given all the series does :) > > On 1/9/25 3:30 AM, Suren Baghdasaryan wrote: > > 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 allow= s > > 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 un= til > > it is inserted into vma tree; > > 3. replaces vm_lock and vma->detached flag with a reference counter; > > 4. changes vm_area_struct cache to SLAB_TYPESAFE_BY_RCU to allow for th= eir > > 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= %* > > Given how patch 2 discusses memory growth due to moving the lock, should > also patch 11 discuss how the replacement with refcount reduces the > memory footprint? And/or the cover letter could summarize the impact of > the whole series in that aspect? That's a good idea. I can amend the cover letter and the description of patch 11 to include size information. > Perhaps the refcount doesn't reduce > anything as it's smaller but sits alone in the cacheline? Could it be > grouped with some non-hot fields instead as a followup, so could we get > to <=3D192 (non-debug) size without impacting performance? Yes, absolutely. Before this series, vm_area_struct was roughly 168 bytes and vm_lock was 40 bytes. After the changes vm_area_struct becomes 256 bytes. I was planning to pack the fields as a follow-up patch similar to an earlier one [1] and bring the size of vm_area_struct to < 192. I felt this patchset already does many things and did not include it here but I can add it at the end of this patchset if you think it's essential. [1] https://lore.kernel.org/all/20241111205506.3404479-5-surenb@google.com/ > > > Changes since v7 [4]: > > - Removed additional parameter for vma_iter_store() and introduced > > vma_iter_store_attached() instead, per Vlastimil Babka and > > Liam R. Howlett > > - Fixed coding style nits, per Vlastimil Babka > > - Added Reviewed-bys and Acked-bys, per Vlastimil Babka > > - Added Reviewed-bys and Acked-bys, per Liam R. Howlett > > - Added Acked-by, per Davidlohr Bueso > > - Removed unnecessary patch changeing nommu.c > > - Folded a fixup patch [5] into the patch it was fixing > > - Changed calculation in __refcount_add_not_zero_limited() to avoid > > overflow, to change the limit to be inclusive and to use INT_MAX to > > indicate no limits, per Vlastimil Babka and Matthew Wilcox > > - Folded a fixup patch [6] into the patch it was fixing > > - Added vm_refcnt rules summary in the changelog, per Liam R. Howlett > > - Changed writers to not increment vm_refcnt and adjusted VMA_REF_LIMIT > > to not reserve one count for a writer, per Liam R. Howlett > > - Changed vma_refcount_put() to wake up writers only when the last read= er > > is leaving, per Liam R. Howlett > > - Fixed rwsem_acquire_read() parameters when read-locking a vma to matc= h > > the way down_read_trylock() does lockdep, per Vlastimil Babka > > - Folded vma_lockdep_init() into vma_lock_init() for simplicity > > - Brought back vma_copy() to keep vm_refcount at 0 during reuse, > > per Vlastimil Babka > > > > What I did not include in this patchset: > > - Liam's suggestion to change dump_vma() output since it's unclear to m= e > > how it should look like. The patch is for debug only and not critical f= or > > the rest of the series, we can change the output later or even drop it = if > > necessary. > > > > [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/20241226170710.1159679-1-surenb@google.= com/ > > [5] https://lore.kernel.org/all/20250107030415.721474-1-surenb@google.c= om/ > > [6] https://lore.kernel.org/all/20241226200335.1250078-1-surenb@google.= com/ > > > > Patchset applies over mm-unstable after reverting v7 > > (current SHA range: 588f0086398e - fb2270654630) > > > > Suren Baghdasaryan (16): > > 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: introduce __refcount_{add|inc}_not_zero_limited > > mm: replace vm_lock and detached flag with a reference count > > 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/mm/process_addrs.rst | 44 +++++---- > > include/linux/mm.h | 152 ++++++++++++++++++++++------- > > include/linux/mm_types.h | 36 ++++--- > > include/linux/mmap_lock.h | 6 -- > > include/linux/rcuwait.h | 13 +-- > > include/linux/refcount.h | 20 +++- > > include/linux/slab.h | 6 -- > > include/linux/types.h | 12 +++ > > kernel/fork.c | 128 +++++++++++------------- > > mm/debug.c | 12 +++ > > mm/init-mm.c | 1 + > > mm/memory.c | 94 +++++++++++++++--- > > mm/mmap.c | 3 +- > > mm/userfaultfd.c | 32 +++--- > > mm/vma.c | 23 ++--- > > mm/vma.h | 15 ++- > > tools/testing/vma/linux/atomic.h | 5 + > > tools/testing/vma/vma_internal.h | 93 ++++++++---------- > > 18 files changed, 435 insertions(+), 260 deletions(-) > > >