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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 612B0C433F5 for ; Sun, 22 May 2022 00:31:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7488C8D0006; Sat, 21 May 2022 20:31:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6F8AF8D0003; Sat, 21 May 2022 20:31:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C02E8D0006; Sat, 21 May 2022 20:31:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 4D1DE8D0003 for ; Sat, 21 May 2022 20:31:24 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 181F5209BD for ; Sun, 22 May 2022 00:31:24 +0000 (UTC) X-FDA: 79491500088.16.1D22E21 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf07.hostedemail.com (Postfix) with ESMTP id DD04340024 for ; Sun, 22 May 2022 00:31:13 +0000 (UTC) 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=b11yj7k2aWIJUC0HrAN1JE6uNRPyX/9gm1nWkGjLk8o=; b=lYHaz3uAV41tpTBPj8WDZh8ZPQ sFOmAQT7jhCNSrbgQhokByzyVkd++Ic4ak1j53Ov4P8TaQVc7wXPASxAdNJi2i3nGioAD6P5hssEp CZTjfna3vBly3tZNaIUELdmOvmK6ThyN75wky9w3yxyRRLMqfugtOr+U98BRM09tYmlMSaRIp2H+c gkxvYiN04zeBX1+i6WOeTOMIN+XJO0YigONeojJcb5spgWMT3o+n1kH+r51hERAeeaCV5JKyBtVS9 3TlEOnaSU4v5zXTPkNTFZZEZJc2DileQIVzkYDEgioEdIzWTgS0xPiTnkmHvXZcSATjbfOq1cMZiW 9orNnJtg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nsZUs-00F1WZ-C7; Sun, 22 May 2022 00:31:02 +0000 Date: Sun, 22 May 2022 01:31:02 +0100 From: Matthew Wilcox To: Andy Lutomirski Cc: David Hildenbrand , Chih-En Lin , Andrew Morton , linux-mm@kvack.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Christian Brauner , Vlastimil Babka , William Kucharski , John Hubbard , Yunsheng Lin , Arnd Bergmann , Suren Baghdasaryan , Colin Cross , Feng Tang , "Eric W. Biederman" , Mike Rapoport , Geert Uytterhoeven , Anshuman Khandual , "Aneesh Kumar K.V" , Daniel Axtens , Jonathan Marek , Christophe Leroy , Pasha Tatashin , Peter Xu , Andrea Arcangeli , Thomas Gleixner , Sebastian Andrzej Siewior , Fenghua Yu , linux-kernel@vger.kernel.org, Kaiyang Zhao , Huichun Feng , Jim Huang Subject: Re: [RFC PATCH 0/6] Introduce Copy-On-Write to Page Table Message-ID: References: <20220519183127.3909598-1-shiyn.lin@gmail.com> <64d0da08-6ffd-4bce-bc66-5097913937b4@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <64d0da08-6ffd-4bce-bc66-5097913937b4@kernel.org> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: DD04340024 X-Rspam-User: Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=lYHaz3uA; spf=none (imf07.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Stat-Signature: z7k51suby6m85trtq7azzxehencj7ep8 X-HE-Tag: 1653179473-636130 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 Sat, May 21, 2022 at 03:19:24PM -0700, Andy Lutomirski wrote: > I can see a rather different use for this type of shared-pagetable > technology, though: monstrous MAP_SHARED mappings. For database and some VM > users, multiple processes will map the same file. If there was a way to > ensure appropriate alignment (or at least encourage it) and a way to handle > mappings that don't cover the whole file, then having multiple mappings > share the same page tables could be a decent efficiently gain. This doesn't > even need COW -- it's "just" pagetable sharing. The mshare proposal did not get a warm reception at LSFMM ;-( The conceptual model doesn't seem to work for the MM developers who were in the room. "Fear" was the most-used word. Not sure how we're going to get to a model of sharing page tables that doesn't scare people.