From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755291AbaJULUo (ORCPT ); Tue, 21 Oct 2014 07:20:44 -0400 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:34269 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755039AbaJULUm (ORCPT ); Tue, 21 Oct 2014 07:20:42 -0400 Date: Tue, 21 Oct 2014 13:20:25 +0200 From: Dominik Dingel To: Paolo Bonzini Cc: Martin Schwidefsky , Dave Hansen , Andrew Morton , linux-mm@kvack.org, Mel Gorman , Michal Hocko , Rik van Riel , Andrea Arcangeli , Andy Lutomirski , "Aneesh Kumar K.V" , Bob Liu , Christian Borntraeger , Cornelia Huck , Gleb Natapov , Heiko Carstens , "H. Peter Anvin" , Hugh Dickins , Ingo Molnar , Jianyu Zhan , Johannes Weiner , "Kirill A. Shutemov" , Konstantin Weitz , kvm@vger.kernel.org, linux390@de.ibm.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Peter Zijlstra , Sasha Levin Subject: Re: [PATCH 2/4] mm: introduce new VM_NOZEROPAGE flag Message-ID: <20141021132025.60dd3390@BR9TG4T3.de.ibm.com> In-Reply-To: <5446153F.6030407@redhat.com> References: <1413554990-48512-1-git-send-email-dingel@linux.vnet.ibm.com> <1413554990-48512-3-git-send-email-dingel@linux.vnet.ibm.com> <54419265.9000000@intel.com> <20141018164928.2341415f@BR9TG4T3.de.ibm.com> <54429521.80402@intel.com> <5445511D.1090603@redhat.com> <20141021081131.641c6104@mschwide> <5446153F.6030407@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102111-0041-0000-0000-000001C0F3C2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 21 Oct 2014 10:11:43 +0200 Paolo Bonzini wrote: > > > On 10/21/2014 08:11 AM, Martin Schwidefsky wrote: > >> I agree with Dave (I thought I disagreed, but I changed my mind while > >> writing down my thoughts). Just define mm_forbids_zeropage in > >> arch/s390/include/asm, and make it return mm->context.use_skey---with a > >> comment explaining how this is only for processes that use KVM, and then > >> only for guests that use storage keys. > > > > The mm_forbids_zeropage() sure will work for now, but I think a vma flag > > is the better solution. This is analog to VM_MERGEABLE or VM_NOHUGEPAGE, > > the best solution would be to only mark those vmas that are mapped to > > the guest. That we have not found a way to do that yet in a sensible way > > does not change the fact that "no-zero-page" is a per-vma property, no? > > I agree it should be per-VMA. However, right now the code is > complicated unnecessarily by making it a per-VMA flag. Also, setting > the flag per VMA should probably be done in > kvm_arch_prepare_memory_region together with some kind of storage key > notifier. This is not very much like Dominik's patch. All in all, > mm_forbids_zeropage() provides a non-intrusive and non-controversial way > to fix the bug. Later on, switching to vma_forbids_zeropage() will be > trivial as far as mm/ code is concerned. > Thank you for all the feedback, will cook up a new version.