From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f200.google.com (mail-qk0-f200.google.com [209.85.220.200]) by kanga.kvack.org (Postfix) with ESMTP id 8126B6B000C for ; Tue, 24 Jul 2018 08:33:23 -0400 (EDT) Received: by mail-qk0-f200.google.com with SMTP id b185-v6so3341121qkg.19 for ; Tue, 24 Jul 2018 05:33:23 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id v36-v6si1236894qvc.168.2018.07.24.05.33.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 Jul 2018 05:33:22 -0700 (PDT) Subject: Re: [PATCH v1 0/2] mm/kdump: exclude reserved pages in dumps References: <20180720123422.10127-1-david@redhat.com> <9f46f0ed-e34c-73be-60ca-c892fb19ed08@suse.cz> <20180723123043.GD31229@dhcp22.suse.cz> <20180724111913.GH28386@dhcp22.suse.cz> From: David Hildenbrand Message-ID: Date: Tue, 24 Jul 2018 14:33:13 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka , Michal Hocko Cc: 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" , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Matthew Wilcox , Miles Chen , Pavel Tatashin , Petr Tesarik On 24.07.2018 14:22, Vlastimil Babka wrote: > On 07/24/2018 01:19 PM, Michal Hocko wrote: >>> 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 > > So how about marking them with some "page type" that we got after > Matthew's struct page reorg? I assume the pages we're talking about are > in a state that they don't need the mapcount/mapping field or whatever > unions with the page type... but I guess some care would be needed to > not have false positives when the union field is actually used but > happens to look like the new type. > Had that implemented, Michal didn't like it so far. ("waste of one bit") -- Thanks, David / dhildenb