From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 0C5FC6B0274 for ; Thu, 26 Jul 2018 04:30:45 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id r9-v6so509635edh.14 for ; Thu, 26 Jul 2018 01:30:44 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e18-v6si1014837edb.332.2018.07.26.01.30.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 26 Jul 2018 01:30:43 -0700 (PDT) Date: Thu, 26 Jul 2018 10:30:42 +0200 From: Michal Hocko Subject: Re: [PATCH v1 0/2] mm/kdump: exclude reserved pages in dumps Message-ID: <20180726083042.GC28386@dhcp22.suse.cz> References: <20180720123422.10127-1-david@redhat.com> <9f46f0ed-e34c-73be-60ca-c892fb19ed08@suse.cz> <20180724072237.GA28386@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: Vlastimil Babka , 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 On Thu 26-07-18 10:22:41, David Hildenbrand wrote: > On 24.07.2018 09:22, Michal Hocko wrote: > > On Mon 23-07-18 19:12:58, David Hildenbrand wrote: > >> On 23.07.2018 13:45, 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. > >> > >> I proposed a new flag/value to mask pages that are logically offline but > >> Michal wanted me to go into this direction. > >> > >> While we can special case struct pages in dump tools ("we have to > >> read/interpret them either way, so we can also dump them"), it smells > >> like my original attempt was cleaner. Michal? > > > > But we do not have many page flags spare and even if we have one or two > > this doesn't look like the use for them. So I still think we should try > > the PageReserved way. > > > > So as a summary, the only real approach that would be acceptable is > using PageReserved + some other identifier to mark pages as "logically > offline". > > I wonder what identifier could be used, as this has to be consistent for > all reserved pages (to avoid false positives). > > Using other pageflags in combination might be possible, but then we have > to make assumptions about all users of PageReserved right now. > > As far as I can see (and as has been discussed), page_type could be > used. If we don't want to consume a new bit, we could overload/reuse the > "PG_balloon" bit. > > > E.g. "PG_balloon" set -> exclude page from dump Does each user of PG_balloon check for PG_reserved? If this is the case then yes this would be OK. -- Michal Hocko SUSE Labs