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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 BD795C4CC71 for ; Wed, 23 Sep 2020 10:23:10 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DB8BC2388A for ; Wed, 23 Sep 2020 10:23:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pNi62cLp" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB8BC2388A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BxDlY5C3MzDqYk for ; Wed, 23 Sep 2020 20:23:05 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1236::1; helo=casper.infradead.org; envelope-from=peterz@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=infradead.org Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BxDjG1D62zDqLn for ; Wed, 23 Sep 2020 20:21:06 +1000 (AEST) 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 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> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , David Airlie , Sebastian Andrzej Siewior , Joonas Lahtinen , dri-devel , linux-mips@vger.kernel.org, Ben Segall , Max Filippov , Guo Ren , linux-sparc , Vincent Chen , Will Deacon , Ard Biesheuvel , linux-arch , Vincent Guittot , Herbert Xu , the arch/x86 maintainers , Russell King , linux-csky@vger.kernel.org, Mel Gorman , "open list:SYNOPSYS ARC ARCHITECTURE" , linux-xtensa@linux-xtensa.org, Paul McKenney , intel-gfx , linuxppc-dev , Steven Rostedt , Jani Nikula , Rodrigo Vivi , Dietmar Eggemann , Linux ARM , Chris Zankel , Michal Simek , Thomas Bogendoerfer , Nick Hu , Linux-MM , Linus Torvalds , LKML , Arnd Bergmann , Daniel Vetter , Vineet Gupta , Paul Mackerras , Andrew Morton , Daniel Bristot de Oliveira , "David S. Miller" , Greentime Hu Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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.