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Tue, 10 Dec 2024 09:15:11 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id mc69KJ8GWGebLQAAD6G6ig (envelope-from ); Tue, 10 Dec 2024 09:15:11 +0000 Message-ID: Date: Tue, 10 Dec 2024 10:15:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/6] mm: move per-vma lock into vm_area_struct Content-Language: en-US To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: 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, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com References: <20241206225204.4008261-1-surenb@google.com> <20241206225204.4008261-3-surenb@google.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 56B05C0010 X-Stat-Signature: 5b6rxdtm531kzufuyrw15edfurgbp3ff X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1733822104-697906 X-HE-Meta: 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 T8dzjkU8 d0tX3wNgXeAZwnl1yL1rLLljFRIeNFIR/QqExt07K5UWlHpouYFvFzsqul5wUXo04w5oHrW+0YPJb/rII3qXouPiFqF401NjlASFY6YraHjmqLCcJ2uIeOyzPtOBnN/1vSv7WjTHEjhSlFF+P3STrhPZ7TlTbcz8PIg34VA+sHfzX4ONnI1n5oNGJcdbUAWaHZOxoyyyChR6iz9q7YNgBujHhJVWKmMryuwMmVMqI4u3CWnfXG4oVNzmuvkTTMvbAvke4m24Ith5cdVm4JOGiq4hGWQrOeAm7mLBEQHvQRP5Hx227kQ/4DH1jPuPyrgxkKf6OlHolf/eIOnWFQdIAb2KDGQNJG9svfnMjn3CHjRa3ZjVfSqcSuZtvFZXU5/hyCvyndjY6zPSRp8MxAh88OduZyP31yL6UKCKRWUsM6JcrydU= 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 12/6/24 23:51, 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 allows > vm_area_struct to use SLAB_TYPESAFE_BY_RCU later in this patchset. > Move vm_lock back into vm_area_struct, aligning it at the cacheline > boundary and changing the cache to be cacheline-aligned as well. > With kernel compiled using defconfig, this causes VMA memory consumption > to grow from 160 (vm_area_struct) + 40 (vm_lock) bytes to 256 bytes: > > slabinfo before: > ... : ... > vma_lock ... 40 102 1 : ... > vm_area_struct ... 160 51 2 : ... > > slabinfo after moving vm_lock: > ... : ... > vm_area_struct ... 256 32 2 : ... > > Aggregate VMA memory consumption per 1000 VMAs grows from 50 to 64 pages, > which is 5.5MB per 100000 VMAs. Note that the size of this structure is > dependent on the kernel configuration and typically the original size is > higher than 160 bytes. Therefore these calculations are close to the > worst case scenario. A more realistic vm_area_struct usage before this > change is: > > ... : ... > vma_lock ... 40 102 1 : ... > vm_area_struct ... 176 46 2 : ... > > Aggregate VMA memory consumption per 1000 VMAs grows from 54 to 64 pages, > which is 3.9MB per 100000 VMAs. > This memory consumption growth can be addressed later by optimizing the > vm_lock. > > [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/ > > Signed-off-by: Suren Baghdasaryan > Reviewed-by: Lorenzo Stoakes > Reviewed-by: Shakeel Butt Reviewed-by: Vlastimil Babka