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[209.85.218.44]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a993f939550sm80656466b.42.2024.10.05.09.56.42 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Oct 2024 09:56:42 -0700 (PDT) Received: by mail-ej1-f44.google.com with SMTP id a640c23a62f3a-a8d24f98215so476533566b.1 for ; Sat, 05 Oct 2024 09:56:42 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCV7cM3i+IMyImXWnX95LKoDHYAacY9aEgRD+QcrRQYMhexynfu96VhtF9nmDAXvv1QcxaPj1Qbcpg==@kvack.org X-Received: by 2002:a17:907:3e05:b0:a93:d5d3:be4 with SMTP id a640c23a62f3a-a991bd16c3fmr599542466b.13.1728147401876; Sat, 05 Oct 2024 09:56:41 -0700 (PDT) MIME-Version: 1.0 References: <20241002010205.1341915-1-mathieu.desnoyers@efficios.com> <20241005161537.GB18071@noisy.programming.kicks-ass.net> In-Reply-To: <20241005161537.GB18071@noisy.programming.kicks-ass.net> From: Linus Torvalds Date: Sat, 5 Oct 2024 09:56:24 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 0/4] sched+mm: Track lazy active mm existence with hazard pointers To: Peter Zijlstra Cc: Mathieu Desnoyers , Andrew Morton , linux-kernel@vger.kernel.org, Nicholas Piggin , Michael Ellerman , Greg Kroah-Hartman , Sebastian Andrzej Siewior , "Paul E. McKenney" , Will Deacon , Boqun Feng , Alan Stern , John Stultz , Neeraj Upadhyay , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Lai Jiangshan , Zqiang , Ingo Molnar , Waiman Long , Mark Rutland , Thomas Gleixner , Vlastimil Babka , maged.michael@gmail.com, Mateusz Guzik , Jonas Oberhauser , rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 5466D8000E X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: o6g54efisaumd69cby7swkryx9tm6k14 X-HE-Tag: 1728147406-577481 X-HE-Meta: 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 mMFNkuW3 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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 Sat, 5 Oct 2024 at 09:16, Peter Zijlstra wrote: > > On Wed, Oct 02, 2024 at 10:39:15AM -0700, Linus Torvalds wrote: > > So I think the real issue is that "active_mm" is an old hack from a > > bygone era when we didn't have the (much more involved) full TLB > > tracking. > > I still seem to have these patches that neither Andy nor I ever managed > to find time to finish: > > https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=x86/lazy Yes, that looks very much like what I had in mind. In fact, it looks a lot smaller and simpler than what my mental model was. I was thinking I'd do it by removing "active_mm" entirely from 'struct task_struct', and turn it into a per-cpu variable instead, and then try to massage that into some global new world order. That patch series you point to seems to be much simpler and clearer. Of course, you also say "never managed to finish", so presumably there's something completely broken in that series, and it doesn't actually work? Linus