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Thu, 20 Jun 2024 17:35:47 -0700 (PDT) Received: from [2620:0:1008:15:e2ae:cbae:96cc:d4e8] ([2620:0:1008:15:e2ae:cbae:96cc:d4e8]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2c709e9f0aasm2290798a91.0.2024.06.20.17.35.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Jun 2024 17:35:46 -0700 (PDT) Date: Thu, 20 Jun 2024 17:35:45 -0700 (PDT) From: David Rientjes To: Andrew Morton , "Liam R. Howlett" , Suren Baghdasaryan , Matthew Wilcox , Christoph Lameter , "Paul E. McKenney" , Tejun Heo , Johannes Weiner , Davidlohr Bueso cc: Namhyung Kim , linux-mm@kvack.org Subject: MM global locks as core counts quadruple Message-ID: <07e7d078-0c9d-6a1f-1ab5-295f86974b72@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 0B23E2000E X-Stat-Signature: xtyozwy3b6jkkt7x8az4tt4pgkwr99bw X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1718930148-622442 X-HE-Meta: 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 KS66ricQ cvI6R4hT8YJdY5Sw5++0waUto6goM7FSorWQy1XXq6VpQglsS61evIBqny2qJAwKNBTzgKkpI0J5qyP+3BjPfRK/AP2gz/2iRdNJf/r3uTXMoa5tsck9Lx4IgNVpvxMCxCSkSdMA00TqEurjxy2iWE1zaaFETnspn1oj7ynaQJDUrtZfaRVKAwusH3QA+mY8w326Kd/FU3Rf6QRUn1avyWbsLcDTe3r8ztLWZaxRZ5aXHrVEY7Zr5+lF6+nDyh/F/rX1cEaNjVPoqdAE5ojjQ1NqsrhJBzIwwmokyb6nIOtORzjiwLkYDM0DHeAffWAQv5AGn5EcTS6v2ncJYRNMXDu+6sw== 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: Hi all, As core counts are rapidly expanding over the next four years, Namhyung and I were looking at global locks that we're already seeing high contention on even today. Some of these are not MM specific: - cgroup_mutex - cgroup_threadgroup_rwsem - tasklist_lock - kernfs_mutex (although should now be substantially better with the kernfs_locks array) Others *are* MM specific: - list_lrus_mutex - pcpu_drain_mutex - shrinker_mutex (formerly shrinker_rwsem) - vmap_purge_lock - slab_mutex This is only looking at fleet data for global static locks, not locks like zone->lock that get dynamically allocated. (mmap_lock was substantially improved by per-vma locking, although does show up for very large vmas.) Couple questions: (1) How are people quantifying these pain points, if at all, in synthetic testing? Any workloads or benchmarks that are really good at doing this in the lab beyond the traditional will-it-scale? (The above is from production data.) (2) Is anybody working on any of the above global locks? Trying to surface gaps for locks that will likely become even more painful in the coming years. Thanks!