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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 B4677C6778A for ; Tue, 24 Jul 2018 11:19:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 755DA20856 for ; Tue, 24 Jul 2018 11:19:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 755DA20856 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388400AbeGXMZP (ORCPT ); Tue, 24 Jul 2018 08:25:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:48744 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2388196AbeGXMZP (ORCPT ); Tue, 24 Jul 2018 08:25:15 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 86942ACBB; Tue, 24 Jul 2018 11:19:15 +0000 (UTC) Date: Tue, 24 Jul 2018 13:19:13 +0200 From: Michal Hocko To: Vlastimil Babka Cc: David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Baoquan He , Dave Young , Greg Kroah-Hartman , Hari Bathini , Huang Ying , "Kirill A. Shutemov" , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Matthew Wilcox , Miles Chen , Pavel Tatashin , Petr Tesarik Subject: Re: [PATCH v1 0/2] mm/kdump: exclude reserved pages in dumps Message-ID: <20180724111913.GH28386@dhcp22.suse.cz> References: <20180720123422.10127-1-david@redhat.com> <9f46f0ed-e34c-73be-60ca-c892fb19ed08@suse.cz> <20180723123043.GD31229@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 24-07-18 11:47:02, Vlastimil Babka wrote: > On 07/23/2018 02:30 PM, Michal Hocko wrote: > > On Mon 23-07-18 13:45:18, Vlastimil Babka wrote: > >> On 07/20/2018 02:34 PM, David Hildenbrand wrote: > >>> Dumping tools (like makedumpfile) right now don't exclude reserved pages. > >>> So reserved pages might be access by dump tools although nobody except > >>> the owner should touch them. > >> > >> Are you sure about that? Or maybe I understand wrong. Maybe it changed > >> recently, but IIRC pages that are backing memmap (struct pages) are also > >> PG_reserved. And you definitely do want those in the dump. > > > > You are right. reserve_bootmem_region will make all early bootmem > > allocations (including those backing memmaps) PageReserved. I have asked > > several times but I haven't seen a satisfactory answer yet. Why do we > > even care for kdump about those. If they are reserved the nobody should > > really look at those specific struct pages and manipulate them. Kdump > > tools are using a kernel interface to read the content. If the specific > > content is backed by a non-existing memory then they should simply not > > return anything. > > When creating a crashdump, I definitely need the pages containing memmap > included in the dump, so I can inspect the struct pages. But this is a > bit recursive issue, so I'll try making it clearer: > > 1) there are kernel pages with data (e.g. slab) that I typically need in > the dump, and are not PageReserved > 2) there are struct pages for pages 1) in the memmap that physically > hold the pageflags for 1), and these are PageReserved > 3) there are struct pages for pages 2) somewhere else in the memmap, > physically hold the pageflags for 2). They are probably also > PageReserved themselves ? and self-referencing. > > Excluding PageReserved from dump means there won't be cases 2) and 3) in > the dump, which at least for case 2) is making such dump almost useless > in many cases. Yes, we cannot simply exclude all PageReserved pages. I was merely suggesting to rule out new special PageReserved pages that are denoting offline pages. The same could be applied to HWPoison pages -- Michal Hocko SUSE Labs