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=-5.8 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 9A433C6379F for ; Mon, 23 Nov 2020 13:14:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5ACFF2076E for ; Mon, 23 Nov 2020 13:14:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="BovGW7Do" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388589AbgKWNNt (ORCPT ); Mon, 23 Nov 2020 08:13:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:41246 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388568AbgKWNNo (ORCPT ); Mon, 23 Nov 2020 08:13:44 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1606137221; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rv9w9/llZazFt1Z6bqz4fjM+bsJ8PYyhjd+2a7iwKww=; b=BovGW7DoOC8krOpDGxMAvISB+An1UZdqsVUv0y+mOwCm8gQma8GRfSmZfwYSeLpHtd4a0/ tL9UdmdQTm1PU6J92WQP00NeFdV6eO8Y3Y0lZDPaeByUGaMvOUAdiycCP9E47AAgaodsRu q3uicdbuKCt6m7LZUTwpc+6v7wB2XDg= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 78EB1AC2E; Mon, 23 Nov 2020 13:13:41 +0000 (UTC) Date: Mon, 23 Nov 2020 14:13:39 +0100 From: Michal Hocko To: Matthew Wilcox 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: <20201123131339.GO27488@dhcp22.suse.cz> References: <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> <20201123124513.GI4327@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201123124513.GI4327@casper.infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 23-11-20 12:45:13, Matthew Wilcox wrote: > 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(). You are right. I have managed to completely confuse myself. Sorry about the noise! -- Michal Hocko SUSE Labs