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[209.85.167.46]) by smtp.gmail.com with ESMTPSA id g11sm1125556ljk.42.2021.11.06.12.10.17 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 06 Nov 2021 12:10:17 -0700 (PDT) Received: by mail-lf1-f46.google.com with SMTP id o18so25957979lfu.13 for ; Sat, 06 Nov 2021 12:10:17 -0700 (PDT) X-Received: by 2002:ac2:57d3:: with SMTP id k19mr13896204lfo.150.1636225817467; Sat, 06 Nov 2021 12:10:17 -0700 (PDT) MIME-Version: 1.0 References: <20211105203851.Ise-VKP1_%akpm@linux-foundation.org> <9f241d37-5db8-4cd2-95c5-ef35844d8b08@www.fastmail.com> In-Reply-To: <9f241d37-5db8-4cd2-95c5-ef35844d8b08@www.fastmail.com> From: Linus Torvalds Date: Sat, 6 Nov 2021 12:10:01 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 080/262] lazy tlb: allow lazy tlb mm refcounting to be configurable To: Andy Lutomirski Cc: Andrew Morton , Anton Blanchard , Benjamin Herrenschmidt , Linux-MM , mm-commits@vger.kernel.org, Nicholas Piggin , Paul Mackerras , Randy Dunlap , "Peter Zijlstra (Intel)" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=RNHsTOUu; spf=pass (imf22.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.208.174 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8C2A4191D X-Stat-Signature: 1eu1wosyiyk3h6e19ww3zxzigy1fhqyb X-HE-Tag: 1636225820-105908 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: Dropped once again until people can agree on this all.. Linus On Fri, Nov 5, 2021 at 9:29 PM Andy Lutomirski wrote: > > So I think there are a few credible choices: > > 1. Find an alternative solution that gets the performance we want without= dangling references. > > 2. Make the MMU_LAZY_TLB_REFCOUNT mode genuinely safe. This means litera= lly ifdeffing out active_mm so it can't dangle. Doing that cleanly will be= a lot of nasty arch work. > > I again apologize that my series is taking so long, although I think it's= finally getting into decent shape. I still need to deal with the scs mess= (that's new), finish tidying up kthread, and make sure hotplug is good. B= ut all this is because this is really hairy code and I'm trying to do it ri= ght. > > If anyone wants to help, help is welcome. Otherwise, I really do intend = to get it all the way done soon. > > --Andy