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[209.85.208.176]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-536870a45aesm1878409e87.183.2024.09.19.07.21.53 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Sep 2024 07:21:55 -0700 (PDT) Received: by mail-lj1-f176.google.com with SMTP id 38308e7fff4ca-2f029e9c9cfso10521321fa.2 for ; Thu, 19 Sep 2024 07:21:53 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCX2TnvNHrRQqqUb2oG26PvQGccv4sEN2/GiU2p3PKBQwSnpONFNNn/yRFDY/c+3ooYOA4blVFw/ow==@kvack.org X-Received: by 2002:a05:651c:543:b0:2ef:17ee:62a2 with SMTP id 38308e7fff4ca-2f791906358mr165636051fa.14.1726755713557; Thu, 19 Sep 2024 07:21:53 -0700 (PDT) MIME-Version: 1.0 References: <20240917143402.930114-1-boqun.feng@gmail.com> In-Reply-To: From: Linus Torvalds Date: Thu, 19 Sep 2024 16:21:36 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 0/4] Add hazard pointers to kernel To: Christoph Hellwig Cc: Boqun Feng , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@vger.kernel.org, "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Mark Rutland , Thomas Gleixner , Kent Overstreet , Vlastimil Babka , maged.michael@gmail.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: ED358A0004 X-Rspamd-Server: rspam01 X-Stat-Signature: ncdtfssdrq4aqobioymooj9qgf6nt7bp X-HE-Tag: 1726755718-809802 X-HE-Meta: U2FsdGVkX19t2rTlVfn7QTno49G8hq3GmVNXHaqJ+Hx1LQn74Np1zNKRGtQNOFaf39sXx1NaGnDIyduK0jZnoIWrw9RG4+zx17QPiHMEgbC3d5rnhCeuUfEv2oagW5ukwq9q3H2TFAofFnji94/aEglQgExBrB5TRu1oaFKUkvxaelU6Axz6Esn6lrw4RBiqEVbM9JlII0aXeaA9PUE825xUAySowGlXzCm1AnBw05GKv3T7HCLCNCQ4jIPR5doyGOaZiNDcJV2zv52vsM4S357rYTQ/Fum/vSYp7fZDh3Ik4Gh3qtNm2pg1P5iBsFHKaW6o3/ytjTwvt3xXFoRQKHiBSUHG4Tvy+TvDRHbVzYOVEdXzrFjfMN0qZoHIu/K8/1qiQBNaNEUgH+eqduijp8zCW4q5m1o2fT0Vy5CAt5WMQdzru/UVVEDqQciRjpPBNwT0vlA4n9cuhnYX49OLBfWZTTi1243/47Zd8aBZxEfmsA6kgxRGhK+ktR1IP6U+Mtmi1sZH5H7hWumRnbWa9SSVVUFcZ0ai0K0yjKPVXZK8xqfZf0UzPbml0cuUCImYFKLL8M7AZZO45VKo4APwy7JXbr/wiYAW+llC6UgiCbCfqF5yPnzZvSthb6K7R91DQnsWW7LjMnLInJ5PDcOmUU3w9IMTIxGiP8sRvtrlRfHC8XEvQKfY5Us78rkNw6Y0j+YshWUCZB7gSYKbMJGFQ/oGm564ObQcxdXUTpgUs3G5SL6cymP6xbSrZ/KpWt1eBDDb8nOQp6K1TigULJ8ant5OusPff8GGidzTc6dTrRtKuSveKoUT+QNkOYK/k7kp3pO2Fyir3DLR8GtNqme9+4OAbIVkHvdg82RbiW1Rg9dqlmD+EBxmuI4N+2uZtnHNgLub6SE9D13fchHjrvEJvS5LSytV0qzvqSXFKANPKuFT46H2Nu/fL0OFeErOfeV2HjvlTqf8Da/5wr0y2BS u7Mztplj 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 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, 19 Sept 2024 at 16:15, Christoph Hellwig wrote: > > Agreed. From the description this would seem like a good fit for > q_usage_counter in the block layer, which currently makes creative use > of percpu counters. Yes, if this actually could simplify code that currently used percpu counters, that might be lovely. The percpu counters often perform very well, but then have huge pain in either managing the percpu allocation, or in trying to synchronize across CPU's. I'd be a lot more interested in "we can fix complex code" than in "we have crappy code in bad subsystems where we can hide the performance impact of the subsystem not having been done right". Linus