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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7E6D8C7618B for ; Mon, 29 Jul 2019 15:00:08 +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 461052067D for ; Mon, 29 Jul 2019 15:00:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 461052067D 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]:52864 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hs78B-0004wx-4c for qemu-devel@archiver.kernel.org; Mon, 29 Jul 2019 11:00:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37369) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hs76q-0003JZ-1F for qemu-devel@nongnu.org; Mon, 29 Jul 2019 10:58:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hs76p-0004HK-0b for qemu-devel@nongnu.org; Mon, 29 Jul 2019 10:58:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56964) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hs76o-0004GA-RU; Mon, 29 Jul 2019 10:58:42 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B280E30A7C63; Mon, 29 Jul 2019 14:58:40 +0000 (UTC) Received: from gondolin (dhcp-192-232.str.redhat.com [10.33.192.232]) by smtp.corp.redhat.com (Postfix) with ESMTP id A23325C21A; Mon, 29 Jul 2019 14:58:29 +0000 (UTC) Date: Mon, 29 Jul 2019 16:58:27 +0200 From: Cornelia Huck To: Igor Mammedov Message-ID: <20190729165827.565d6265.cohuck@redhat.com> In-Reply-To: <20190729145229.4333-1-imammedo@redhat.com> References: <20190729145229.4333-1-imammedo@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Mon, 29 Jul 2019 14:58:40 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH RFC 0/2] s390: stop abusing memory_region_allocate_system_memory() 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: Thomas Huth , David Hildenbrand , qemu-devel@nongnu.org, dgilbert@redhat.com, Christian Borntraeger , qemu-s390x@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 29 Jul 2019 10:52:27 -0400 Igor Mammedov wrote: cc:ing some folks for awareness. > While looking into unifying guest RAM allocation to use hostmem backends > for initial RAM (especially when -mempath is used) and retiring > memory_region_allocate_system_memory() API, leaving only single hostmem backend, > I was inspecting how currently it is used by boards and it turns out several > boards abuse it by calling the function several times (despite documented contract > forbiding it). > > s390 is one of such boards where KVM limitation on memslot size got propagated > to board design and memory_region_allocate_system_memory() was abused to satisfy > KVM requirement for max RAM chunk where memory region alias would suffice. > > Unfortunately, memory_region_allocate_system_memory() usage created migration > dependency where guest RAM is transferred in migration stream as several RAMBlocks > if it's more than KVM_SLOT_MAX_BYTES. > > In order to replace these several RAM chunks with a single memdev and keep it > working with KVM memslot size limit and migration compatible, following was done: > * [2/2] use memory region aliases to partition hostmem backend RAM on > KVM_SLOT_MAX_BYTES chunks, which should keep KVM side working > * [1/2] hacked memory region aliases (to ram memory regions only) to have > its own RAMBlocks pointing to RAM chunks owned by aliased memory > region. While it's admittedly a hack, but it's relatively simple and > allows board code rashape migration stream as necessary > > I haven't tried to use migratable aliases on x86 machines, but with it > it could be possible to drop legacy RAM allocation and compat knob > (cd5ff8333a) dropping '-numa node,mem' completely even for old machines. > > PS: > Tested with ping pong cross version migration on s390 machine > (with reduced KVM_SLOT_MAX_BYTES since I don't have access to large > enough host) > > > Igor Mammedov (2): > memory: make MemoryRegion alias migratable > s390: do not call memory_region_allocate_system_memory() multiple > times > > exec.c | 7 ++++--- > hw/s390x/s390-virtio-ccw.c | 20 +++++++++++++++----- > memory.c | 5 +++++ > 3 files changed, 24 insertions(+), 8 deletions(-) >