From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965658AbeEXI4g (ORCPT ); Thu, 24 May 2018 04:56:36 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:60536 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965188AbeEXI4a (ORCPT ); Thu, 24 May 2018 04:56:30 -0400 Date: Thu, 24 May 2018 16:56:11 +0800 From: Dave Young To: David Hildenbrand Cc: Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Potapenko , Andrew Morton , Andrey Ryabinin , Balbir Singh , Baoquan He , Benjamin Herrenschmidt , Boris Ostrovsky , Dan Williams , Dmitry Vyukov , Greg Kroah-Hartman , Hari Bathini , Huang Ying , Hugh Dickins , Ingo Molnar , Jaewon Kim , Jan Kara , =?iso-8859-1?B?Suly9G1l?= Glisse , Joonsoo Kim , Juergen Gross , Kate Stewart , "Kirill A. Shutemov" , Matthew Wilcox , Mel Gorman , Michael Ellerman , Miles Chen , Oscar Salvador , Paul Mackerras , Pavel Tatashin , Philippe Ombredanne , Rashmica Gupta , Reza Arbab , Souptick Joarder , Tetsuo Handa , Thomas Gleixner , Vlastimil Babka Subject: Re: [PATCH v1 00/10] mm: online/offline 4MB chunks controlled by device driver Message-ID: <20180524085610.GA5467@dhcp-128-65.nay.redhat.com> References: <20180523151151.6730-1-david@redhat.com> <20180524075327.GU20441@dhcp22.suse.cz> <14d79dad-ad47-f090-2ec0-c5daf87ac529@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <14d79dad-ad47-f090-2ec0-c5daf87ac529@redhat.com> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, [snip] > > > >> For kdump and onlining/offlining code, we > >> have to mark pages as offline before a new segment is visible to the system > >> (e.g. as these pages might not be backed by real memory in the hypervisor). > > > > Please expand on the kdump part. That is really confusing because > > hotplug should simply not depend on kdump at all. Moreover why don't you > > simply mark those pages reserved and pull them out from the page > > allocator? > > 1. "hotplug should simply not depend on kdump at all" > > In theory yes. In the current state we already have to trigger kdump to > reload whenever we add/remove a memory block. > > > 2. kdump part > > Whenever we offline a page and tell the hypervisor about it ("unplug"), > we should not assume that we can read that page again. Now, if dumping > tools assume they can read all memory that is offline, we are in trouble. > > It is the same thing as we already have with Pg_hwpoison. Just a > different meaning - "don't touch this page, it is offline" compared to > "don't touch this page, hw is broken". Does that means in case an offline no kdump reload as mentioned in 1)? If we have the offline event and reload kdump, I assume the memory state is refreshed so kdump will not read the memory offlined, am I missing something? > > Balloon drivers solve this problem by always allowing to read unplugged > memory. In virtio-mem, this cannot and should even not be guaranteed. > Hmm, that sounds a bug.. > And what we have to do to make this work is actually pretty simple: Just > like Pg_hwpoison, track per page if it is online and provide this > information to kdump. > > Thanks Dave