From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 30541C2D0A8 for ; Wed, 23 Sep 2020 10:21:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD3C720C56 for ; Wed, 23 Sep 2020 10:21:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pNi62cLp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726497AbgIWKVO (ORCPT ); Wed, 23 Sep 2020 06:21:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726130AbgIWKVO (ORCPT ); Wed, 23 Sep 2020 06:21:14 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06077C0613CE; Wed, 23 Sep 2020 03:21:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=O4A3QRP4HEH7pkY19EFh0K5o5RX6GGVTm9jhhlkiNIA=; b=pNi62cLpz5Zta9gkWwEt4lfxLS MvhJOB6wShDmzS61MUaHO4PpqjGN9Sm/CRsoDDzFeOKdB1AsXqzPU0+ObaxataHs7GirJ6ZZrNA29 JPWLW2cWAsjQWQbdxWBW0dcBjYBOhFdcukcR730OctenEgtMdnxXFf2H16Xmyh8kGL1vudzudnTWS vgNOihiXykvGZ4JuqnJtzxEEw21LcbXj/0WRtpi2vf37zyqZKGgA0xHxtS+lCluMZDHojS7jgks+j aId3Dnzk0AyXRqRRmekuY3B5xhsSuZTtpZucjls9NPVPsQXWrpdBaC7TpOBBrZeOKsQtIyaebVCjb X6rPNsiw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL1sU-00033a-DF; Wed, 23 Sep 2020 10:19:58 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 0EA94301124; Wed, 23 Sep 2020 12:19:54 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E35462B79EDA9; Wed, 23 Sep 2020 12:19:53 +0200 (CEST) Date: Wed, 23 Sep 2020 12:19:53 +0200 From: peterz@infradead.org To: Thomas Gleixner Cc: Linus Torvalds , LKML , linux-arch , Paul McKenney , the arch/x86 maintainers , Sebastian Andrzej Siewior , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Andrew Morton , Linux-MM , 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 , Ard Biesheuvel , Herbert Xu , Vineet Gupta , "open list\:SYNOPSYS ARC ARCHITECTURE" , Arnd Bergmann , Guo Ren , linux-csky@vger.kernel.org, Michal Simek , Thomas Bogendoerfer , linux-mips@vger.kernel.org, Nick Hu , Greentime Hu , Vincent Chen , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev , "David S. Miller" , linux-sparc Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Message-ID: <20200923101953.GT2674@hirez.programming.kicks-ass.net> References: <20200919091751.011116649@linutronix.de> <87mu1lc5mp.fsf@nanos.tec.linutronix.de> <87k0wode9a.fsf@nanos.tec.linutronix.de> <87eemwcpnq.fsf@nanos.tec.linutronix.de> <87a6xjd1dw.fsf@nanos.tec.linutronix.de> <87sgbbaq0y.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sgbbaq0y.fsf@nanos.tec.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Mon, Sep 21, 2020 at 09:27:57PM +0200, Thomas Gleixner wrote: > Alternatively this could of course be solved with per CPU page tables > which will come around some day anyway I fear. Previously (with PTI) we looked at making the entire kernel map per-CPU, and that takes a 2K copy on switch_mm() (or more general, the user part of whatever the top level directory is for architectures that have a shared kernel/user page-table setup in the first place). The idea was having a fixed per-cpu kernel page-table, share a bunch of (kernel) page-tables between all CPUs and then copy in the user part on switch. I've forgotten what the plan was for ASID/PCID in that scheme. For x86_64 we've been fearing the performance of that 2k copy, but I don't think we've ever actually bit the bullet and implemented it to see how bad it really is.