From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 5BFE46B0007 for ; Tue, 24 Jul 2018 08:24:29 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id z5-v6so1713291edr.19 for ; Tue, 24 Jul 2018 05:24:29 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id k40-v6si4669853ede.416.2018.07.24.05.24.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 Jul 2018 05:24:28 -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: Vlastimil Babka Message-ID: Date: Tue, 24 Jul 2018 14:22:06 +0200 MIME-Version: 1.0 In-Reply-To: <20180724111913.GH28386@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko 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" , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Matthew Wilcox , Miles Chen , Pavel Tatashin , Petr Tesarik 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.