From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-6869-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 210DA985CF2 for ; Mon, 2 Mar 2020 17:40:52 +0000 (UTC) Message-ID: From: Alexander Duyck Date: Mon, 02 Mar 2020 09:40:47 -0800 In-Reply-To: <20200302134941.315212-7-david@redhat.com> References: <20200302134941.315212-1-david@redhat.com> <20200302134941.315212-7-david@redhat.com> MIME-Version: 1.0 Subject: [virtio-dev] Re: [PATCH v1 06/11] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, Michal Hocko , Andrew Morton , "Michael S . Tsirkin" , Juergen Gross , Konrad Rzeszutek Wilk , Pavel Tatashin , Vlastimil Babka , Johannes Weiner , Anthony Yznaga , Michal Hocko , Oscar Salvador , Mel Gorman , Mike Rapoport , Dan Williams , Anshuman Khandual , Qian Cai , Pingfan Liu List-ID: On Mon, 2020-03-02 at 14:49 +0100, David Hildenbrand wrote: > virtio-mem wants to allow to offline memory blocks of which some parts > were unplugged (allocated via alloc_contig_range()), especially, to later > offline and remove completely unplugged memory blocks. The important part > is that PageOffline() has to remain set until the section is offline, so > these pages will never get accessed (e.g., when dumping). The pages shoul= d > not be handed back to the buddy (which would require clearing PageOffline= () > and result in issues if offlining fails and the pages are suddenly in the > buddy). >=20 > Let's allow to do that by allowing to isolate any PageOffline() page > when offlining. This way, we can reach the memory hotplug notifier > MEM_GOING_OFFLINE, where the driver can signal that he is fine with > offlining this page by dropping its reference count. PageOffline() pages > with a reference count of 0 can then be skipped when offlining the > pages (like if they were free, however they are not in the buddy). >=20 > Anybody who uses PageOffline() pages and does not agree to offline them > (e.g., Hyper-V balloon, XEN balloon, VMWare balloon for 2MB pages) will n= ot > decrement the reference count and make offlining fail when trying to > migrate such an unmovable page. So there should be no observable change. > Same applies to balloon compaction users (movable PageOffline() pages), t= he > pages will simply be migrated. >=20 > Note 1: If offlining fails, a driver has to increment the reference > =09count again in MEM_CANCEL_OFFLINE. >=20 > Note 2: A driver that makes use of this has to be aware that re-onlining > =09the memory block has to be handled by hooking into onlining code > =09(online_page_callback_t), resetting the page PageOffline() and > =09not giving them to the buddy. >=20 > Cc: Andrew Morton > Cc: Juergen Gross > Cc: Konrad Rzeszutek Wilk > Cc: Pavel Tatashin > Cc: Alexander Duyck > Cc: Vlastimil Babka > Cc: Johannes Weiner > Cc: Anthony Yznaga > Cc: Michal Hocko > Cc: Oscar Salvador > Cc: Mel Gorman > Cc: Mike Rapoport > Cc: Dan Williams > Cc: Anshuman Khandual > Cc: Qian Cai > Cc: Pingfan Liu > Signed-off-by: David Hildenbrand This addresses the core concerns I had with the patch. Reviewed-by: Alexander Duyck --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org