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 9BB62C2D0E4 for ; Mon, 23 Nov 2020 12:45:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0A37A20732 for ; Mon, 23 Nov 2020 12:45:51 +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="eeEoYa3p" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A37A20732 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 48C056B005D; Mon, 23 Nov 2020 07:45:51 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4622E6B0072; Mon, 23 Nov 2020 07:45:51 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 329DD6B0073; Mon, 23 Nov 2020 07:45:51 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0176.hostedemail.com [216.40.44.176]) by kanga.kvack.org (Postfix) with ESMTP id 055406B005D for ; Mon, 23 Nov 2020 07:45:50 -0500 (EST) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id A6F1F9893 for ; Mon, 23 Nov 2020 12:45:50 +0000 (UTC) X-FDA: 77515654860.06.fork03_3a0305327365 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin06.hostedemail.com (Postfix) with ESMTP id 866981003759F for ; Mon, 23 Nov 2020 12:45:50 +0000 (UTC) X-HE-Tag: fork03_3a0305327365 X-Filterd-Recvd-Size: 3978 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Mon, 23 Nov 2020 12:45:49 +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=D/+uQXuYCHVJTryMNhtIQ0wirxLovQ10MM/7dftfXjA=; b=eeEoYa3psy1tQ0tTz+3MV500iq llvX2Sq8XRxLgLc4WkoFbfknD5IuMj5jxeQbAoExJ8GueJ5c7jbEdBYzy4ZAv5TgoNvzjoYcaAJE2 NY3ZUBdJMTt+QbgdfbWC0Blm/oZq+tJsp7r6NZhWe6bK11IlKbXjWJCKokcbLb6f0r0ZWuw98vK33 /NgveDC9KrZI+yM1PMYnsRCLpwGDyj5/6DHqZ7Skbu8j1mhFfbLHoFlwy5JPoK7PbBKu1/LoDzr5h M35LHR3GTV8EJpVz41HDlLhuiX/y/RVJPHyPje9sA5X1J9Nwv4d+N89FUyEUsROJ6Ktf+W7q8/u/m 6jp0E+bQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1khBDV-0000hM-8q; Mon, 23 Nov 2020 12:45:13 +0000 Date: Mon, 23 Nov 2020 12:45:13 +0000 From: Matthew Wilcox To: Michal Hocko Cc: Muchun Song , Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Oscar Salvador , "Song Bao Hua (Barry Song)" , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Subject: Re: [External] Re: [PATCH v5 00/21] Free some vmemmap pages of hugetlb page Message-ID: <20201123124513.GI4327@casper.infradead.org> References: <20201120064325.34492-1-songmuchun@bytedance.com> <20201120084202.GJ3200@dhcp22.suse.cz> <20201120131129.GO3200@dhcp22.suse.cz> <20201123074046.GB27488@dhcp22.suse.cz> <20201123094344.GG27488@dhcp22.suse.cz> <20201123104258.GJ27488@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201123104258.GJ27488@dhcp22.suse.cz> 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 Mon, Nov 23, 2020 at 11:42:58AM +0100, Michal Hocko wrote: > On Mon 23-11-20 18:36:33, Muchun Song wrote: > > > No I really mean that pfn_to_page will give you a struct page pointer > > > from pages which you release from the vmemmap page tables. Those pages > > > might get reused as soon sa they are freed to the page allocator. > > > > We will remap vmemmap pages 2-7 (virtual addresses) to page > > frame 1. And then we free page frame 2-7 to the buddy allocator. > > And this doesn't really happen in an atomic fashion from the pfn walker > POV, right? So it is very well possible that > > struct page *page = pfn_to_page(); > // remapping happens here > // page content is no longer valid because its backing memory can be > // reused for whatever purpose. pfn_to_page() returns you a virtual address. That virtual address remains a valid pointer to exactly the same contents, it's just that the page tables change to point to a different struct page which has the same compound_head().