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[209.85.208.175]) by smtp.gmail.com with ESMTPSA id e2sm4080870lfb.275.2020.09.15.10.35.49 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Sep 2020 10:35:49 -0700 (PDT) Received: by mail-lj1-f175.google.com with SMTP id a22so3524877ljp.13 for ; Tue, 15 Sep 2020 10:35:49 -0700 (PDT) X-Received: by 2002:a19:521a:: with SMTP id m26mr7168489lfb.133.1600191006488; Tue, 15 Sep 2020 10:30:06 -0700 (PDT) MIME-Version: 1.0 References: <20200914204209.256266093@linutronix.de> <871rj4owfn.fsf@nanos.tec.linutronix.de> <20200915062253.GA26275@gondor.apana.org.au> <87een35woz.fsf@nanos.tec.linutronix.de> In-Reply-To: <87een35woz.fsf@nanos.tec.linutronix.de> From: Linus Torvalds Date: Tue, 15 Sep 2020 10:29:50 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 00/13] preempt: Make preempt count unconditional To: Thomas Gleixner Cc: Herbert Xu , Ard Biesheuvel , LKML , linux-arch , Sebastian Andrzej Siewior , Valentin Schneider , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Jeff Dike , Richard Weinberger , Anton Ivanov , linux-um , Brian Cain , linux-hexagon@vger.kernel.org, Geert Uytterhoeven , linux-m68k , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Andrew Morton , Linux-MM , Ingo Molnar , Russell King , Linux ARM , Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , intel-gfx , dri-devel , "Paul E. McKenney" , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Shuah Khan , rcu@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 3E457180B3C83 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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: On Tue, Sep 15, 2020 at 12:24 AM Thomas Gleixner wrote: > > Alternatively we just make highmem a bit more expensive by making these > maps preemptible. RT is doing this for a long time and it's not that > horrible. Ack. In fact, I've wanted to start just removing kmap support entirely. At some point it's not so much about "I have an old machine that wants HIGHMEM" but about "I have an old CPU, and I'll just run an old kernel". It's not that 32-bit is irrelevant, it's that 32-bit with large amounts of memory is irrelevant. Last time this was discussed, iirc the main issue was some questionable old ARM chips that were still very common in embedded environments, even with large memory. But we could definitely start de-emphasizing HIGHMEM. Linus