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 B5A16C433F5 for ; Sat, 21 May 2022 19:09:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E5EFE6B0072; Sat, 21 May 2022 15:09:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E0E0E6B0073; Sat, 21 May 2022 15:09:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CD6506B0074; Sat, 21 May 2022 15:09:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id BF15F6B0072 for ; Sat, 21 May 2022 15:09:10 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 86FBF60923 for ; Sat, 21 May 2022 19:09:10 +0000 (UTC) X-FDA: 79490688060.01.50D0A0C Received: from mail-pg1-f170.google.com (mail-pg1-f170.google.com [209.85.215.170]) by imf25.hostedemail.com (Postfix) with ESMTP id DA2B8A0022 for ; Sat, 21 May 2022 19:08:43 +0000 (UTC) Received: by mail-pg1-f170.google.com with SMTP id t28so2776782pga.6 for ; Sat, 21 May 2022 12:09:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=oaRVpI7UKaHjd1HJ1AVlpEJxbT5arsQ6w+vrWxbxyBc=; b=QjeiO2j0PR+bAuyDJSqF15ySQ1DB9sPlRCiEHvyGkkNQOmuBfa8Qcd2TKibjVgehgj GHud8shaYCMMfDYGPXwc/TB2IUe1PuQU21YVJ6nniNXm63Ra9idXakDMhYQ2nWrxpdCQ OB3mD4diRV1Q1fISK9EkJdxpmtHAl42xa+aaF4W0ZTR9Otovkc23b9eZolNW1KbGqBGR nGzZJJEkhPCBKIruDE9S27ibpupAVpxvme3IsQWhG94z+i/Gat1ANKMSLLsMxOoW1RPq LHZzB96fLfe2QvY4AuHtVnWeIFfknkrCwJtTckuLeEF5NklQ6xR83pu6ofh/6PMJ+uOK hpbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=oaRVpI7UKaHjd1HJ1AVlpEJxbT5arsQ6w+vrWxbxyBc=; b=JnyLnvpqylOf9hVdy8Gm7E43O8BsQY22IZRTk3SBqPWJg9d5F7DW0g3/S7trGLIfr7 5B3qzCpb0pGwBfEiaS0Qi0Z3mpk3RzmMXuAYjbnar3T1atRhOwh0tRgwA68kDymjAld4 F/2eTBK5FXM9kXYDNh57lQyrqatvsnlAkVm02lbCQ3Pd1v+A4Z1n2PUOs82Hc8vrgsJn CmMLsPBe8HZ7rpuaP7Bz6P7xIReCu+CpBmTpWjZYdOgY+tzgPu3qDkkv+8l8o1JIxS3e HCUiUbqy6OdRP2YnYxdJc/kkdyQzOykxLePvK0E5LYcNuo2UewZWCJLiOn5+VR4ROep7 nznQ== X-Gm-Message-State: AOAM5338gTqmna7ErR3UspBAW1NGWc5EX2BTTZfuPuSa9lfwa0P9Rtz2 ZzkRm272MoCfaLAk0+cympU= X-Google-Smtp-Source: ABdhPJzp0ax3vDQvWbw9hzTH2DploUMC323OlGwE4au2JvTYsmhwhQ+S2X3uHGw7ahxTgjXRU9KoCg== X-Received: by 2002:a05:6a00:178c:b0:518:86a0:3deb with SMTP id s12-20020a056a00178c00b0051886a03debmr3127347pfg.64.1653160148593; Sat, 21 May 2022 12:09:08 -0700 (PDT) Received: from strix-laptop (2001-b011-20e0-15d4-84b3-8c62-a0b8-199e.dynamic-ip6.hinet.net. [2001:b011:20e0:15d4:84b3:8c62:a0b8:199e]) by smtp.gmail.com with ESMTPSA id w5-20020a1709027b8500b001619fbb0e6dsm1959649pll.40.2022.05.21.12.09.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 21 May 2022 12:09:08 -0700 (PDT) Date: Sun, 22 May 2022 03:08:59 +0800 From: Chih-En Lin To: Qi Zheng Cc: David Hildenbrand , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Christian Brauner , "Matthew Wilcox (Oracle)" , 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 , Andy Lutomirski , Sebastian Andrzej Siewior , Fenghua Yu , linux-kernel@vger.kernel.org, Kaiyang Zhao , Huichun Feng , Jim Huang , Andrew Morton , linux-mm@kvack.org Subject: Re: [External] [RFC PATCH 0/6] Introduce Copy-On-Write to Page Table Message-ID: <20220521190859.GA1551274@strix-laptop> References: <20220519183127.3909598-1-shiyn.lin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=QjeiO2j0; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf25.hostedemail.com: domain of shiyn.lin@gmail.com designates 209.85.215.170 as permitted sender) smtp.mailfrom=shiyn.lin@gmail.com X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: DA2B8A0022 X-Stat-Signature: ysi95a6cw7cb5p4sqcnou4jxfdmkiabb X-HE-Tag: 1653160123-766517 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 04:59:19PM +0800, Qi Zheng wrote: > Hi, > > To reduce the empty user PTE tables, I also introduced a reference > count (pte_ref) for user PTE tables in my patch[1][2], It is used > to track the usage of each user PTE tables. > > The following people will hold a pte_ref: > - The !pte_none() entry, such as regular page table entry that map > physical pages, or swap entry, or migrate entry, etc. > - Visitor to the PTE page table entries, such as page table walker. > > With COW PTE, a new holder (the process using the COW PTE) is added. > > It's funny, it leads me to see more meaning of pte_ref. > > Thanks, > Qi > > [1] [RFC PATCH 00/18] Try to free user PTE page table pages > link: https://lore.kernel.org/lkml/20220429133552.33768-1-zhengqi.arch@bytedance.com/ > (percpu_ref version) > > [2] [PATCH v3 00/15] Free user PTE page table pages > link: https://lore.kernel.org/lkml/20211110105428.32458-1-zhengqi.arch@bytedance.com/ > (atomic count version) > > -- > Thanks, > Qi Hi, I saw your patch a few months ago. Actually, my school's independent study is tracing the page table. And one of the topics is your patch. It is really helpful from your pte_ref. It's great to see you have more ideas for your pte_ref. Thanks.