From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88FABC64E7A for ; Tue, 1 Dec 2020 18:42:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C5B9021741 for ; Tue, 1 Dec 2020 18:42:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EYoLlsZk" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5B9021741 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:43896 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kkAbH-0001kN-Pe for qemu-devel@archiver.kernel.org; Tue, 01 Dec 2020 13:42:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:58486) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kkAaM-00016O-T2 for qemu-devel@nongnu.org; Tue, 01 Dec 2020 13:41:10 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:33828) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kkAaK-0005zW-I0 for qemu-devel@nongnu.org; Tue, 01 Dec 2020 13:41:10 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606848067; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=EDLMKMOMeQcOO8kAElzyOyqRcVJFfn9e5B+cCQQXzUU=; b=EYoLlsZkEjNtpZrmK4w+eX2rrjphAT7yoyRHUR2oVFMo1KI+hbHTlZuTFu0vlqqA2Mv+9/ hDvWREKvOqhVouQ4opBflGL7JVoGPTbOV8nLKAyRDFCYW5Hw4XWBIWwVDbxxa7KvSasARi O1ZCsCIeaZi3RA20w2KpCpixcoojPP0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-56-FvrNusRaNnacShaL511ipw-1; Tue, 01 Dec 2020 13:41:05 -0500 X-MC-Unique: FvrNusRaNnacShaL511ipw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 328AC1005E58; Tue, 1 Dec 2020 18:41:04 +0000 (UTC) Received: from work-vm (ovpn-115-1.ams2.redhat.com [10.36.115.1]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 731DD5D6AD; Tue, 1 Dec 2020 18:40:58 +0000 (UTC) Date: Tue, 1 Dec 2020 18:40:55 +0000 From: "Dr. David Alan Gilbert" To: Andrey Gruzdev Subject: Re: [PATCH v4 0/6] UFFD write-tracking migration/snapshots Message-ID: <20201201184055.GM4338@work-vm> References: <20201126151734.743849-1-andrey.gruzdev@virtuozzo.com> <20201201070820.GO105758@angien.pipo.sk> <20201201105300.GQ105758@angien.pipo.sk> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.497, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Krempa , Juan Quintela , qemu-devel@nongnu.org, Peter Xu , Markus Armbruster , Paolo Bonzini , Den Lunev Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Andrey Gruzdev (andrey.gruzdev@virtuozzo.com) wrote: > On 01.12.2020 13:53, Peter Krempa wrote: > > On Tue, Dec 01, 2020 at 11:42:18 +0300, Andrey Gruzdev wrote: > > > On 01.12.2020 10:08, Peter Krempa wrote: > > > > On Thu, Nov 26, 2020 at 18:17:28 +0300, Andrey Gruzdev via wrote: > > > > > This patch series is a kind of 'rethinking' of Denis Plotnikov's ideas he's > > > > [...] > > > > > > Note that in cases when qemu can't guarantee that the > > > > background_snapshot feature will work it should not advertise it. We > > > > need a way to check whether it's possible to use it, so we can replace > > > > the existing --live flag with it rather than adding a new one and > > > > shifting the problem of checking whether the feature works to the user. > > > > > > > > > > Hi, > > > > > > May be you are using hugetlbfs as memory backend? > > > > Not exactly hugepages, but I had: > > > > > > > > > > > > which resulted into the following commandline to instantiate memory: > > > > -object memory-backend-file,id=pc.ram,mem-path=/var/lib/libvirt/qemu/ram/6-upstream-bj/pc.ram,share=yes,size=33554432000,host-nodes=0,policy=bind \ > > > > When I've removed it I got: > > > > -object memory-backend-ram,id=pc.ram,size=33554432000,host-nodes=0,policy=bind \ > > > > And the migration didn't fail in my quick test. I'll have a more > > detailed look later, thanks for the pointer. > > > > Yep, seems that current userfaultfd supports hugetlbfs and shared memory for > missing pages but not for wr-protected.. For hugepages, you'd need kernel support - but also you'd want to make sure you write the whole hugepage at once. For shared, there's a harder problem to ask; what happens if RAM is written by the other process - for postcopy, we get the other process to send us a userfaultfd that they have registered with their VM. Dave > > > I totally agree that we need somehow check that kernel and VM memory backend > > > support the feature before one can enable the capability. > > > Need to think about that.. > > > > Definitely. Also note that memory backed by memory-backend-file will be > > more and more common, for cases such as virtiofs DAX sharing and > > similar. > > > > I see.. That needs support from kernel side, so far 'background-snapshots' > are incompatible with memory-backend-file sharing. > > -- > Andrey Gruzdev, Principal Engineer > Virtuozzo GmbH +7-903-247-6397 > virtuzzo.com > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK